TCVN 7777-1 : 2008

TIU CHUN QUC GIA

TCVN 7777-1 : 2008

ISO/IEC GUIDE 43-1 : 1997TH NGHIM THNH THO BNG SO SNH LIN PHNG TH NGHIM - LN 1: XY DNG V TRlN KHAI CC CHNG TRNH TH NGHIM THNH THO

Proficiency testing by interlaboratory comparisons- Part 1: Development and operation of proficiency testing schemesLi ni u

TCVN 7777-1 : 2008 hon ton tng ng vi ISO/IEC Guide 43-1 : 1997.

TCVN 7777-1 : 2008 do Ban k thut tiu chun TCVN/TC 176 Qun l cht lng v m bo cht lng bin son, Tng cc Tiu chun o lng Cht lng ngh, B Khoa hc v Cng ngh cng b.

TCVN 7777-1 : 2008 l mt phn ca b tiu chun TCVN 7777 (ISO/IEC Guide 43). B tiu chun ny gm 2 phn c tn chung Th nghim thnh tho bng so snh lin phng th nghim:

- Phn 1: Xy dng v trin khai cc chng trnh th nghim thnh tho.

- Phn 2: La chn v s ng cc chng trnh th nghim thnh tho ca t chc cng nhn phng th nghim.Li gii thiu

So snh lin phng th nghim (sau y gi l so snh lin phng) c thc hin vi nhiu mc ch v c th c s tham gia ca cc phng th nghim v cc bn khc

V d, so snh lin phng c s dng :

a) xc nh vic thc hin ca cc phng th nghim ring l i vi cc php o hoc th nghim c th v theo di hot ng lin tc ca cc phng th nghim

b) nhn bit cc vn trong cc phng th nghim v c ngay nhng hnh ng khc phc v d nh lin quan n nhn vin thc hin hay hiu chun thit b;

c) thit lp tnh hiu lc v kh nng so snh ca cc phng php th hay phng php o mi v tng t nh vy theo di cc phng php c thit lp;

d) cung cp thm bng chng cho khch hng ca phng th nghim;

e) nhn bit s khc nhau gia cc phng th nghim;

f) xc nh cc c im tnh nng ca phng php - thng l th nghim phi hp;

g) n nh gi tr cho mu chun v nh gi s ph hp s dng trong cc quy trnh o lng v th nghim c th.

Th nghim thnh tho c dng trong so snh lin phng vi mc ch a), ngha l xc nh vic thc hin hot ng o lng v th nghim ca phng th nghim. Tuy nhin vic trin khai cc chng trnh th nghim thnh tho cng thng cung cp thng tin cho cc mc ch khc nu trn.

Vic tham gia vo cc chng trnh th nghim thnh tho cung cp cho cc phng th nghim tin cy v cc d liu m h a ra vi phng php nh gi v th hin khch quan. Mc d c mt s loi chng trnh th nghim thnh tho (xem iu 4), nhng phn ln u c c trng chung v so snh kt qu th nghim, o lng thu c t hai hay nhiu phng th nghim.

Mt trong s cc u im chnh ca cc chng trnh th nghim thnh tho l nh gi nng lc thc hin php th mt cch thnh tho ca cc phng th nghim. Vic ny c th bao gm vic t nh gi ca phng th nghim, nh gi ca khch hng hoc ca cc bn khc nh cc t chc cng nhn, hoc c quan c thm quyn. V vy n s b sung cho cc th tc kim sot cht lng ni b ca cc phng th nghim thng qua vic cung cp bin php b sung bn ngoi v kh nng th nghim ca h. Hot ng ny cng nng cao k thut nh gi ti ch phng th nghim ca cc chuyn gia k thut (thng c s dng bi cc t chc cng nhn phng th nghim). S tin cy vo kt qu m phng th nghim hay hiu chun t c mt cch nht qun l iu c tm quan trng ln i vi khch hng s dng dch v th nghim. Nhng khch hng tm kim s m bo nh vy c th t nh gi cc kt qu th nghim hoc s dng vic nh gi ca cc t chc khc.

Trong khi tiu chun ny nhn mnh vo vic trin khai hot ng so snh lin phng i vi th nghim thnh tho, th phn ln cc nguyn tc v hng dn c a ra c th p dng cho vic trin khai cc so snh lin phng vi nhng mc ch khc.

Trong khi c nhiu t chc cng nhn phng th nghim trin khai cc chng trnh th nghim thnh tho ca ring h, th cng c mt s lng ng k s dng cc chng trnh th nghim thnh tho hoc cc phng thc so snh lin phng khc do t chc khc thc hin. Mc ch ca TCVN 7777-2 : 2008 l a ra cc nguyn tc hi ha cho vic la chn phng thc so snh lin phng ph hp dng lm chng trnh th nghim thnh tho ca cc t chc cng nhn phng th nghim.

Phn ln cc t chc nh gi nng lc k thut ca phng th nghim yu cu hoc mong i vic thc hin tho ng cc chng trnh th nghim thnh tho nh l bng chng quan trng v kh nng a ra cc kt qu tin cy ca phng th nghim (tr trng hp th nghim thnh tho l khng thch hp).

Tuy nhin cn nhn mnh rng c mt s khc bit ln gia:

a) nh gi nng lc phng th nghim thng qua vic nh gi ton b hot ng da trn cc yu cu c xc nh, v

b) vic kim tra kt qu tham gia th nghim thnh tho ca phng th nghim ch c th c xem l cung cp thng tin v nng lc k thut ca phng th nghim mt thi im nht nh trong cc iu kin c th ca php th (hay cc php th) trong mt chng trnh th nghim thnh tho c th.

Tiu chun ny c tham kho mt s ti liu hng dn lin quan n th nghim thnh tho ca cc t chc: ILAC; ISO (TC69); ISO/REMCO; IUPAC; AOAC; ASTM v WECC, WELAC (nay st nhp thnh EAL).TH NGHIM THNH THO BNG SO SNH LIN PHNG TH NGHIM - LN 1: XY DNG V TRlN KHAI CC CHNG TRNH TH NGHIM THNH THO

Proficiency testing by interlaboratory comparisons- Part 1: Development and operation of proficiency testing schemes1. Phm vi p dng

Trong khi c nhiu u im ca vic so snh lin phng cng vi s a dng trong thit k v thc thi, th vn c th quy nh nhng nguyn tc thit yu cn c xem xt khi t chc vic so snh ny. Tiu chun ny xc nh cc nguyn tc v m t cc yu t tnh n trong t chc v thc hin cc chng trnh th nghim thnh tho.

TCVN 7777-2 : 2008 m t cch thc m t chc cng nhn phng th nghim nh gi nng lc k thut ca cc phng th nghim, cn la chn v s dng cc chng trnh th nghim thnh tho.

Tiu chun ny nhm mc ch s dng cho ngi trin khai v ngi s dng chng trnh th nghim thnh tho nh cc phng th nghim tham gia, t chc cng nhn, c quan c thm quyn v khch hng ca cc dch v th nghim c nhu cu nh gi nng lc k thut ca phng th nghim. Tiu chun ny cng c bit hu ch trong vic t nh gi ca cc phng th nghim, nhng cng phi tha nhn rng th nghim thnh tho ch l mt phng php c th gp phn vo vic thit lp s tin cy ln nhau gia nhng ngi s dng cc phng th nghim khc nhau.

Hin ti y cng l iu kin ca mt s t chc cng nhn yu cu cc phng th nghim tham gia thng xuyn vo cc chng trnh th nghim thnh tho m t chc cng nhn chp nhn l ph hp v mc ch. V vy, iu thit yu l nhng ngi trin khai cc chng trnh th nghim ny phi tun th cc nguyn tc qun l mt cch chuyn nghip cc chng trnh th nghim thnh tho trong c yu cu k thut, th tc thng k (xem v d trong Ph lc A) v trong qun l cht lng (xem hng dn trong Ph lc B).

Phng php trin khai trong phm vi cc t chc th nghim thnh tho khc nhau khng nht thit phi hon ton tng ng v tiu chun ny khng a ra hng dn chi tit cho hot ng trin khai c th trong so snh lin phng. Ni dung ca tiu chun ch nhm thit lp khun kh chung trn c s c th sa i cho ph hp vi tng hon cnh c th, bao gm c nhng chng trnh c s lng ngi tham gia nhiu hay t.

Tiu chun ny khng cp n k thut m cc t chc thng dng nh gi vic thc hin ca phng th nghim n l thng qua vic giao np mu chun c chng nhn hoc cc mu th nghim tiu biu khc.

Th mc ti liu tham kho c nu trong Ph lc C.

2. Ti liu vin dn

Cc ti liu vin dn di y rt cn thit cho vic p dng tiu chun ny. i vi cc ti liu ghi nm cng b th p dng bn c nu. i vi cc ti liu khng ghi nm cng b th p dng bn mi nht, bao gm c cc sa i.

ISO 3534-1:1993, Statistics - Vocabulary and symbols - Part 1: Probability and general statistical terms (Thng k - T vng v k hiu - Phn 1: Xc sut v thut ng chung v thng k)

TCVN 6910-1 : 2001 (ISO 5725-1 : 1994), chnh xc ( ng v chm) ca phng php o v kt qu o - Phn 1: Nguyn tc v nh ngha chung

TCVN 6910-2 : 2001 (ISO 5725-2 : 1994), chnh xc ( ng v chm) ca phng php o v kt qu o - Phn 2: Phng php c bn xc nh lp li v ti lp ca phng php o tiu chunTCVN 6910-4 : 2001 (ISO 5725-4 : 1994), chnh xc ( ng v chm) ca phng php o V kt qu o - Phn 4: Cc phng php c bn xc nh ng ca phng php o tiu chun

B tiu chun TCVN ISO 9000 v H thng qun l cht lng

TCVN 6450 : 2007 (ISO/IEC Guide 2 : 2004), Tiu chun ho v cc hot ng lin quan - Thut ng chung

TCVN ISO/IEC 17025 : 2007 (ISO/IEC 17025 : 2005), Yu cu chung v nng lc ca phng th nghim v hiu chun

TCVN 7777-2 : 2008 (ISO/IEC Guide 43-2 : 1997), Th nghim thnh tho bng so snh lin phng th nghim - Phn 2: La chn v ng dng chng trnh th nghim thnh tho ca t chc cng nhn phng th nghim

Guide to Expression of Uncertainty in Measurement: 1993, issued by BIPM; IEC; IFCC; ISO; IUPA; IUPAP; OIML (Hng dn th hin khng m bo o do BIPM; IEC; IFCC; ISO; IUPAC; IUP/ OIML ban hnh)

International vocabulary of basic and general terms in metrology : 1993, issued by BIPM; IEC; IFCC; ISO; IUPAP; OIML (T vng quc t v thut ng chung v c bn trong o lng do BIPM- IEC; IFCC; ISO; IUPAP; OIML ban hnh) [VIM 1993]

The international Harmonized Protocol for the Proficiency Testing of (Chemical) Analytical Laboratories (Tho thun hi ho quc t v th nghim thnh tho ca Phng th nghim phn tch (ho hc)).

Evaluation of Matrix Effects: Proposed Guideline, NCCLS Document EP - 14P, National Committee for Clinical Laboratory Standards, Villanova, PA, 1994 (nh gi nhng nh hng ma trn: Hng dn xut ca Ban k thut quc gia v cc tiu chun ca Phng th nghim y t)

3. Thut ng v nh ngha

Tiu chun ny p dng cc nh ngha di y. Mt s nh ngha c trch t cc Hng dn ca ISO v Tiu chun quc t khc.

3.1

Php th (test)

Hot ng k thut bao gm vic xc nh mt hoc nhiu c tnh ca mt sn phm, qu trnh hay dch v theo mt th tc quy nh.

[TCVN 6450 : 2007 (ISO/IEC Guide 2)]

3.2

Phng th nghim (testing laboratory)

Phng th nghim thc hin cc th nghim

CH THCH: Thut ng phng th nghim c th c dng theo ngha mt thc th php l, k thut hoc c hai trng hp

[TCVN 6450 : 2007 (ISO/IEC Guide 2)]

3.3

Mu th nghim (test item)

Vt liu hoc mu phng tin o giao np cho phng th nghim tham gia hot ng th nghim thnh tho.

3.4

Phng php th (test method)

Quy trnh k thut xc nh thc hin th nghim.

[TCVN 6450 : 2007 (ISO/IEC Guide 2)]3.5

Kt qu th (test result)

Gi tr ca c tnh thu c sau khi thc hin hon chnh mt phng php o xc nh.

[TCVN 6910-1 : 2001 (ISO 5725-1 : 1994)]

3.6

Th nghim thnh tho (phng th nghim) ((laboratory) proficiency testing)

Vic xc nh hot ng th nghim ca phng th nghim bng so snh lin phng.

[TCVN 6450 : 2007 (ISO/IEC Guide 2)]

CH THCH: Vi mc ch ca tiu chun ny, thut ng th nghim thnh tho phng thi nghim c dng vi ngha rng nht v bao gm, v d nh:

a) Chng trnh nh tnh - v d trng hp cc phng th nghim c yu cu xc nh mt thnh phn cua mu th nghim.

b) Thc hin bin i d liu - v d trng hp cc phng th nghim c cung cp tp d liu v c yu cu vn dng d liu cung cp thm thng tin.

c) Th nghim mu n - trng hp mt mu c gi ti mt s phng th nghim mt cch lin tc v tr ngi t chc sau mt khong thi gian.

d) Thc hin mt ln - trng hp phng th nghim c cung cp mu th nghim cho mt thi im n l.

e) Chng trnh lin tc - trng hp phng th nghim c cung cp u n cc mu th nghim trn c lin tc.

f) Ly mu - v d khi c nhn hay t chc c yu cu ly mu cho phn tch tip theo.

3.7So snh lin phng (interlaboratory comparisons)

Vic t chc, thc hin v nh gi cc th nghim trn cng mt mu th nghim hoc mu th nghim tng t c thc hin bi hai hay nhiu phng th nghim theo cc iu kin xc nh trc

CH THCH: Trong mt s trng hp, mt trong cc phng th nghim tham gia vo so snh lin phng c th phng th nghim cung cp gi tr n nh cho mu th nghim.

3.8

Mu chun (RM) (reference material)

Vt liu hoc cht c mt hay nhiu gi tr v tnh cht ca n c xc nh ng nht v tt hiu chun mt thit b, nh gi mt phng php o hoc n nh cc gi tr ca vt liu.

[TCVN 6165:1996 (VIM:1993), 6.13]

3.9

Mu chun c chng nhn (CRM) (Certified reference material)

Mu chun c km theo giy chng nhn, trong mt hay nhiu gi tr v tnh cht ca n c chng nhn theo mt th tc nhm thit lp s lin kt vi vic th hin chnh xc n v m theo cc gi tr v tnh cht c biu th ra v mi gi tr c chng nhn c km theo khng m bao tng ng mc tin cy quy nh.

[TCVN 6165:1996 (VIM:1993), 6.14]

3.10

Phng th nghim quy chiu (reference laboratory)

Phng th nghim cung cp gi tr quy chiu cho mt mu th nghim.

CH THCH: V d nh Phng hiu chun quc gia.

3.11

Gi tr n nh (assigned value)

Gi tr quy cho mt i lng ring bit v c chp nhn, i khi bng tha c, c khng m bao ph hp vi mc ch nh.

[TCVN 6165:1996 (VIM:1993), 1.20 v ch thch 1 v 2)

3.12

Tinh lin kt chun (traceability)

Tinh cht ca kt qu o hoc gi tr ca mt chun m nh c th lin h ti nhng chun nh, thng l chun quc gia hay quc t, thng qua mt chui so snh khng gin on vi nhng khng m bo nh.

[TCVN 6165:1996 (VIM:1993), 6.10]

3.13

iu phi vin (coordinator)

T chc (hay c nhn) c trch nhim iu phi tt c cc hot ng lin quan trong vic trin khai mt chng trnh th nghim thnh tho.

3.14

ng (trueness)

Mc gn nhau gia gi tr trung binh ca mt dy ln cc kt qu th nghim v gi tr quy chiu c chp nhn.

[ISO 3534-1]3.15

chm (precision)

Mc gn nhau gia cc kt qu th nghim c lp nhn c trong iu kin quy nh.

[ISO 3534-1]

3.16

Gi tr bt thng (outlier)

Phn t ca mt tp hp cc gi tr khng ph hp vi cc phn t khc ca tp hp [TCVN 6910-1 : 2001 (ISO 5725-1 : 1994)]

3.17

Kt qua ngoi bin (extreme results)

Gia tr bt thng v cc gia tr khc hon ton khng ph hp vi cc phn t khc ca tp hp tai liu.

CH THCH: Nhng kt qua ny c th c nh hng ln n thng k tng hp nh lch trung binh v lch chun.

3.18

K thut thng k th (robust statistical techniques)

K thut hn ch nh hng ca cc kt qu ngoi bin gy ra cho vic c lng lch trung bnh v lch chun.

CH THCH: Nhng k thut ny ch gim bt nh hng ca cc kt qu ngoi bin ch khng loi c chng khi tp hp d liu.

3.19

khng m bo o (uncertainty of measurement)

Thng s gn vi kt qu ca php o, c trng cho s phn tn ca cc gi tr c th quy cho s lng o mt cch hp l.

[TCVN 6165:1996 (VIM:1993), 3.9]

4. Cc loi th nghim thnh tho

4.1. Khi qut

Cc k thut th nghim thnh tho khc nhau tu thuc vo tnh cht ca mu th nghim, phng php s dng v s lng phng th nghim tham gia. Phn ln c c trng chung l so snh kt qua thu c ca mt phng th nghim vi cc kt qu thu c t mt hoc nhiu phng th nghim khac. Trong mt s chng trnh, mt trong cc phng th nghim tham gia c th c chc nng kim soat iu phi hoc quy chiu.

Di y l cc loi chng trnh th nghim thnh tho ph bin.

4.2 .Chng trnh so snh o lng

Chng trnh so snh o lng i hi mu th cn o hay hiu chun phi c lun chuyn lin tip t phng th nghim tham gia ny n phng th nghim k tip. Thng thng c trng ca cc chng trnh ny l:

a) Gia tr n nh cho mu th nghim do phng th nghim quy chiu cung cp, y c th l c quan quyn lc cao nht ca quc gia i vi php o lin quan. Mu th nghim c th cn c kim tra nhng giai on nht nh trong sut qu trnh tin hnh th nghim thnh tho. iu ny nhm m bo khng co thay i ng k no v gi tr n nh trong sut qu trnh th nghim thnh tho.

b) hon thnh cc chng trnh ny i hi s tham gia lin tc (trong mt s trng hp cn n hng nm). iu ny gy nn mt s kh khn nh: am bao n nh ca mu th nghim; theo di cht ch vic lun chuyn v thi gian cho php i vi php o ca ring cc bn tham gia; v s cn thit phi cung cp thng tin phn hi v vic thc hin n l cho cc phng th nghim trong sut qua trnh trin khai chng trnh th nghim ch khng phi ch n khi kt thc. Ngoi ra, vic so snh kt qu theo nhm s c th kh khn v c th c tng i t phng th nghim c nng lc o tng xng nhau.

c) Cc kt qu o ring l c so snh vi gi tr quy chiu do phng th nghim quy chiu thit lp. iu phi vin phi tnh n khng m bo o ca tng phng th nghim tham gia.

d) Cc v d v mu th nghim (mu phng tin o) c dng trong loi th nghim thnh tho ny bao gm c cc chun chnh (v d in tr, dng v phng tin o)

4.3. Chng trnh th nghim lin phng

Chng trnh th nghim lin phng vi cc mu th c chn ngu nhin t ngun vt liu c phn phi ng thi cho cc phng th nghim tham gia cng th nghim. i khi k thut ny cng c s dng cho chng trnh o lin phng. Sau khi hon thnh th nghim, kt qu c gi tr li c quan iu phi v c so snh vi (cc) gi tr n nh a ra chi s vic thc hin ca phng th nghim n l v ca ton b nhm.

Cc v d v mu th nghim c dng trong loi th nghim thnh tho ny bao gm thc phm, cht lu ca c th, nc, t v vt liu mi trng khc. Trong mt vi trng hp, cc phn ring l ca mu chun c thit lp (chng nhn) trc khi c lun chuyn.

iu thit yu l mi l mu th nghim cung cp cho cc bn tham gia trong mi chu k phi ng nht bt k kt qu no sau o c xc nh l ngoi bin khng c quy cho bt k s bin i ng k no ca mu th nghim, (xem 5.6.2 v A.4 trong Ph lc A)Chng trnh th nghim lin phng thng c t chc cng nhn, c quan c thm quyn v cac chc khc s dng, khi h p dng cc chng trnh trong lnh vc th nghim.

Mt loi chng trnh th nghim lin phng ph bin l thit k "phn cp trong cc mc ca lng o tng t nhau (nhng khng ng nht) thuc hai mu th nghim ring bit. Thit k ny c s dng c lng chm ca phng th nghim mt mc xc nh ca i lng o. iu ny nhm trnh cc vn lin quan n php o lp li trn cng mu th nghim hoc kt hp mu th nghim ging nhau trong cng mt chu k th nghim thnh tho.

4.4. Chng trnh th nghim vi mu tch

Mt dng th nghim thnh tho c bit thng c khch hng ca cc phng th nghim, bao gm c cc c quan c thm quyn s dng l k thut th vi mu tch. (Khng nn nhm ln k thut vi chng trnh phn cp nu trong 4.3).

Thng thng th nghim vi mu tch dng trong so snh d liu c a ra bi nhm nh cho (phng th nghim (thng ch hai phng th nghim) ang c nh gi l nh cung ng dch v th nghim tim nng hay lin tc.

So sanh lin phng tng t thng c thc hin trong giao dch thng mi khi cc mu th nghim i din mt hng thng mi c phn chia gia phng th nghim i din cho ngi cung ng phng th nghim khc i din cho ngi mua. Mu th nghim b sung thng c gi li cho phng th nghim ca bn th ba kim tra khi cn s phn x trong trng hp c s khc nhau ng k gia kt qu do phng th nghim pha ngi cung ng v phng th nghim pha ngi a ra.

Chng trnh th nghim vi mu tch i hi cc mu ca mt sn phm hay vt liu c tch thanh hai hay nhiu phn vi tng phng th nghim tham gia th nghim mt phn ca tng mu. Cc chng trnh ny khc vi dng th nghim thnh tho m t 4.3, v thng co rt t phng thi nghim tham gia (thng l hai). Cc ng dng ca loi chng trnh ny bao gm vic nhn bit ..thp, vic m ta dc ng nht v xc nhn tnh hiu lc ca hnh ng khc phc.

Cc chng trnh ny thng cn lu vt liu gii quyt mi khc bit nhn bit c gia ... cc phng thi nghim tham gia bng cc phn tch su hn ca cc phng th nghim b sung.

Mt k thut th vi mu tch tng t cng c s dng trong vic gim st phng th nghim y t mi trng. Thng thng, cc chng trnh ny bao gm kt qu t mt s mu tch ph kho nng rng c so snh gia mt phng th nghim ring l vi mt hay nhiu phng thi nghim khc. Vi nhng chng trnh ny, mt trong s cc phng th nghim c th c coi l hot ng trnh o lng cao hn (ngha l khng m bo mc thp hn) nh ng dng phng phap quy chiu v thit b hin i hn,... Kt qu ca cc phng th nghim ny c th c coi l gi tr quy chiu trong cc so snh lin phng ny v c th ng vai tr phng th nghim t vn hay hng dn i vi cc phng th nghim khc trong vic so snh d liu ca th nghim tch mu vi n.4.5. Chng trnh nh tnh

nh gi vic thc hin th nghim ca phng th nghim khng nht thit phi tham gia vo so snh lin phng [(xem im a) trong ch thch ca 3.6], V d mt s chng trnh c thit k nh gi kh nng ca phng thi nghim nhm m t cc thc th c th (v d nh dng aming nhn dng sinh vt gy bnh c trng,...).

Chng trnh ny c th cn s chun b c bit cc mu th nghim vi s b sung thnh phn ph thuc ca iu phi vin chng trnh. Nh vy, cc chng trnh ny v bn cht l "nh tnh'' v khng cn s tham gia ca nhiu phng th nghim hay so snh lin phng nh gi vic thc hin th nghim ca phng th nghim.

4.6. Chng trnh cho trc gi tr

Mt dng chng trnh th nghim thnh tho c bit khc c th i hi phi chun b cc mu th nghim vi s lng bit ca i lng o c th. Sau c th nh gi kh nng ca phng th nghim ring l trong vic th nghim cc mu v cung cp kt qu bng s so snh vi gi tr n nh. Loi chng trnh ny cng khng cn s tham gia ca nhiu phng th nghim.

4.7. Chng trnh thc hin tng phn qu trnh

Cc dng c bit ca th nghim thnh tho i hi vic nh gi nng lc ca phng th nghim thc hin cc phn ca qu trnh th nghim hoc o lng tng th. V d, mt vi chng trnh hin c nh gi nng lc ca phng th nghim trong vic bin i v bo co mt tp hp d liu cho trc (thay v tin hnh php th hoc php o thc) hoc ly mu v chun b mu hay b mu theo quy nh k thut.

5. T chc v thit k

5.1. Phm vi

5.1.1. Giai on thit k ca bt k chng trnh th nghim thnh tho no u i hi s tham gia ca chuyn gia k thut, thng k vin v iu phi vin chng trnh nhm m bo s thnh cng v vic trin khai mt cch sun s.

5.1.2. iu phi vin, thng qua vic trao i vi nhng ngi khc, cn xy dng chng trnh ph hp vi th nghim thnh tho c th. Mt chng trinh th nghim thnh tho cn c thit k nhm trnh bt k s nhm ln no v mc ch ca n. K hoch cn c thng nht v lp thnh vn bn (xem Ph lc B) trc khi bt u chng trnh v thng bao gm cc thng tin sau:

a) tn v a ch ca t chc tin hnh chng trnh thnh tho;

b) tn v a ch ca iu phi vin v nhng ngi khc tham gia vo vic thit k v trin khai chng trnh thnh tho;

c) bn cht v mc ch ca chng trnh thnh tho;

d) th tc v cch thc la chn ngi tham gia, khi thch hp, hoc cc tiu ch cn p ng trc c php tham gia;

e) tn v a ch ca phng th nghim hay cc phng th nghim thc hin (nhng phn ca) chng trnh (v d ly mu, x l mu, th nghim tnh ng nht v n nh gi tr) v s lng ngi tham gia d kin;

f) bn cht ca (cc) mu th nghim v (cc) php th c la chn cng nh bn m t tm tt vic xem xt u tin cc la chn;

g) bn m t v cch thc nhn, x l, kim tra v vn chuyn mu th nghim;

h) bn m t cc thng tin cung cp cho ngi tham gia vo giai on thng bo ny v k hoch thi gian cho cc giai on khc nhau ca th nghim thnh tho;

i) k hn hay thi hn bt u v kt thc d kin ca chng trnh thnh tho bao gm c thi hn cho ngi tham gia thc hin th nghim;

j) tn sut phn phi mu th nghim vi nhng chng trnh lin tip;

k) thng tin v phng php hay th tc m ngi tham gia c th cn s dng thc hin cc phng th hay php o (thng l th tc thng thng);

l) bn s lc v phn tch thng k cn s dng, bao gm vic xc nh cc gi tr n nh v bt k k thut pht hin gi tr bt thng no;

m) bn m t thng tin hoc d liu c gi tr li cho ngi tham gia; n) c s ca k thut nh gi vic thc hin;

o) bn m t phm vi cng khai kt qu php th v kt lun da trn kt qu th nghim thnh tho5.2. Nhn vin

Nhn vin tham gia vo vic cung cp chng trnh cn c, hoc cng tc cht ch vi ngi nng lc v kinh nghim trong thit k, trin khai v lp bo co v cc so snh lin phng cng cn c c cc k nng v k thut, thng k v qun tr thch hp.5.2.2. Nh nu trong 5.1.1, vic trin khai so snh lin phng c th cng i hi ch dn ca ngi am hiu chi tit v k thut v c kinh nghim v phng php v th tc th nghim lin quan. Vi mc ch ny, iu phi vin c th cn tuyn chn mt hay nhiu c nhn thch hp lm vic nh nhm t vn, v d c ly ra t c quan chuyn ngnh, phng th nghim thu (nu c), nhng ngi tham gia chng trnh hay ngi s dng d liu.

5.2.3. Chc nng ca nhm t vn ny c th bao gm:

a) xy dng v sot xt cc th tc cho vic hoch nh, thc hin, phn tch, bo co v tinh hiu lc ca chng trnh th nghim thnh tho;

b) nhn bit v nh gi so snh lin phng c t chc bi cc c quan khc;

c) nh gi kt qu th nghim thnh tho lin quan vic thc hin ca cc phng th nghim tham gia;

d) cung cp ch dn cho bt k c quan nh gi nng lc k thut ca phng th nghim tham gia no v kt qu t c trong sut chng trnh th nghim thnh tho cng nh cch s dng kt qu ny vi cc kha cnh khc ca nh gi phng th nghim;

e) cung cp ch dn cho ngi tham gia v cc vn kinh nghim r rng; v

f) gii quyt bt k bt ng no gia iu phi vin v ngi tham gia.

5.3. Thit b x l d liu

Bt k thit b no c s dng u cn phi ph hp tin hnh nhp tt c d liu cn thit cng nh phn tch thng k v a ra cc kt qu kp thi, c gi tr. Cc th tc kim tra d liu u vo cn phi c tin hnh, cc phn mm cn phi c kim tra xc nhn, h tr v sao lu. Cn phi kim sot vic lu tr v bo mt cc tp tin d liu.

5.4. Thit k thng k

5.4.1. M hnh thng k v cc k thut phn tch d liu s dng cn phi c lp thnh vn bn cng vi mt bn m t tm tt v c s la chn. Chi tit hn v cc th tc thng k ph bin v vic x l d liu th nghim thnh tho c nu trong Ph lc A.

5.4.2. Thit k thng k ph hp ca chng trnh th nghim thnh tho l thit yu. Cn xem xt k lng cc vn sau v s tng tc ca chng:

a) chm v ng ca cc php th lin quan;b) khc bit nh nht gia cc phng th nghim tham gia cn c pht hin mc tin cy yu cu;

c) s lng phng th nghim tham gia;

d) s lng mu cn th v s ln lp li php th hoc php o cn thc hin trn mi mu th nghim;e) quy trnh dng c lng gi tr n nh;

f) th tc s dng xc nh gi tr bt thng.

5.4.3. Khi thiu thng tin tin cy lin quan n im a), th trong mt s trng hp cn t chc snh lin phng th im (th nghim cng tc) t c yu cu ny.

5.5. Chun b mu th nghim

5.5.1. Vic chun b mu th nghim cng c th c iu phi vin cho thu hoc m nhn. V t chc chun b mu th nghim cn th hin nng lc lm vic ny.

5.5.2. Bt k iu kin no lin quan n mu th nghim c th nh hng n tnh ton vn ca so snh lin phng, nh tnh ng nht, vic ly mu, n nh, kh nng h hi dc ng v nhng nh hng ca iu kin xung quanh u cn c xem xt (xem 5.6).

5.5.3. Mu th nghim hoc vt liu th nghim c phn phi trong chng trnh ni chung ging nhau v bn cht vi cc loi thng thng c th nghim bi cc phng th nghim tham giaCH THCH: V d v tho thun cho vic thit lp s tng ng c nu trong ti liu NCCLS EP-14P do ban quc gia v tiu chun phng th nghim y t Villanova, PA, xut bn nm 1994.

5.5.4. S mu th nghim c phn phi c th ph thuc vo vic c hay khng c yu cu tng qut tp hp cc thnh phn cu to.

5.5.5. (Cc) gi tr n nh khng cn phi cng b cho nhng ngi tham gia cho ti sau khi kt qu c i chiu. Tuy nhin, trong mt vi trng hp c th chi dn cc phm vi mc tiu trc khi th nghim.

5.5.6. Vic chun b mu th nghim b sung khc ngoi cc mu cn thit cho chng trnh th nghim thnh tho cn c a ra xem xt. Cc mu th nghim d c th hu ch lm mu chun, mu kim sot cht lng hay h tr o to cho cc phng th nghim sau khi kt qu nhng ngi tham gia c nh gi.

5.6. Qun l mu th nghim

5.6.1. Th tc ly mu, ly mu ngu nhin, vn chuyn, tip nhn, nhn dng, ghi nhn lu kho v x l hng mc th nghim cn c lp thnh vn bn.

5.6.2. Trong trng hp vt liu khi lng ln c chun b cho th nghim thnh tho chng cn ng nht hon ton i vi tng tham s th nghim tt c cc phng th nghim nhn c mu th nghim khng c khc bit ng k v tham s c o. iu phi vin cn lp thnh vn bn th tc s dng thit lp tnh ng nht ca mu th nghim (xem A.4 trong Ph lc A). Khi c th cn tin hnh th nghim tnh ng nht trc khi gi mu th nghim cho cc phng th nghim tham gia. Mc ng nht cn t n mc m s khc bit gia cc mu th nghim khng gy nh hng ng k n vic nh gi kt qu ca ngi tham gia.

5.6.3. Khi c th, iu phi vin cng cn cung cp bng chng chng t mu th nghim l n nh m bo chng c th chu c bt k thay i ng k no trong sut qu trnh tin hnh th nghim thnh tho. Khi cc i lng o khng n nh cn c nh gi, t chc iu phi c th cn quy nh thi gian hon thnh th nghim v cc th tc cn thit c bit trc th nghim.

5.6.4. iu phi vin cn xem xt n bt k mi nguy no m mu th nghim c th gy ra v a ra chi dn thch hp cho cc bn c th b ri ro bi cc mi nguy tim n (v d ngi phn phi vt liu th nghim, phng th nghim,...).

5.7. La chn phng php/th tc

5.7.1. Thng thng cc bn tham gia c th s dng phng php h la chn ph hp vi th tc thng thng c dng trong cc phng th nghim. Tuy nhin, trong cc trng hp nht nh, iu phi vin c th hng dn ngi tham gia s dng mt phng php quy nh. Phng php ny thng l phng php tiu chun c tha nhn cp quc gia hoc quc t v c xc nhn gi tr s dng bng mt th tc thch hp (v d th nghim cng tc).

5.7.2. Khi s dng th tc hiu chun, gi tr n nh thng l gi tr quy chiu t c t php o do phng hiu chun cp cao thc hin (thng l Phng th nghim chun quc gia) s dng cc th tc c xc nh r v c chp nhn. Cc phng th nghim tham gia cn s dng cng th tc hoc s dng cc th tc tng t nhau nhng vi cc phng hiu chun th khng phi khi no cng t c iu ny.

5.7.3. Trong trng hp cc bn tham gia c t do s dng phng php h la chn, iu phi vin cn yu cu thng tin chi tit v phng php cho php so snh cc kt qu ca cc bn tham gia v gp v phng php khi thch hp.

5.8. S tin trin ca cc chng trnh th nghim thnh tho

Nhm m bo chng trnh th nghim thnh tho thch hp vi s pht trin ca khoa hc v k thut cn c cc loi mu mi, phng php hay th tc mi. Cc kt lun ban u t kt qu thc hin ca cc phng th nghim ring l ca nhng chng trnh ny cn c a ra mt cch thn trng. (Xem 6.4.3)

6. Trin khai v lp bo co

6.1. Vic iu phi v vn bn ha

Vic trin khai chng trnh thng ngy cn do mt iu phi vin chu trch nhim. Tt c cc hot ng v th tc cn c lp thnh vn bn. Cc ti liu ny c th bao gm, hoc c b sung trong s tay cht lng. (Xem Ph lc B)

6.2. Hng dn

6.2.1. Cn phi cung cp cc hng dn chi tit cho ton b cc kha cnh ca chng trnh m cc phng th nghim tham gia chp thun. V d cc hng dn ny c th c cung cp nh l mt phn tch hp ca tho thun chng trnh.

6.2.2. Hng dn c th bao gm cc chi tit lin quan n cc yu t c th nh hng n vic th nghim cc mu hay vt liu th nghim c cung cp. Cc yu t ny c th bao gm: ngi trin khai, tnh cht ca mu hoc vt liu, tnh trng thit b, vic la chn quy trnh th v thi gian th nghim.

6.2.3. Hng dn c th v lp h s v bo co kt qu th nghim, hoc hiu chun cng c c cung cp (v d n v, mt s con s quan trng, c s bo co, thi hn ca kt qu,...).

6.2.4. Ngi tham gia cn c thng bo x l mu th nghim thnh tho nh l thc hin ( php th thng thng (tr khi c cc yu cu c bit v thit k ca th nghim thnh tho c yu cu lch vi nguyn tc ny).

6.3. Bao gi v vn chuyn

iu phi vin ca chng trnh cn xem xt cc kha cnh di y lin quan n vic phn phi mu th nghim hoc o. Vic bao gi v phung thc vn chuyn phi thch hp v c th bo v c nh v cc c tnh ca mu th nghim. C th c mt s hn ch nht nh trong vn chuyn ca cc quy nh v hng ho nguy him hay cc yu cu hi quan. Trong mt s trng hp, cc phng th nghim cn t chu trch nhim v vic vn chuyn mu, c bit trong cc chng trnh so snh o lng lin tip.iu phi vin cn hon thin tt c cc mu khai bo hi quan ph hp nhm m bo gim thiu s chm tr trong vic thng quan. Chng trnh cn tun th cc quy nh ca quc gia v quc t p dng cho vic vn chuyn mu th nghim.

6.4. Phn tch d liu v h s

6.4.1. Kt qu nhn c t cc phng th nghim tham gia cn c nhp v phn tch sau c bo co tr li ngay khi c th. iu thit yu l phi vn dng cc th tc kim tra hiu lc ca d liu nhp, truyn v phn tch thng k sau (xem 5.3). Lu rng cc bng d liu, cc tp tin sao lu trong my tnh, d liu in ra, biu ,... phi c lu trong mt khong thi gian xc nh.

6.4.2. Phn tch d liu cn to ra cc thc o tng hp, cc thng k c trng v thng tin km theo ph hp vi m hnh thng k v cc mc tiu ca chng trnh, cn gim thiu nh hng ca cc kt qu ngoi bin n thng k tng hp bng vic p dng cc php th pht hin gi tr bt thng nhm xc nh v sau loi b chng hoc tt nht l thng qua vic s dng k thut thng k th. Ph lc A nu cc hng dn khi qut cho vic nh gi thng k.

6.4.3. iu phi vin chng trnh cn c cc tiu ch bng vn bn x l cc kt qu th khng thch hp vi vic nh gi thnh tho. V d, khuyn ngh rng i vi cc i lng o m vt liu th nghim chng t l khng ng nht v n nh th nghim thnh tho th khng cn phn cp hay cho im.

6.5. Bo co chng trnh6.5.1. Ni dung ca bo co chng trnh s khc nhau tu thuc vo mc ch ca chng trnh c th, nhng cn r rng, d hiu v bao gm d liu v vic phn phi kt qu t tt c cc phng th nghim ng thi ch ra vic thc hin ca mi bn tham gia (xem 6.6).

6.5.2. Thng thng trong bo co chng trnh thnh tho cn c cc thng tin sau y:

a) tn v a ch ca t chc tin hnh hoc iu phi chng trnh;

b) tn v cc chi nhnh ca t chc tham gia vo vic thit k v thc hin chng trnh (xem 5.2);

c) ngy pht hnh bo co;

d) s bo co v vic nhn dng r rng chng trnh;

e) m t r mu hay vt liu s dng, bao gm c chi tit v vic chun b mu v th nghim tnh ng nht;

f) m tham gia ca phng th nghim v cc kt qu th;g) d liu thng k v cc bn tm tt, bao gm c gi tr n nh cng nh phm vi cc kt qu c th chp nhn;

h) th tc dng thit lp bt k gi tr n nh no;

i) chi tit ca vic lin kt chun v khng m bo ca mi gi tr n nh;

j) cc gi tr n nh v cc thng k tng hp v cc th tc/phng php th c s dng bi cc phng th nghim tham gia khc (nu cc phng php khc nhau c s dng bi cc phng th nghim khc nhau);

k) cc kin ca iu phi vin hay t vn k thut v vic thc hin ca phng th nghim (xem 6.6)I) th tc c s dng trong thit k, trin khai chng trnh (c th bao gm tham chiu n tha thun chng trnh);

m) th tc dng trong phn tch thng k d liu (xem Ph lc A); n) ch dn v vic gii thch phn tch thng k, nu thch hp.

6.5.3. Vi cc chng trnh c trin khai thng xuyn, cc bo co c th n gin hn ti mc nhiu yu t khuyn co trong 6.5.2 khng cn nu trong cc bo co hng ngy, tuy nhin vn c trong cc bo co tm tt nh k v khi c yu cu ca bn tham gia.

6.5.4. Cc bo co cn nhanh chng sn c trong khong thi gian quy nh. Mc d vic tt c cc d liu gc c cung cp cn c bo co cho ngi tham gia l l tng nhng trong mt s chng trnh c phm vi rt rng th c th khng lm c iu ny. Cc bn tham gia t nht cng nhn c kt qu tm tt ca tt c cc phng th nghim (v d dng biu ). Trong mt vi chng trnh nh chng trnh so snh o lng ko di cc bo co tm thi cn c pht hnh cho cc bn tham gia ring l.

6.6. nh gi vic thc hin

6.6.1. Trong trng hp cn nh gi vic thc hin, iu phi vin cn chu trch nhim m bo thch hp ca phng php nh gi nhm duy tr tin cy ca chng trnh.

6.6.2. iu phi vin c th nh s tr gip ca chuyn gia t vn k thut a ra cc kin chuyn mn v vic thc hin lin quan n:

a) vic thc hin tng th so vi cc mong i trc (tnh n khng m bo);

b) s khc nhau trong v gia cc phng th nghim (v so snh vi bt k chng trnh no trc hay d liu chnh xc c cng b);

c) s khc nhau gia cc phng php hay th tc, nu c th;

d) nguyn nhn gy sai s (lin quan n gi tr ngoi bin) v cc gi ci tin vic thc hin;e) cc gi , khuyn co hay kin chung khc;

f) kt lun.

6.6.3. C th cn phi nh k cung cp cc bng tm tt ring l cho cc bn tham gia trong sut hoc sau mt chng trnh c th. Chng c th bao gm bn tm tt c cp nht vic thc hin ca cc phng th nghim ring l cc chu trnh khc nhau ca mt chng trnh lin tc. Nhng bn tm tt ny c th phn tch chi tit hn v nu bt xu hng nu cn.

6.6.4. C nhiu th tc khc nhau nh gi vic thc hin ca cc bn tham gia, c chng trnh thc hin mt ln v sau cc chu trnh lin tip ca chng trnh lin tc. Mt s v d v cc th tc c a ra trong Ph lc A.

6.6.5. Bo co vic thc hin bng cch phn cp cc phng th nghim thnh bng theo vic thc hin ca h khng c khuyn ngh trong th nghim thnh tho. V vy, vic phn cp ch nn s dng vi s thn trng c bit v n c th lm sai lch v dn n gii thch sai.

6.7. Trao i thng tin vi cc bn tham gia

6.7.1. Cc bn tham gia cn c cung cp tp hp cc thng tin chi tit v vic tham gia chng trnh th nghim thnh tho, nh tho thun chng trnh chnh thc. Sau , vic trao i thng tin vi cc bn tham gia c th thng qua th, bn tin v/hoc bo co, cng vi cc cuc hp m rng nh k. Cc bn tham gia cn c chi dn ngay v mi thay i lin quan n thit k hay trin khai chng trnh.

6.7.2. Bn tham gia cn c kh nng lin h vi iu phi vin nu nhn thy li trong vic nh gi hot ng th nghim thnh tho.

6.7.3. Cn khuyn khch vic phn hi t cc phng th nghim cc bn tham gia ng gp tch cc vo s pht trin ca chng trnh.

6.7.4. Th tc lin quan n hnh ng khc phc ca cc bn tham gia (c bit lin quan n phn hi ti t chc cng nhn) c nu trong TCVN 7777-2 : 2008 (ISO/IEC Guide 43-2).

7. Xem xt tnh bo mt v o c ngh nghip

7.1. Bo mt h sThng thng, chnh sch ca phn ln cc chng trnh l duy tr tnh bo mt trong vic nhn dng cc bn tham gia ring. Vic nhn dng cc bn tham gia chi c mt s t ngi tham gia vo iu phi chng trnh bit, v iu ny cn m rng ti tt c cc hng dn hay cc hnh ng iu chinh tip sau p dng i vi phng th nghim th hin nng lc thc hin yu km. Trong mt s trng hp, c quan iu phi c th c yu cu bo co v vic thc hin yu km cho c quan c thm quyn c th, nhng nhng ngi tham gia cn c thng bo trc v kh nng ny khi ng tham gia chng trnh.

Mt nhm cc bn tham gia c th quyt nh t b vic bo mt trong phm vi nhm vi mc ch trao i v h tr ln nhau cng tin b.

7.2. S thng ng v lm sai lch kt qu

Mc d cc chng trnh th nghim thnh tho trc ht l nhm gip cc bn tham gia nng cao nng lc thc hin ca h, nhng gia mt s bn tham gia vn c chiu hng to n tng lc quan sai v nng lc ca h. V d vic thng ng c th xy ra gia cc phng th nghim khng a ra d liu xc thc c lp. Cc phng th nghim cng c th to n tng sai v vic thc hin khi trin khai cc phn tch c lp thng thng nhng bo co trung gian vic xc nh sao chp v cc mu th nghim thnh tho hoc tin hnh sao chp thm cc mu quy nh cho chng trnh c th. Khi c th, cc chng trnh th nghim thnh tho cn c thit k m bo rng kh nng thng ng v lm sai lch kt qu l t nht.

Mc d iu phi vin cn thc hin tt c cc bin php hp l trnh vic thng ng, nhng cng cn hiu ng rng trch nhim ca cc phng th nghim tham gia l trnh xy ra iu ny.Ph lc A

(tham kho)

Cc v d v phng php thng k dng trong x l d liu th nghim thnh tho

Cc kt qu th nghim thnh tho c th th hin di nhiu hnh thc, bao trm mt tp hp ln cc loi d liu v lm c s cho cc phn b thng k. K thut thng k s dng phn tch kt qu cn ph hp vi tng tinh hung v li qu a dng quy nh.

Tuy nhin, c ba bc ph bin i vi th nghim thnh tho khi nh gi kt qu ca cc bn tham gia:

a) xc nh gi tr n nh;

b) tnh ton cc thng k c trng;

c) nh gi vic thc hin; v trong mt s trng hp,

d) xc nh s b tnh ng nht v n nh ca mu th nghim.

Ph lc ny a ra tiu ch chung i vi cc k thut thng k c th s dng khi cn hng dn cho cc ng dng c th.

Vi nhng chng trnh so snh lin phng mi, tho thun ban u thng rt s si v c nhiu vn mi, biu mu mi, mu th nghim nhn to, tho thun v phng php s si, hoc cc th tc th nghim a dng. iu phi vin c th phi s dng cc bin php th cho vic thc hin lin quan (nh gi tr phn trm) cho ti khi tho thun c ci thin. Cc k thut thng k c th cn c sng lc khi tho thun lin phng c ci thin v th nghim thnh tho c thit lp ph hp.

Ph lc ny khng xt n cc k thut thng k i vi cc nghin cu phn tch ngoi x l d liu th nghim thnh tho. Cc k thut khc nhau cng c th cn thit thc hin cc mc ch khc ca d liu trong so snh lin phng c nu trong li gii thiu.

CH THCH: Ban k thut ISO/TC 69 hin ang son tho ti liu cung cp thng tin chi tit v cc phng php thng k nu trong ph lc ny.

A.1 Xc nh gi tr n nh v khng m bo ca cc gi tr ny

A.1.1 C nhiu th tc thit lp gi tr n nh khc nhau. Cc th tc ph bin nht c nu di y theo mt trt t m trong nhiu trng hp s lm tng khng m bo ca gi tr n nh. Cc th tc ny cn s dng:

a) Cc gi tr cho trc - vi kt qu xc nh bng cng thc ca mu th nghim c th (v d sn xut hoc iu ch).

b) Gi tr quy chiu c chng nhn - nh xc nh bng phng php cui cng (i vi cc php th nh lng).

c) Gi tr quy chiu - nh xc nh bng phn tch, o hoc so snh mu th nghim theo mu chun hay chun chnh c kh nng lin kt vi chun quc gia hoc quc t.

d) Gi tr ng thun t cc phng thi nghim chuyn nghip - cc phng th nghim chuyn nghip cn c nng lc c th hin trong vic xc nh (cc) i lng o cn th, s dng cc phng php c xc nhn gi tr s dng c chm, chnh xc cao, v c th so snh c vi nhng phng php thng s dng. Trong mt s trng hp, cc phng th nghim c th l Phng th nghim quy chiu.

e) Gi tr ng thun t cc phng th nghim tham gia - s dng k thut thng k m t trong A.1.3 vi vic xem xt nh hng ca cc gi tr ngoi bin.

A.1.2 Gi tr n nh cn c xc nh nh gi cng bng cc bn tham gia, thc y hn na tho thun lin phng v lin phng php. Vic ny c thc hin thng qua vic la chn cc nhm so snh chung, v vic s dng gi tr n nh chung khi c th.

A.1.3 Cc thng k sau y c th ph hp khi gi tr n nh c xc nh bng phng php ng thun:

a) gi tr nh tnh - s ng thun ca t l phn ln c xc nh trc (thng c th hin theo thang o danh ngha hoc th t);

b) gi tr nh lng - "gi tr trung bnh i vi nhm so snh ph hp nh l:

i) gi tr trung bnh c th c ly trng s hay chuyn i (v d trung bnh rt gn hoc trung bnh nhn),

ii) trung v, mt (mode) hoc php o th khc.

A.1.4 khng m bo ca gi tr n nh cn c xc nh bng cch s dng cc th tc m t trong Hng dn th hin khng m bo o khi thch hp.

A.1.5 Cc kt qu ngoi bin c x l nh di y.

a) Khi kt qu ca cc bn tham gia c dng xc nh gi tr n nh, cc k thut cn thch hp hn ch ti a nh hng ca kt qu ngoi bin. Vic ny cn c thc hin cng phng php thng k th hoc bng cch loi b cc gi tr bt thng trc khi tnh ton (xem ISO 5725-2). Trong cc chng trnh ln hn hoc chng trnh thng thng, c th c bng hin th gi tr bt thng t ng.

b) Nu cc kt qu c loi b nh cc gi tr bt thng, th chi nn loi b cho vic tnh ton thng k tng hp. Cc kt qu ny vn cn c nh gi trong chng trnh thnh tho v phi c a ra phn loi thc hin thch hp.

A.1.6 Cc xem xt khc c tin hnh nh di y:

a) L tng l xc nh gi tr n nh bng cch quy chiu hoc s ng thun ca cc bn tham gia, iu phi vin cn c th tc xc nh ng ca gi tr n nh v xem xt vic phn b d liu.

b) iu phi vin cn c tiu ch chp nhn gi tr n nh theo khng m bo ca n.

A.2 Tnh ton thng k c trng A.2.1 Thc hin trn mu th nghim n l

A.2.1.1 Kt qu th nghim thnh tho thng cn phi chuyn i sang mt thng k c trng h tr vic gii thch v cho php so snh vi mc tiu xc nh. Mc ch l o lch so vi gi tr n nh theo cch cho php so snh vi tiu ch c trng. Cc k thut c th t khng yu cu x l n cc chuyn i thng k phc tp.

A.2.1.2 Cc bin php thc hin cn c ngha i vi cc bn tham gia chng trnh. V vy, cc thc o cn lin quan n nhu cu ng dng ca php th v c thu hiu hoc c tnh truyn thng trong mt lhh vc c th.

A.2.1.3 Cc thc o s thay i thng c s dng tnh ton thng k c trng v trong bo co tm tt chng trnh th nghim thnh tho. V d ph bin v cc thc o s thay i i vi nhm so snh thch hp bao gm:

a) lch chun (SD);

b) h s bin thin (CV) hoc lch chun tng i (RSD);

c) cc phn v, lch tuyt i ca trung v hoc cc thc o th khc.

A.2.1.4 i vi cc kt qu nh tnh, vic tnh ton thng khng cn thit.

Cc thng k thng c s dng cho nhng kt qu nh lng c lit k di y theo mc bin i kt qu tng dn ca cc bn tham gia.

a) Hiu s (x-X), trong "x" l kt qu ca bn tham gia v "X" l gi tr n nh.

b) Chnh lch theo phn trm,

c) Phn v hoc dy

d) T s z, trong

z =

v s l bin c lng/thc o thch hp ca s thay i c chn ph hp vi cc yu cu ca chng trnh. Cng thc ny c th c s dng trong cc trng hp khi X v s c c t kt qu ca cc bn tham gia hay khi X v s khng c c t (tt c) cc kt qu ca bn tham gia. [V d khi gi tr n nh v s thay i c quy nh; tham kho 4.2 ca Tho thun hi ho quc t v th nghim thnh tho ca Phng thi nghim phn tch (ho hc)]e) S En (thng s dng c th trong chng trnh so snh o lng), trong

v Ulab l khng m bo ca kt qu ca bn tham gia v Uref l khng m bo ca gi tr n nh ca phng th nghim quy chiu.

A.2.1.5 Cc xem xt nh nu di y.

a) S khc bit khng ng k gia kt qu ca bn tham gia v gi tr n nh c th thch hp xc nh c trng v c ngi tham gia hiu mt cch d dng nht. Tr s (x-X) trong TCVN 6910-4 : 2001 (ISO 5725-4) c gi l c lng chch phng th nghim".

b) Cc iu chinh phn trm chnh lch i vi nng v c cc bn tham gia thu hiu.

c) Cc phn v hoc dy l hu ch vi cc kt qu phn tn cao hoc kt qu lch, cc p ng theo th t hoc khi c mt s gii hn cc p ng khc nhau. K thut ny cn c s dng thn trng (xem 6.6.5).

d) Kt qu chuyn i c th c u tin, hoc cn thit, tu thuc vo bn cht ca php th. V d cc kt qu da trn s pha long l mt dng ca thang hnh hc, c th chuyn i theo logarit.

e) Nu s dng tiu ch thng k (v d t s z), c lng ca s thay i phi ng tin cy; l trn c s cc quan trc y nhm lm gim nh hng ca cc gi tr ngoi bin v t c khng m bo thp.

A.2.2 T s c trng phi hp

A.2.2.1 c trng c th c nh gi trn c s nhiu hn mt kt qu trong mt chu trnh th nghim thnh tho n l. iu ny xy ra khi c nhiu hn mt mu th nghim cho mt i lng o c th, hoc mt h i lng o lin quan. Vic ny c thc hin a ra nh gi c trng ton din hn.

Cc phng php th nh Biu Youden hay th biu din thng k h ca Mandel l cc k thut hiu qu din t c trng (xem TCVN 6910-2:2001 (ISO 5725-2)).

Cc v d c nu di y:

a) T s kt hp i vi cng mt i lng o:

- s lng kt qu tho mn;

- t s z trung bnh hoc tng cng;

- hiu s tuyt i trung bnh (theo n v hoc phn trm);

- hiu s tuyt i tng (hay hiu bnh phng);

b) T s kt hp i vi cc i lng o khc nhau:

- s lng (hoc phn trm) kt qu tho mn;

- t s z trung bnh tuyt i;

- hiu tuyt i trung bnh so vi gii hn nh gi.

A.2.2.2 Cc xem xt nh nu di y:

a) T s c th c chuyn i (nu cn) tt c cng theo mt phn b gi nh (v d phn b Gau-x cho t s z hay X2 cho hiu bnh phng).

b) Cn kim tra gi tr ngoi bin c th c nh hng ln ti t s kt hp nh lng.

A.3 nh gi vic thc hin A.3.1 Thc hin ban u

Tiu ch nh gi vic thc hin cn c thit lp sau khi xem xt cc thc o hot ng c lin quan n cc c trng nht nh hay khng.

A.3.1.1 Cc c trng ny nh sau:a) S ng thun chuyn mn: khi nhm t vn hoc cc chuyn gia lnh ngh khc quyt nh trc tip vic kt qu bo co c ph hp vi mc ch hay khng. S ng thun chuyn mn l cch thc in hnh nh gi kt qu ca cc php th nh tnh.

b) Tnh ph hp vi mc ch: v d, xem xt cc quy nh v thc hin phng php v trnh iu hnh c cng nhn ca cc bn tham gia.

c) Xc nh t s bng thng k: trong cc tiu ch cn ph hp vi tng t s. V d ph bin v ng dng t s l:

i) vi t s z:

|z|< 2 = tho mn

2