Introduction to biostatistics
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Transcript of Introduction to biostatistics
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June 22, 2013 Dr Fayssal Farahat, MD 1
Dr. Fayssal M Farahat, MBBCh, MSc, PhD
Consultant Public Health
Infection Prevention and Control
King AbdulAziz Medical City–Jeddah
National Guard Health Affairs
Descriptive Statistics
June 22, 2013 Dr Fayssal Farahat, MD 2
“Whatever you can not measure, you can not
manage”
June 22, 2013 Dr Fayssal Farahat, MD 3
Statistics business education psychology
Biology and Medicine
Biostatistics
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June 22, 2013 Dr Fayssal Farahat, MD 4
Statistics
Collection Presentation Analysis
Draw inferences
June 22, 2013 Dr Fayssal Farahat, MD 5
Data = numbers
Measurement Counting
A nurse takes a
patient’s
temperature
A hospital
administrator counts
number of discharged
patients on a given
day.
June 22, 2013 Dr Fayssal Farahat, MD 6
Data
Data
Data
Data
Decision
The procedure by
which we reach a
conclusion about a
population on the
basis of information
contained in a sample
drawn from this
population
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June 22, 2013 Dr Fayssal Farahat, MD 7
Students’ scores:
75, 95, 60, 93, 85, 84, 76, 92, 62, 83,
80, 90, 64, 75,79, 32, 78, 64, 98,
73,88, 61, 82, 86, 79, 78, 80, 55
How useful would that list of number be to you?
How to get information out of data …
FIRST STEP, the data have to be organized and Summarized.
Data INFO
June 22, 2013 Dr Fayssal Farahat, MD 8
Sources of Data
Primary Data Collection & Analysis
Secondary Data Collection & Analysis
Client satisfaction & Identification Surveys
Lifestyle and health behavior surveys
Focus Group discussions
Hospital Records
inpatients outpatients Birth Death
External sources (published reports)
June 22, 2013 Dr Fayssal Farahat, MD 9
Measurement
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June 22, 2013 Dr Fayssal Farahat, MD 10
Variable
=
Characteristic not the same when observed in different possessors.
June 22, 2013 Dr Fayssal Farahat, MD 11
VARIABLES
June 22, 2013 Dr Fayssal Farahat, MD 12
Quantitative
Discrete
منفصلة
No fractions
ال كسور عشرية
Continuous
متصلة
Fractions
كسور عشرية
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June 22, 2013 Dr Fayssal Farahat, MD 13
Qualitative
Ordinal
ترتيبية
Nominal
اسمية
June 22, 2013 Dr Fayssal Farahat, MD 14
Discrete
منفصلة
• Number of pregnancies • Number of children • Family size • Heart rate • Respiratory rate • Number of cigarettes
June 22, 2013 Dr Fayssal Farahat, MD 15
Continuous
متصلة• WEIGHT
• HIGHT
• AGE
• TEPERATURE
• BLOOD PRESSURE
• RBS
• AMOUNT OF URINE
• BODY SURFACE AREA
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June 22, 2013 Dr Fayssal Farahat, MD 16
Nominal
- Gender : " Male – female . "
- Marital status: married, single, widow, divorced
(1) (2)
(1) (2) (3) (4)
June 22, 2013 Dr Fayssal Farahat, MD 17
Ordinal
- grade : " A+ A B+ B C+ C D+ D "
.
- Educational level: 1ry, 2ry, university
- Income: < 5000, 5000-10.000, >10.000
(1) (2) (3) (4) (5) (6) (7)
(1) (2) (3)
(1) (2) (3)
June 22, 2013 Dr Fayssal Farahat, MD 18
Quantitative
Qualitative
High systole
Qualitative
x
Quantitative
200 x
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June 22, 2013 Dr Fayssal Farahat, MD 19
Measurement Scales
Nominal
Ordinal
Interval
Ratio
June 22, 2013 Dr Fayssal Farahat, MD 20
Temperature
True
zero
Weight
June 22, 2013 Dr Fayssal Farahat, MD 21
The distinction is not about
the value, but the association,
causality each variable
occupies in the equation.
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June 22, 2013 Dr Fayssal Farahat, MD 22
Frequency table
الجدول التكراري
Interval
الفترة
Frequency
التكرار
Valid %
النسبة المئوية
Cumulative %
النسبة التراكمية<20
20-29
30-39
40-49
50-59
60-69
70-79
80-89
≥90
Total
46
70
108
106
74
72
42
29
33
580
7.9
12.1
18.6
18.3
12.8
12.4
7.2
5.0
5.7
100.0
7.9
20.0
38.6
56.9
69.7
82.1
89.3
94.3
100
Few
6-14
Overlap 40-49, 49-50
Equal width
Avoid
open-ended Cumulative %=
Obs % + all lower %
<60
June 22, 2013 Dr Fayssal Farahat, MD 23
City Male smokers المدخنون
Taif
Riyadh
Jeddah
TOTAL
Table (1). Number and percent of male smokers
less and more than 18 ys old in different cities
< 18 years > 18 years n % n %
80
90
150
320
TOTAL
n %
40
30
30
32
120
210
350
680
60
70
70
68
200 100
300
500
1000
100
100
100
Tables
June 22, 2013 Dr Fayssal Farahat, MD 24
Tables
City Male smokers
Taif
Riyadh
Jeddah
TOTAL
Table (1). Number and percent of male smokers
less and more than 18 ys old in different cities
< 18 years > 18 years
n % n %
80
90
150
320
TOTAL
n %
25
28
47
100
120
210
350
680
18
31
51
100
200 20
300
500
1000
30
50
100
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June 22, 2013 Dr Fayssal Farahat, MD 25
2 x 2
Exposure
Smoker
Non-smoker
Cancer Lung Positive
N (%)
Negative
N (%)
June 22, 2013 Dr Fayssal Farahat, MD 26
Graphs
Line graph
Frequency Histogram
Frequency polygon
Bar chart
Pie chart
Pictogram
June 22, 2013 Dr Fayssal Farahat, MD 27
Time
Positive
No relation
Negative
Vari
ab
le
X
Y
+
-
0
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June 22, 2013 Dr Fayssal Farahat, MD 28
X
Y
Equal width
June 22, 2013 Dr Fayssal Farahat, MD 29
Frequency Polygone
المنحنى التكراري
June 22, 2013 Dr Fayssal Farahat, MD 30
heal thy disease
group
2
4
6
8
10
Coun
t
Healthy Diseased
Co
un
t
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June 22, 2013 Dr Fayssal Farahat, MD 31
39.7
58.8
gp 1
gp 2
Age
June 22, 2013 Dr Fayssal Farahat, MD 32
Sex distribution in different studied groups
0
10
20
30
40
50
60
70
80
Control Asthmatic COPD
%
Male
Female
June 22, 2013 Dr Fayssal Farahat, MD 33
healthydisease
group
Pies show countsPie
44.44%8.055.56%
10.0
Pie Chart
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June 22, 2013 Dr Fayssal Farahat, MD 34
Pictogram
1970 1980 1990 2000
June 22, 2013 Dr Fayssal Farahat, MD 35
0
2
4
6
8
10
12
14
Y1950 Y1960 Y1970 Y1980 Y1990 Y2000
Year
Mo
rta
lity
(p
er 1
00
0)
2
4
6
8
10
12
14
0
1
2
3
4
1970y 1980y 1990y 2000y
June 22, 2013 Dr Fayssal Farahat, MD 36
Summarizing qualitative data
Proportion
a / a + b (part / whole)
Percentage Proportion X 100%
Ratio
a / b (part / another part)
Rate a / a + b X base (1000, 10,000,100,000) + In a specific time (20 per 10,000 per year)
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June 22, 2013 Dr Fayssal Farahat, MD 37
Arithmetic Mean
Extremes HR
variation
1
2
3
4
5
6
7
8
9
10
19.2
51.9
33.1
86.7
29.1
45.3
16.4
85.7
18.9
42.6
42.9
32.1
Consider each variable
X
June 22, 2013 Dr Fayssal Farahat, MD 38
Weighted Mean
Interval Frequency Valid % Cumulative %
2-20
21-30
31-40
41-50
51-60
61-70
71-80
81-90
>90
Total
46
70
108
106
74
72
42
29
33
580
7.9
12.1
18.6
18.3
12.8
12.4
7.2
5.0
5.7
100.0
7.9
20.0
38.6
56.9
69.7
82.1
89.3
94.3
100
[(11 x 46) + (25 x 70) + ….+ (85 x 29) + (100 x 33)] / 580 = 49.1
X
?
June 22, 2013 Dr Fayssal Farahat, MD 39
Median Middle observation
Odd Even
Extremes Consider each variable
Ordinal data
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June 22, 2013 Dr Fayssal Farahat, MD 40
Mode
Most frequent value
Uni-modal Bi-modal
Most frequent interval
Most frequent diagnosis
June 22, 2013 Dr Fayssal Farahat, MD 41
Measures of Spread
مقاييس التشتت
Range SD CV
Percentiles Interquartile
Range
المدى االنحراف المعياري
معامل التغير
Percentiles
المدى الربعي
June 22, 2013 Dr Fayssal Farahat, MD 42
The Range
The largest – the smallest
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June 22, 2013 Dr Fayssal Farahat, MD 43
June 22, 2013 Dr Fayssal Farahat, MD 44
Coefficient of Variation
معامل التغير
Measure 1 70 (31)
Measure 2 105 (48)
Can
we
Compare
2 different scales
2 different investigators
CV = (SD / Mean) x 100
44.3 % 45.7 %
Quality
Control
June 22, 2013 Dr Fayssal Farahat, MD 45
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June 22, 2013 Dr Fayssal Farahat, MD 46
Interquartile Range
المدى الربعي
= the difference between the 25th and 75th percentiles
25th 75th
Central 50%
6.5 kg 7.5 kg
1st 3rd
June 22, 2013 Dr Fayssal Farahat, MD 47
STEM
الساق
LEAF
الورقة
2
3
4
5
6
5689
0011369
0269
03
027
30.00
33.00
31.00
29.00
30.00
31.00
26.00
28.00
36.00
39.00
40.00
49.00
50.00
60.00
67.00
46.00
42.00
25.00
62.00
53.00
Stem and Leaf Plot
June 22, 2013 Dr Fayssal Farahat, MD 48
Box – and whisker plot
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June 22, 2013 Dr Fayssal Farahat, MD 49
Normal Distribution Curve
Gaussian Distribution Curve
June 22, 2013 Dr Fayssal Farahat, MD 50
Mean
Median
Mode
Bell Shape
68%
Symmetric
June 22, 2013 Dr Fayssal Farahat, MD 51
Mean
Median
Mode
Bell Shape
95%
Symmetric
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Normal curves
(μ=0, σ2=1) and (μ=5, σ 2=1)
-2 0 2 4 6 8
x
0.0
0.1
0.2
0.3
0.4
fx1
Normal curves (μ=0, σ2=1) and (μ=0, σ2=2)
-3 -2 -1 0 1 2 3
x
0.0
0.1
0.2
0.3
0.4
y
Normal curves (μ=0, σ2=1) and (μ=2, σ2=0.25)
-2 0 2 4 6 8
x
0.0
0.2
0.4
0.6
0.8
1.0
fx1
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June 22, 2013 Dr Fayssal Farahat, MD 55
80 90 100 110 120 130 140 150 160
0
5
10
15
20
25
P e r c e n t
POUNDS
120 130 110
68% of 100 = .68 x 100 = ~ 68 students
80 90 100 110 120 130 140 150 160
0
5
10
15
20
25
P e r c e n t
POUNDS
120 100
95% of 100 = .95 x 120 = ~ 95 students
140 130 110
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80 90 100 110 120 130 140 150 160
0
5
10
15
20
25
P e r c e n t
POUNDS
120 100 140 130 110
0 +1 +2 -1 -2
X
Z
130 – 120
10
x – μ
σ
80 90 100 110 120 130 140 150 160
0
5
10
15
20
25
P e r c e n t
POUNDS
120 100 140 130 110
126
0 +1 +2 -1 -2
x – μ
σ
Looking up probabilities in the
standard normal table
Z=0.60
Z=0.00
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What is the area to the left of Z=1.51 in a standard normal curve?
Z=1.51
Z=1.51
Area is 93.45%