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![Page 1: Development of Trend Analysis Guidelines at NCHS · PDF fileDevelopment of Trend Analysis Guidelines at NCHS Donald Malec Associate Director of Science O ce of Research and Methodology](https://reader030.fdocuments.net/reader030/viewer/2022032613/5a78cb407f8b9a70238c8644/html5/thumbnails/1.jpg)
Development of Trend Analysis Guidelines atNCHS
Donald MalecAssociate Director of Science
Office of Research and Methodologyand
Spokesperson, NCHS Trends Analysis Workgroup
Presentation for the Board of Scientific CounselorsSeptember 25, 2015
![Page 2: Development of Trend Analysis Guidelines at NCHS · PDF fileDevelopment of Trend Analysis Guidelines at NCHS Donald Malec Associate Director of Science O ce of Research and Methodology](https://reader030.fdocuments.net/reader030/viewer/2022032613/5a78cb407f8b9a70238c8644/html5/thumbnails/2.jpg)
Guidance being developed by NCHS workgroup
I Members include analysts across NCHSI Draft guidance document in two main parts: Guidance and
Real Examples
1. Overview of Key Trend Analysis Issues2. Choosing a Method for Trend Analysis3. Illustrative Examples of Trend Analysis with Alternative
Comparisons4. Technical Appendixes... with explanation of statistical
guidance
![Page 3: Development of Trend Analysis Guidelines at NCHS · PDF fileDevelopment of Trend Analysis Guidelines at NCHS Donald Malec Associate Director of Science O ce of Research and Methodology](https://reader030.fdocuments.net/reader030/viewer/2022032613/5a78cb407f8b9a70238c8644/html5/thumbnails/3.jpg)
●●
●
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●
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010
2030
4050
NHANES Cycle
perc
ent
1999−2000 2001−2002 2003−2004 2005−2006 2007−2008 2009−2010
An example of a trend
Figure : Prevalence of Obesity among adults age 60 years and older,NHANES 1999-2010.
![Page 4: Development of Trend Analysis Guidelines at NCHS · PDF fileDevelopment of Trend Analysis Guidelines at NCHS Donald Malec Associate Director of Science O ce of Research and Methodology](https://reader030.fdocuments.net/reader030/viewer/2022032613/5a78cb407f8b9a70238c8644/html5/thumbnails/4.jpg)
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010
2030
4050
NHANES Cycle
perc
ent
1999−2000 2001−2002 2003−2004 2005−2006 2007−2008 2009−2010
An example of a trend
Figure : Prevalence of Obesity among adults age 60 years and older,NHANES 1999-2010.
![Page 5: Development of Trend Analysis Guidelines at NCHS · PDF fileDevelopment of Trend Analysis Guidelines at NCHS Donald Malec Associate Director of Science O ce of Research and Methodology](https://reader030.fdocuments.net/reader030/viewer/2022032613/5a78cb407f8b9a70238c8644/html5/thumbnails/5.jpg)
ll
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010
2030
4050
NHANES Cycle
perc
ent
1999−2000 2001−2002 2003−2004 2005−2006 2007−2008 2009−2010
An example of a trend
Figure : Prevalence of Obesity among adults age 60 years and older,NHANES 1999-2010.
![Page 6: Development of Trend Analysis Guidelines at NCHS · PDF fileDevelopment of Trend Analysis Guidelines at NCHS Donald Malec Associate Director of Science O ce of Research and Methodology](https://reader030.fdocuments.net/reader030/viewer/2022032613/5a78cb407f8b9a70238c8644/html5/thumbnails/6.jpg)
l l l l ll l l l l
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2000 2002 2004 2006 2008 2010 2012
010
2030
4050
Year
perc
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PrivateMedicaidUninsured
other examples of trends ...
Figure : Percent of persons with any emergency room use in the past 12months among adults aged 18-64, by insurance status. NHIS 2000-2013.
![Page 7: Development of Trend Analysis Guidelines at NCHS · PDF fileDevelopment of Trend Analysis Guidelines at NCHS Donald Malec Associate Director of Science O ce of Research and Methodology](https://reader030.fdocuments.net/reader030/viewer/2022032613/5a78cb407f8b9a70238c8644/html5/thumbnails/7.jpg)
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2005 2006 2007 2008 2009 2010 2011
05
1015
2025
Year
Perc
ent o
f Vis
its
other examples of trends ...
Figure : Percentage of ED visits in which an EKG was ordered orprovided: United States. NHAMCS 2005-2011.
![Page 8: Development of Trend Analysis Guidelines at NCHS · PDF fileDevelopment of Trend Analysis Guidelines at NCHS Donald Malec Associate Director of Science O ce of Research and Methodology](https://reader030.fdocuments.net/reader030/viewer/2022032613/5a78cb407f8b9a70238c8644/html5/thumbnails/8.jpg)
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1995 2000 2005 2010
020
4060
8010
0
Year
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Age 15−17Age 18−19
other examples of trends ...
Figure : Birth rates for women aged 15-17 and 18-19: United States,1991-2013.
![Page 9: Development of Trend Analysis Guidelines at NCHS · PDF fileDevelopment of Trend Analysis Guidelines at NCHS Donald Malec Associate Director of Science O ce of Research and Methodology](https://reader030.fdocuments.net/reader030/viewer/2022032613/5a78cb407f8b9a70238c8644/html5/thumbnails/9.jpg)
Aim of a Guidance Document for Trend Analysis
I Focus on descriptive statistics, not prediction
I Document issues that may cause controversy - choice ofstudy interval, choice of model, etc.
I Provide a summary of methods for reference
I When possible, suggest a preferred method
![Page 10: Development of Trend Analysis Guidelines at NCHS · PDF fileDevelopment of Trend Analysis Guidelines at NCHS Donald Malec Associate Director of Science O ce of Research and Methodology](https://reader030.fdocuments.net/reader030/viewer/2022032613/5a78cb407f8b9a70238c8644/html5/thumbnails/10.jpg)
Aim of a Guidance Document for Trend Analysis
I Focus on descriptive statistics, not prediction
I Document issues that may cause controversy - choice ofstudy interval, choice of model, etc.
I Provide a summary of methods for reference
I When possible, suggest a preferred method
I Recognize limitations of rules
I Analyst will bring expertise into the analysisI Include “just enough detail”
![Page 11: Development of Trend Analysis Guidelines at NCHS · PDF fileDevelopment of Trend Analysis Guidelines at NCHS Donald Malec Associate Director of Science O ce of Research and Methodology](https://reader030.fdocuments.net/reader030/viewer/2022032613/5a78cb407f8b9a70238c8644/html5/thumbnails/11.jpg)
Why are trends analyzed at NCHS? .... here are a few
I Topical ... trends in obesity prevalence
I Program changes ... trends in health insurance coverage
I Surveillance/ resource ... Health US and Healthy People
I Interesting changes (e.g. changes in slope) noted byanalysts
![Page 12: Development of Trend Analysis Guidelines at NCHS · PDF fileDevelopment of Trend Analysis Guidelines at NCHS Donald Malec Associate Director of Science O ce of Research and Methodology](https://reader030.fdocuments.net/reader030/viewer/2022032613/5a78cb407f8b9a70238c8644/html5/thumbnails/12.jpg)
First step: How are trends analyzed at NCHS now?
I Linear regression (straight line)
I Comparison to a benchmark year
I Linear (with curves) and non-linear regression
![Page 13: Development of Trend Analysis Guidelines at NCHS · PDF fileDevelopment of Trend Analysis Guidelines at NCHS Donald Malec Associate Director of Science O ce of Research and Methodology](https://reader030.fdocuments.net/reader030/viewer/2022032613/5a78cb407f8b9a70238c8644/html5/thumbnails/13.jpg)
First step: How are trends analyzed at NCHS now?
I Linear regression (straight line)I least squares fit to population prevalence
I Comparison to a benchmark year
I Linear (with curves) and non-linear regression
![Page 14: Development of Trend Analysis Guidelines at NCHS · PDF fileDevelopment of Trend Analysis Guidelines at NCHS Donald Malec Associate Director of Science O ce of Research and Methodology](https://reader030.fdocuments.net/reader030/viewer/2022032613/5a78cb407f8b9a70238c8644/html5/thumbnails/14.jpg)
First step: How are trends analyzed at NCHS now?
I Linear regression (straight line)I least squares fit to population prevalenceI population weighted least squares fit to population prevalence
I Comparison to a benchmark year
I Linear (with curves) and non-linear regression
I sample variance weighted least squares fit to populationprevalence
I In 2013, 17.8% of noninstitutionalized adults aged 18 and overwere current cigarette smokers, a decline from 2000 (2014 -HUS)
I polynomial regression ... orthogonal polynomialsI linear splines ... joinpoint software (NCI)I log transform, logistic transform of prevalence ratesI smoothing by collapsing years, followed by additional analysisI pairwise comparisons
![Page 15: Development of Trend Analysis Guidelines at NCHS · PDF fileDevelopment of Trend Analysis Guidelines at NCHS Donald Malec Associate Director of Science O ce of Research and Methodology](https://reader030.fdocuments.net/reader030/viewer/2022032613/5a78cb407f8b9a70238c8644/html5/thumbnails/15.jpg)
First step: How are trends analyzed at NCHS now?
I Linear regression (straight line)I least squares fit to population prevalenceI population weighted least squares fit to population prevalenceI sample variance weighted least squares fit to population
prevalence
I Comparison to a benchmark year
I Linear (with curves) and non-linear regression
![Page 16: Development of Trend Analysis Guidelines at NCHS · PDF fileDevelopment of Trend Analysis Guidelines at NCHS Donald Malec Associate Director of Science O ce of Research and Methodology](https://reader030.fdocuments.net/reader030/viewer/2022032613/5a78cb407f8b9a70238c8644/html5/thumbnails/16.jpg)
First step: How are trends analyzed at NCHS now?
I Linear regression (straight line)I least squares fit to population prevalenceI population weighted least squares fit to population prevalenceI sample variance weighted least squares fit to population
prevalence
I Comparison to a benchmark yearI In 2013, 17.8% of noninstitutionalized adults aged 18 and over
were current cigarette smokers, a decline from 2000 (2014 -HUS)
I Linear (with curves) and non-linear regression
![Page 17: Development of Trend Analysis Guidelines at NCHS · PDF fileDevelopment of Trend Analysis Guidelines at NCHS Donald Malec Associate Director of Science O ce of Research and Methodology](https://reader030.fdocuments.net/reader030/viewer/2022032613/5a78cb407f8b9a70238c8644/html5/thumbnails/17.jpg)
First step: How are trends analyzed at NCHS now?
I Linear regression (straight line)I least squares fit to population prevalenceI population weighted least squares fit to population prevalenceI sample variance weighted least squares fit to population
prevalence
I Comparison to a benchmark yearI In 2013, 17.8% of noninstitutionalized adults aged 18 and over
were current cigarette smokers, a decline from 2000 (2014 -HUS)
I Linear (with curves) and non-linear regressionI polynomial regression ... orthogonal polynomials
![Page 18: Development of Trend Analysis Guidelines at NCHS · PDF fileDevelopment of Trend Analysis Guidelines at NCHS Donald Malec Associate Director of Science O ce of Research and Methodology](https://reader030.fdocuments.net/reader030/viewer/2022032613/5a78cb407f8b9a70238c8644/html5/thumbnails/18.jpg)
First step: How are trends analyzed at NCHS now?
I Linear regression (straight line)I least squares fit to population prevalenceI population weighted least squares fit to population prevalenceI sample variance weighted least squares fit to population
prevalence
I Comparison to a benchmark yearI In 2013, 17.8% of noninstitutionalized adults aged 18 and over
were current cigarette smokers, a decline from 2000 (2014 -HUS)
I Linear (with curves) and non-linear regressionI polynomial regression ... orthogonal polynomialsI linear splines ... joinpoint software (NCI)
![Page 19: Development of Trend Analysis Guidelines at NCHS · PDF fileDevelopment of Trend Analysis Guidelines at NCHS Donald Malec Associate Director of Science O ce of Research and Methodology](https://reader030.fdocuments.net/reader030/viewer/2022032613/5a78cb407f8b9a70238c8644/html5/thumbnails/19.jpg)
First step: How are trends analyzed at NCHS now?
I Linear regression (straight line)I least squares fit to population prevalenceI population weighted least squares fit to population prevalenceI sample variance weighted least squares fit to population
prevalence
I Comparison to a benchmark yearI In 2013, 17.8% of noninstitutionalized adults aged 18 and over
were current cigarette smokers, a decline from 2000 (2014 -HUS)
I Linear (with curves) and non-linear regressionI polynomial regression ... orthogonal polynomialsI linear splines ... joinpoint software (NCI)I log transform, logistic transform of prevalence rates
![Page 20: Development of Trend Analysis Guidelines at NCHS · PDF fileDevelopment of Trend Analysis Guidelines at NCHS Donald Malec Associate Director of Science O ce of Research and Methodology](https://reader030.fdocuments.net/reader030/viewer/2022032613/5a78cb407f8b9a70238c8644/html5/thumbnails/20.jpg)
First step: How are trends analyzed at NCHS now?
I Linear regression (straight line)I least squares fit to population prevalenceI population weighted least squares fit to population prevalenceI sample variance weighted least squares fit to population
prevalence
I Comparison to a benchmark yearI In 2013, 17.8% of noninstitutionalized adults aged 18 and over
were current cigarette smokers, a decline from 2000 (2014 -HUS)
I Linear (with curves) and non-linear regressionI polynomial regression ... orthogonal polynomialsI linear splines ... joinpoint software (NCI)I log transform, logistic transform of prevalence ratesI smoothing by collapsing years, followed by additional analysis
![Page 21: Development of Trend Analysis Guidelines at NCHS · PDF fileDevelopment of Trend Analysis Guidelines at NCHS Donald Malec Associate Director of Science O ce of Research and Methodology](https://reader030.fdocuments.net/reader030/viewer/2022032613/5a78cb407f8b9a70238c8644/html5/thumbnails/21.jpg)
First step: How are trends analyzed at NCHS now?
I Linear regression (straight line)I least squares fit to population prevalenceI population weighted least squares fit to population prevalenceI sample variance weighted least squares fit to population
prevalence
I Comparison to a benchmark yearI In 2013, 17.8% of noninstitutionalized adults aged 18 and over
were current cigarette smokers, a decline from 2000 (2014 -HUS)
I Linear (with curves) and non-linear regressionI polynomial regression ... orthogonal polynomialsI linear splines ... joinpoint software (NCI)I log transform, logistic transform of prevalence ratesI smoothing by collapsing years, followed by additional analysisI pairwise comparisons
![Page 22: Development of Trend Analysis Guidelines at NCHS · PDF fileDevelopment of Trend Analysis Guidelines at NCHS Donald Malec Associate Director of Science O ce of Research and Methodology](https://reader030.fdocuments.net/reader030/viewer/2022032613/5a78cb407f8b9a70238c8644/html5/thumbnails/22.jpg)
l
l
l
l
l
1 2 3 4 5
910
1112
1314
period
perc
ent
Methodological Issues: Design vs Model-based Approach
![Page 23: Development of Trend Analysis Guidelines at NCHS · PDF fileDevelopment of Trend Analysis Guidelines at NCHS Donald Malec Associate Director of Science O ce of Research and Methodology](https://reader030.fdocuments.net/reader030/viewer/2022032613/5a78cb407f8b9a70238c8644/html5/thumbnails/23.jpg)
l
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1 2 3 4 5
910
1112
1314
period
perc
ent
SUDAAN DESCRIPTSAS WLS & Joinpoint
Methodological Issues: Design vs Model-based Approach
I Trend estimates are similar but significance can vary widely
![Page 24: Development of Trend Analysis Guidelines at NCHS · PDF fileDevelopment of Trend Analysis Guidelines at NCHS Donald Malec Associate Director of Science O ce of Research and Methodology](https://reader030.fdocuments.net/reader030/viewer/2022032613/5a78cb407f8b9a70238c8644/html5/thumbnails/24.jpg)
l
l
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l
l
1 2 3 4 5
910
1112
1314
period
perc
ent
p−value=0.033
p−value=0.285
SUDAAN DESCRIPTSAS WLS & Joinpoint
Methodological Issues: Design vs Model-based Approach
I Trend estimates are similar but significance can vary widely
![Page 25: Development of Trend Analysis Guidelines at NCHS · PDF fileDevelopment of Trend Analysis Guidelines at NCHS Donald Malec Associate Director of Science O ce of Research and Methodology](https://reader030.fdocuments.net/reader030/viewer/2022032613/5a78cb407f8b9a70238c8644/html5/thumbnails/25.jpg)
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1 2 3 4 5
910
1112
1314
period
perc
ent
p−value=0.033SE=.45
p−value=0.285SE=.52
SUDAAN DESCRIPTSAS WLS & Joinpoint
Methodological Issues: Design vs Model-based Approach
I Trend estimates are similar but significance can vary widely
![Page 26: Development of Trend Analysis Guidelines at NCHS · PDF fileDevelopment of Trend Analysis Guidelines at NCHS Donald Malec Associate Director of Science O ce of Research and Methodology](https://reader030.fdocuments.net/reader030/viewer/2022032613/5a78cb407f8b9a70238c8644/html5/thumbnails/26.jpg)
l
l
l
l
l
1 2 3 4 5
910
1112
1314
period
perc
ent
p−value=0.033
DF~80SE=.45
p−value=0.285
DF=4SE=.52
SUDAAN DESCRIPTSAS WLS & Joinpoint
Methodological Issues: Design vs Model-based Approach
I Trend estimates are similar but significance can vary widely
![Page 27: Development of Trend Analysis Guidelines at NCHS · PDF fileDevelopment of Trend Analysis Guidelines at NCHS Donald Malec Associate Director of Science O ce of Research and Methodology](https://reader030.fdocuments.net/reader030/viewer/2022032613/5a78cb407f8b9a70238c8644/html5/thumbnails/27.jpg)
l
l
l
l
l
1 2 3 4 5
910
1112
1314
period
perc
ent
p−value=0.033
DF~80SE=.45
p−value=0.285
DF=4SE=.52
SUDAAN DESCRIPTSAS WLS & Joinpoint
Methodological Issues: Design vs Model-based Approach
I Trend estimates are similar but significance can vary widely
I Model-based includes “lack of model fit” as error.Design-based provides variance of each point estimate.
![Page 28: Development of Trend Analysis Guidelines at NCHS · PDF fileDevelopment of Trend Analysis Guidelines at NCHS Donald Malec Associate Director of Science O ce of Research and Methodology](https://reader030.fdocuments.net/reader030/viewer/2022032613/5a78cb407f8b9a70238c8644/html5/thumbnails/28.jpg)
Methodological Issues: What Slope to Estimate?
I Not the usual issue of how to estimate (i.e. efficiency) but,rather, what to estimate
I When fitting a line to population values, NCHS uses (at least)three different targets:
I Unweighted Slope: slope ∝∑T
t=1 Pt × yeartI Population weighted Slope: slope ∝
∑Tt=1 NtPt × yeart
I Sample variance weighted Slope: slope ∝∑T
t=1Pt×yeartvar(P̂t)
I These three estimates will all be very similar if the underlyingpopulation size does not change and if the sample size/designdoesn’t change
![Page 29: Development of Trend Analysis Guidelines at NCHS · PDF fileDevelopment of Trend Analysis Guidelines at NCHS Donald Malec Associate Director of Science O ce of Research and Methodology](https://reader030.fdocuments.net/reader030/viewer/2022032613/5a78cb407f8b9a70238c8644/html5/thumbnails/29.jpg)
Methodological Issues: What Slope to Estimate?
I Not the usual issue of how to estimate (i.e. efficiency) but,rather, what to estimate
I When fitting a line to population values, NCHS uses (at least)three different targets: ∑T
I Unweighted Slope: slope ∝ t=1 Pt × yeart
I Population weighted Slope: slope ∝∑T
t=1 NtPt × yeartI Sample variance weighted Slope: slope ∝
∑Tt=1
Pt×yeartvar(P̂t)
I These three estimates will all be very similar if the underlyingpopulation size does not change and if the sample size/designdoesn’t change
![Page 30: Development of Trend Analysis Guidelines at NCHS · PDF fileDevelopment of Trend Analysis Guidelines at NCHS Donald Malec Associate Director of Science O ce of Research and Methodology](https://reader030.fdocuments.net/reader030/viewer/2022032613/5a78cb407f8b9a70238c8644/html5/thumbnails/30.jpg)
Methodological Issues: What Slope to Estimate?
I Not the usual issue of how to estimate (i.e. efficiency) but,rather, what to estimate
I When fitting a line to population values, NCHS uses (at least)three different targets: ∑T
I Unweighted Slope: slope ∝ t=1 Pt × year∑ tT
I Population weighted Slope: slope ∝ t=1 NtPt × yeart
I Sample variance weighted Slope: slope ∝∑T
t=1Pt×yeartvar(P̂t)
I These three estimates will all be very similar if the underlyingpopulation size does not change and if the sample size/designdoesn’t change
![Page 31: Development of Trend Analysis Guidelines at NCHS · PDF fileDevelopment of Trend Analysis Guidelines at NCHS Donald Malec Associate Director of Science O ce of Research and Methodology](https://reader030.fdocuments.net/reader030/viewer/2022032613/5a78cb407f8b9a70238c8644/html5/thumbnails/31.jpg)
Methodological Issues: What Slope to Estimate?
I Not the usual issue of how to estimate (i.e. efficiency) but,rather, what to estimate
I When fitting a line to population values, NCHS uses (at least)three different targets: ∑T
I Unweighted Slope: slope ∝ Pt ×t=1 year∑ tT
I Population weighted Slope: slope ∝ t=1 NtPt × year∑ tT
I Sample variance weighted Slope: slope ∝ Pt×yeartt=1 var(P̂t)
I These three estimates will all be very similar if the underlyingpopulation size does not change and if the sample size/designdoesn’t change
![Page 32: Development of Trend Analysis Guidelines at NCHS · PDF fileDevelopment of Trend Analysis Guidelines at NCHS Donald Malec Associate Director of Science O ce of Research and Methodology](https://reader030.fdocuments.net/reader030/viewer/2022032613/5a78cb407f8b9a70238c8644/html5/thumbnails/32.jpg)
Methodological Issues: What Slope to Estimate?
I Not the usual issue of how to estimate (i.e. efficiency) but,rather, what to estimate
I When fitting a line to population values, NCHS uses (at least)three different targets: ∑T
I Unweighted Slope: slope ∝ t=1 Pt × year∑ tT
I Population weighted Slope: slope ∝ t=1 NtPt × year∑ tT
I Sample variance weighted Slope: slope ∝ Pt×yeartt=1 var(P̂t)
I These three estimates will all be very similar if the underlyingpopulation size does not change and if the sample size/designdoesn’t change
![Page 33: Development of Trend Analysis Guidelines at NCHS · PDF fileDevelopment of Trend Analysis Guidelines at NCHS Donald Malec Associate Director of Science O ce of Research and Methodology](https://reader030.fdocuments.net/reader030/viewer/2022032613/5a78cb407f8b9a70238c8644/html5/thumbnails/33.jpg)
Methodological Issues: Survey estimates may be correlatedbetween years
I Surveys estimates such as from NHIS are dependent betweenyears- Software will take into account correlation but record-leveldata is needed- Many estimation operations work from table estimates (i.e.,correlations are not typically constructed for all items)
I Incorporating correlation into prevalence estimation usuallyresults in small changes but there has been no systematicunderstanding
I Requiring analysis to always include correlation will increaseworkload, could reduce output
I Will recommend individual reports always incorporatedependencies but not clear on large pubs like HUS and HP
![Page 34: Development of Trend Analysis Guidelines at NCHS · PDF fileDevelopment of Trend Analysis Guidelines at NCHS Donald Malec Associate Director of Science O ce of Research and Methodology](https://reader030.fdocuments.net/reader030/viewer/2022032613/5a78cb407f8b9a70238c8644/html5/thumbnails/34.jpg)
l l
l
l l
l
ll
l
l
1980 1990 2000 2010
05
1015
2025
30
Year
perc
ent
I Pick time period based on a specific policy change?
I Focus interest on past decade?
I Interested in what has been happening “recently”?
I issue: is it an interesting trend or a statistical anomaly?
Methodological Issues: How to pick a time frame?
I Explaining an entire long trend may not be relevant
![Page 35: Development of Trend Analysis Guidelines at NCHS · PDF fileDevelopment of Trend Analysis Guidelines at NCHS Donald Malec Associate Director of Science O ce of Research and Methodology](https://reader030.fdocuments.net/reader030/viewer/2022032613/5a78cb407f8b9a70238c8644/html5/thumbnails/35.jpg)
l l
l
l l
l
ll
l
l
1980 1990 2000 2010
05
1015
2025
30
Year
perc
ent
I Pick time period based on a specific policy change?
I Focus interest on past decade?
I Interested in what has been happening “recently”?
I issue: is it an interesting trend or a statistical anomaly?
Methodological Issues: How to pick a time frame?
I Explaining an entire long trend may not be relevant
![Page 36: Development of Trend Analysis Guidelines at NCHS · PDF fileDevelopment of Trend Analysis Guidelines at NCHS Donald Malec Associate Director of Science O ce of Research and Methodology](https://reader030.fdocuments.net/reader030/viewer/2022032613/5a78cb407f8b9a70238c8644/html5/thumbnails/36.jpg)
l l
l
l l
l
ll
l
l
1980 1990 2000 2010
05
1015
2025
30
Year
perc
ent
I issue: is it an interesting trend or a statistical anomaly?
Methodological Issues: How to pick a time frame?
I Explaining an entire long trend may not be relevant
I Pick time period based on a specific policy change?
I Focus interest on past decade?
I Interested in what has been happening “recently”?
![Page 37: Development of Trend Analysis Guidelines at NCHS · PDF fileDevelopment of Trend Analysis Guidelines at NCHS Donald Malec Associate Director of Science O ce of Research and Methodology](https://reader030.fdocuments.net/reader030/viewer/2022032613/5a78cb407f8b9a70238c8644/html5/thumbnails/37.jpg)
l l
l
l l
l
ll
l
l
1980 1990 2000 2010
05
1015
2025
30
Year
perc
ent
Methodological Issues: How to pick a time frame?
I Explaining an entire long trend may not be relevant
I Pick time period based on a specific policy change?
I Focus interest on past decade?
I Interested in what has been happening “recently”?
I issue: is it an interesting trend or a statistical anomaly?
![Page 38: Development of Trend Analysis Guidelines at NCHS · PDF fileDevelopment of Trend Analysis Guidelines at NCHS Donald Malec Associate Director of Science O ce of Research and Methodology](https://reader030.fdocuments.net/reader030/viewer/2022032613/5a78cb407f8b9a70238c8644/html5/thumbnails/38.jpg)
0 2 4 6 8 10
0.0
0.2
0.4
0.6
0.8
1.0
year
p
l
l
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l
l
l
l
l
l
l
l
Methodological Issues: Choice of transformation?
I View choice of transformation as flexible( “ all transformations are wrong but ...”)
I Case in point: logistic regression
![Page 39: Development of Trend Analysis Guidelines at NCHS · PDF fileDevelopment of Trend Analysis Guidelines at NCHS Donald Malec Associate Director of Science O ce of Research and Methodology](https://reader030.fdocuments.net/reader030/viewer/2022032613/5a78cb407f8b9a70238c8644/html5/thumbnails/39.jpg)
Methodological Issues: Choice of model?
I View choice of model as flexible ( “ all models are wrong ...”)I For trends, NCHS seems to rely on linear splines (joinpoint)
and polynomial regressionI joinpoint software:
I selection is defensible from a design-based viewI accounts for multiple testing in model choiceI pinpoints an exact time point where a change takes place
I polynomial regression model:I useful for checking deviations from linearityI relies on off-line separate multiple comparison model fitting
I how important is it to always check the overall fit of the finaltrend model?
I trade-off between false positives and false negatives?I is the complexity of a model obvious sometimes?
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I Analysis with a small number of time points (3 or 4)I is trend analysis appropriate?
I Yes - can still evaluate linearity or lack ofI No - what does linearity mean for such a few points? - look at
pairwise differences
Methodological Issues: Other Issues
I Collapsing years togetherI individual estimates fail precision requirements for publicationI group individual estimates into reliable groups of neighboring
yearsI do a trend analysis on grouped dataI theory states: regression estimates more precise if data not
groupedI dilemma: present slope for ungrouped data with grouped
individual estimates?
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Methodological Issues: Other Issues
I Collapsing years togetherI individual estimates fail precision requirements for publicationI group individual estimates into reliable groups of neighboring
yearsI do a trend analysis on grouped dataI theory states: regression estimates more precise if data not
groupedI dilemma: present slope for ungrouped data with grouped
individual estimates?
I Analysis with a small number of time points (3 or 4)I is trend analysis appropriate?
I Yes - can still evaluate linearity or lack ofI No - what does linearity mean for such a few points? - look at
pairwise differences
![Page 42: Development of Trend Analysis Guidelines at NCHS · PDF fileDevelopment of Trend Analysis Guidelines at NCHS Donald Malec Associate Director of Science O ce of Research and Methodology](https://reader030.fdocuments.net/reader030/viewer/2022032613/5a78cb407f8b9a70238c8644/html5/thumbnails/42.jpg)
Guidance Not Planned:
I Detailed guidance on software
I Time series methods
I Age period cohort models
I Determining underlying correlates of trend
I Causal analysis
I Superpopulation models
I Model fitting - new methods
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What should guidance on trends consist of?
I What is the balance between subject matter expertise andstatistical testing?
I How to guide multiple testing for balancing betweenfalse-positive and false negative conclusions?
I How much specific guidance should be provided to anticipatechallenges to conclusions?
I How much guidance should be directed to researchers outsideof NCHS?
I How much detail should reports include regardingmethods/guidance used?