Chapter 8: Analysing matched or paired data using STATA

Figure 8.1 Output for a paired t test

Figure 8.1 Descritpive statistics for paired t-test

Figure 8.1 Code

Code for figure

use "C:\Projects\Books\Presenting\data\stataData\cotinine.dta", clear
ttest cotearly = cotlate

Figure 8.2 Histogram of skewed paired data (a) before and (b) after log transformation with normal distribution curve

Figure 8.2 Code

Code for figure

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use "C:\Projects\Books\Presenting\data\stataData\cotinine.dta", clear

 **create histogram for change in blood caffeine then for change in log caffeine
 
histogram cafdiff, width(1) start(-10) frequency normal ylabel(0(50)150) ///
	xtitle(Change in blood caffeine level (ng/ml)) xlabel(-10(5)15) title(, size(small) span)
 
graph save Graph "C:\blah\fig 8.2a.gph"
 
histogram logcafdiff, width(.5) start(-7) frequency normal ylabel(0(50)150) ///
	xtitle(Change in log blood caffeine level) xlabel(-5(5)10) title(, size(small) span)
 
graph save Graph "C:\blah\fig 8.2b.gph"

**combine 2  histograms into one graph

graph combine "C:\blah\fig 8.2a.gph" "C:\blah\fig 8.2b.gph", ///
	title(Histograms of change in caffeine before and after log transformation, size(medium) span) ///
	subtitle(with Normal distribution curves (n=801))

Figure 8.3 and Box 8.5 Paired t test with back- transformation

Box 8.5 Presenting the results of a paired t test on log-transformed data

Figure 8.3 and Box 8.5 Code

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use "C:\Projects\Books\Presenting\data\stataData\cotinine.dta", clear
ttest lcafearly = lcaflate

Figure 8.4 to Box 8.7 Presenting the findings of the Wilcoxon test for matched pairs

Figure 8.4 Presenting the findings of the Wilcoxon test for matched pairs

Figure 8.4 to Box 8.7 Code

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use "C:\Projects\Books\Presenting\data\stataData\sleep.dta", clear
gen diffawakening = proneawakenings - supineawakenings
signtest diffawakening = 0

Figure 8.5 Output for a matched case-control analysis

Figure 8.5 Code

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use "C:\Projects\Books\Presenting\data\stataData\casecontrol.dta", clear
mcc case control

Box 8.10 Presenting the results of matched case- control analysis

Box 8.10 Presening results of a matched case-control analysis

Box 8.10 Code

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use "C:\Projects\Books\Presenting\data\stataData\casecontrol.dta", clear
** use casecontrol for 1st analysis as in fig 8.5

mcc case control

** now use Stata immediate command 

mcci 411 69 45 7

Figure 8.6 Output for McNemar’s test with ratio of paired proportions

Figure 8.6 Code

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use "C:\Projects\Books\Presenting\data\stataData\cotinine.dta", clear

tabulate nausea1 nausea2

mcc nausea1 nausea2