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***ASSOCIATION BETWEEN VARIABLES MEASURED AT THE INTERVAL-RATIO LEVEL (chapter 13)
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***Opening commands
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***Clear memory
clear all

***Start saving results window
log using "C:\course\progs\Stata13.log", replace text // Windows
log using "/course/progs/Stata13.log", replace text // Macintosh

***Open 2016 GSS
use "C:\course\data\GSS2016.dta", clear // Windows
use "/course/data/GSS2016.dta", clear // Macintosh

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***Complex survey design
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svyset [weight=wtssall], strata(vstrat) psu(vpsu) singleunit(scaled)

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***Respondent's income and education
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***Scatterplot without regression line
twoway scatter conrinc educ

***Scatterplot with regression line
twoway scatter conrinc educ || lfit conrinc educ, ytitle(Respondent's income) xtitle(Years of schooling)
twoway (scatter conrinc educ) (lfit conrinc educ), ytitle(Respondent's income) xtitle(Years of schooling) // same as above

***Regression coefficients
***Least-squares regression model
***They can be reported in the footnote of the scatterplot
svy: reg conrinc educ

***Pearson's r correlation
corr conrinc educ [aweight=wtssall]
pwcorr conrinc educ [aweight=wtssall] // same as above
pwcorr conrinc educ [aweight=wtssall], sig // Pearson's r with test of significance

***Coefficient of determination (r-squared)
di .3387^2

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***Correlation matrix
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***Respondent's income income, age, education
pwcorr conrinc age educ [aweight=wtssall], sig

***Coefficient of determination (r-squared)
***Respondent's income and age
di .1852^2

***Coefficient of determination (r-squared)
***Respondent's income and education
di .3387^2

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***CLOSING COMMANDS
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***Save data
save "Stata13.dta", replace

***Save log
log close