I ran a variety of economic experiments in Burkina Faso in 2013, and I wanted to show how the distribution of choices changed (or did not) from the first round of the experiments to the second round of the experiments. I thought an overlapping histogram would be a simple and easy way to show this. I first coded in in Stata, which is quite easy to do.

(I use locals for all the labels etc because I do the graphs in both English and French)

twoway histogram contribpub_mai13, barwidth(50) discrete color(gs4) percent ///

histogram contribpub_aout13 , barwidth(35) discrete color(gs10) percent ///

legend(off) xtitle(“`labx3′”) ytitle(“`labx4′”) ///

subtitle(“`labx6′ = `labx9′, `labx7′ = `labx8′”, si(small)) ///

title(“`labx53′” “`labx55′”) name(comin1, replace)

graph export “$JTLjeuxoutfld\contribpub2013.png”, replace

I then tried to do the same chart in R, and this is considerably harder because I don’t know how to get the two sets of bars aligned. Finally I used “space” and set the distance between the bars on the second graph by trial and error. Turned out pretty well. But if I change the width of the second set of bars, then I have to trail and error again for all the spaces between them. I’m sure there is a mathematical formula I could write that would take any width and spread the bars out evenly… next task for me someday.

Here is the R chart and code.

contribmai.freq=table(kevanejtl$contribpub_mai13)

cbind(contribmai.freq)

contribaout.freq=table(kevanejtl$contribpub_aout13)

cbind(contribaout.freq)

### create some plots

barplot(contribmai.freq, col = “gray”, border =”black”, ylim=c(0,160) )

barplot(contribaout.freq, col = “white”, border =”black”,

add =TRUE, width=.8, space=(c(.37, .5, .5, .5, .5, .5)),

names.arg = c(“”),

ylab=(“Number of people choosing amount”), xlab=(“Amount in FCFA”),

main=(“Contributions in public goods game”))

mtext(“May 2013 = gray, August 2013 = white”)

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## About mkevane

Economist at Santa Clara University and Director of Friends of African Village Libraries.