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| # | |
| # cohens-d.R, 6 Jan 16 | |
| # Data from: | |
| # | |
| # Example from: | |
| # Evidence-based Software Engineering: based on the publicly available data | |
| # Derek M. Jones | |
| # | |
| # TAG example | |
| source("ESEUR_config.r") | |
| plot_layout(1, 4) | |
| par(mar=c(5, 1, 4, 1)+0.1) | |
| pal_col=rainbow(2) | |
| norm_mean=2.5 | |
| norm_sd=1 | |
| plot_cohen=function(m_diff, sd_val) | |
| { | |
| xpoints=seq(0, norm_mean+norm_sd*2.5, by=0.01) | |
| ypoints=dnorm(xpoints, mean=norm_mean, sd=norm_sd) | |
| x2points=seq(0, norm_mean+m_diff+(norm_sd+sd_val)*2.5, by=0.01) | |
| y2points=dnorm(x2points, mean=norm_mean+m_diff, sd=norm_sd+sd_val) | |
| x_bounds=range(xpoints, x2points) | |
| max_y=max(ypoints, y2points) | |
| plot(xpoints, ypoints, type="l", col=pal_col[1], fg="grey", col.axis="grey", yaxt="n", | |
| bty="n", yaxt="n", | |
| xlim=x_bounds, ylim=c(0, max_y), | |
| xlab="", ylab="") | |
| lines(x2points, y2points, col=pal_col[2], fg="grey", col.axis="grey") | |
| # Pool the standard deviations | |
| d_val=m_diff/sqrt((norm_sd^2+(norm_sd+sd_val)^2)/2) | |
| text(norm_mean, max_y*0.2, paste0("d=", d_val), cex=1.3) | |
| } | |
| # Find the sd that produces a specified Cohen's d for a given mean difference | |
| matching_sd=function(m_diff, d_val) return(sqrt(2*(m_diff/d_val)^2-1)-1) | |
| plot_cohen(0.5, 0) | |
| plot_cohen(1.0, 0) | |
| plot_cohen(0.45, matching_sd(0.45, 0.5)) | |
| plot_cohen(1.2, matching_sd(1.2, 1.0)) | |