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Example of the quantitative version of w:Simpson's paradox.

The graphic was created by User:Schutz for Wikipedia on 14 June 2007, using the R statistical project. The program that generated and exported the graphic is given below; the uploaded version was generated slightly differently to workaround a bug during the PS to SVG conversion with pstoedit command. The layout was slightly modified using Inkscape before upload.

 
  x1 <- c(1,2,3,4)
  y1 <- x1 + 5
  
  x2 <- x1 + 7
  y2 <- x2 - 7
  
  x <- c(x1,x2)
  y <- c(y1,y2)
  
  postscript("simpson.eps", paper="special", width=4.5, height=3)
  
  par(las=1)
  par(mar=c(3,3,0.5,0.5))
  par(mgp=c(2,1,0))
  
  plot(x,y, cex=2, pch=21,
       col=rep(c("blue", "red"), each=4), bg=rep(c("lightblue", "pink"), each=4),
       xlim=range(x)+c(-2,2), ylim=range(y)+c(-2,2))
  abline(lm(y1 ~ x1), col="blue", lwd=2)
  abline(lm(y2 ~ x2), col="red", lwd=2)
  abline(lm(y  ~ x), lwd=2, lty=2)
  
  dev.off()
  

 

This W3C-unspecified chart was created with R.

This work has been released into the public domain by its author, Schutz. This applies worldwide. In some countries this may not be legally possible; if so: Schutz grants anyone the right to use this work for any purpose, without any conditions, unless such conditions are required by law.

 

This W3C-unspecified chart was created with R.