Tuesday, June 12, 2007

Reading Tukey's Exploratory Data Analysis:

If we want to see what our plots ought to tell us, there is no substitute for the use of tracing paper (or acetate). If we slip a well-printed sheet of graph paper just below the top sheet of a pad of tracing paper, we can plot on the top sheet of tracing paper almost as easily as if it were itself ruled. Then, when we have the points plotted, some boundary or reference lines drawn, and a few scale points ticked, we can take away the graph sheet and look at the points undisturbed by a grid. We often gain noticeably in insight by doing this. (And we have had to pay for a sheet of tracing paper rather than for a sheet of graph paper.) [...]

An alternative that:
  • can be even mre effective,

  • is no more expensive,

  • takes a little more trouble to prepare for,

replaces the tracing paper by the thin sheets of transparent plastic (acetate) made for use in overhead projectors. Two cautions are important:
  1. You can only use markers specially made for the purpose. [...]

  2. It is important to keep one's fingers off the plastic until the picture is completed. (A piece of thin graph paper, placed upside down, works very well as a hand shield.)

Much of this classic textbook is obsolete tips and tricks -- e.g. for collecting data on paper and checking that you've copied it accurately to another piece of paper. The notes on cost of tracing paper vs. graph paper vs. acetate strikes me as quite funny now!

I think I learned to graph by hand in school but never had to except as an academic exercise -- I was using graphing software before entering University (summer job in a water testing lab). I wonder what kids today do in school, if they even bother with the academic exercise. I hope so, because it was kind of fun playing with numbers on paper. For some values of fun :)

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