Jul 16

The pearls of AP Statistics 6

Do you get what you pay for? Minitab is overpriced.

They say: A pie chart is a circle having a “slice of the pie” for each category. The size of a slice corresponds to the percentage of observations in the category. A bar graph displays a vertical bar for each category. The height of the bar is the percentage of observations in the category. Typically, the vertical bars for each category are apart, not side by side (Agresti and Franklin, p.29)

I say: Firstly, about the level. When I read this, I am wondering: is AP Statistics for elementary school students? Secondly, the details of different graph types depend on the software. Excel alone has ten different chart types, with several subtypes in each. More advanced packages, such as Matlab, have even more possibilities. Drop such unimportant details, and the volume of the book will fall by one third. Thirdly, whether the vertical bars for each category are apart or side by side depends on what measures percentages, and this fact is not explained.

If the heights of bars mean percentages, then it doesn't matter if they are apart or shoulder to shoulder (but The College Board exams insist that it does). However, if the areas of bars mean percentages, then they should be shoulder to shoulder.

Finally, and most importantly, why most AP Statistics books insist on the above definitions of the pie and bar charts? It's because they recommend using Minitab. And probably they do that because Minitab pays the authors a certain percentage of the sales. Who is willing to shell out  $1,474.32 for the software plus over $200 for the book to take just one course? To me this sounds like extortion. For simpler tasks you can use Excel, which you probably have, and for advanced research you can use a free package called R.

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