Date: Nov 2, 2005 2:08 PM
Author: Paul Velleman
Subject: [ap-stat] Re: excel for ap stat.....

At 10:44 AM -0500 11/2/05, Michael Berkley wrote:
>what do most people use for programs in their schools? we have
>data desk here, but i feel that excel is better, especially since a lot
>more people have access to it....

It won't come as much of a surprise that I think Data Desk would be a 
better choice, so let me say up front that from a teaching point of 
view, I'd also consider Minitab, JMP, or almost any statistics 
package preferable to Excel for teaching -- or for doing -- 
Statistics.

Overall, Excel is designed for accounting. It is very good at what it 
does. But it is not a database, a word processing program, or a 
statistics program, although it has some of the functions of each of 
these. If you don't use Excel for your word processing, you shouldn't 
use it for Statistics, and for much the same reasons; it isn't 
designed for that and has capabilities in those areas only to support 
its main function.

Excel's statistics have been criticized in print in a number of 
places. They use numerically unstable formulas for several things 
(variance, regression, and others), although frankly, that's unlikely 
to make much difference in AP Stat classes. But we should not 
encourage our students to use it for analyses they may actually care 
about because there is a risk of getting wrong results.

Pedagogically, Excels graphics are not suitable for Statistics. Excel 
can't make a proper histogram without much work to fool its bar chart 
program. Scatterplots show the origin by default, so they must almost 
always be re-scaled to be useful. Excel doesn't do boxplots at all. 
And the plots labeled normal probability plots are something entirely 
different (and essentially worthless). In short, the diagnostic 
graphics our students need are either missing, wrong, or hard to use. 
In my opinion, that disqualifies Excel for teaching statistics. The 
greatest advantage of using a computer for statistical analysis is 
not the convenience of the calculation but the ready availability of 
suitable displays.

Finally, the help provided with the data analysis add-in exhibits 
many of the errors that we (and AP graders) would mark as wrong. 
Those errors may help us to understand the weak background knowledge 
of the (now defunct) consulting firm that wrote the data analysis 
add-in, but they aren't something you'll want your students relying 
on.

Excel is a common place to record and keep data. And there are 
add-ins from other places (including DD/XL. which uses the Data Desk 
engine) that replace Microsoft's statistics with more competent 
versions. But then you aren't really using Excel anyway.

-- Paul

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