Tuesday, January 8, 2008

Lecture 1 - additional notes and research

I was surprised to find the following statement in the Quartile entry on Wikipedia (which Prof Selcuk confirmed): "There is no universal agreement on choosing the quartile values." There is a reference to an article in American Statistician by a couple Australian professors (Hyndman and Fan). (Abstract: http://www-personal.buseco.monash.edu.au/~hyndman/papers/quantile.htm)

I was able to retrieve this article from the JSTOR Arts and Sciences 2 database via the NEIU library.

I found an interesting write-up on Defining Quartiles at Ask Dr. Math. After showing why quartiles are simple in concept but complex in execution, Dr. Math describes 5 methods for defining quartiles: Tukey, M&M, M&S, Minitab and Excel.

After reading the Dr. Math article, I see that the algorithm for defining quartiles that we discussed in class is the Minitab method, using x*(n+1)/4 to find quartile position and linear interpolation of closest data points to handle non-integral positions.

MS Excel
I was also surprised to find out that the accuracy of MS Excel is in question and that McCullough and Wilson have been writing in Computational Statistics & Data Analysis on the issues with Excel's algorithms and how they have changed in subsequent versions of MS Excel since 97.

Web Resources
I found a nice site that covers some of the material from lecture 1 (measures of central tendency and measures of spread) and more. It's called Stats4Students. I'm going to create a links section in the sidebar and add it.

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