Viewing By Month : December 2004 / Main
December 17, 2004
New presentations to learn how Prism works
Until now, the only way to learn about Prism was to read our examples, find a friend to show you, or plunge in and try it. Now there is any easier way. Sit back, and watch & listen to one of our short our short animated presentations.

Posted At : 4:36 PM. | Link
December 16, 2004
Bug in post tests after repeated measures two-way ANOVA
We discovered a serious bug in how GraphPad Prism 3 and 4 (up to 4.02 and 4.0b) compute the post tests following repeated measures ANOVA.

The bug only occurs when you have arranged the data so that each row represents a different time point ard related (repeated measures) values are stacked into subcolumns. The post test calculations are correct when each column represents a different time point.

Depending on your data, the effect of the bug can vary. In many cases, the effect of the bug won't be noticeable. In other cases, the analysis mistakenly has too much power and finds 'significant' differences when it shouldn't. In other cases, the bug results in too little power and doesn't find 'significant' differences when it should.

We'll fix this bug in Prism 4.03 and 4.0c. Let me know if you want to beta test. We expect to release these versions early in the year.

It is easy to work around the bug. Learn more about the bug and how to work around it.

Posted At : 4:53 PM. | Link
Once you paste a Prism graph into Word, how do you drag it around?
There are two different ways to place a picture or object within Word. One lets you drag the picture around with the mouse, the other does not (but has other advantages). Learn about the distinction.

Posted At : 1:24 PM. | Link
December 14, 2004
Fisher's test or chi-square? Or Bernard's test?
Analyzing a two by two contingency table (comparing two proportions) seems so simple. Yet statisticians are still arguing. Fisher's test is 'exact', but some think it gives an exact answer to the wrong question (a 'Type 0' error), so also gives an approximate answer to the question you really want the answer to. More.

Posted At : 2:47 PM. | Link
December 8, 2004
Converting graphs to monochrome within Word
Many people make their Prism graphs in color, but want them in monochrome once they copy and paste them into Word. One solution is to duplicate the graph in Prism, and then change one copy to monochrome. But there is a much better way, using a feature within Word that lets you convert a graphic to monochrome or grayscale. Read more.

Posted At : 9:24 AM. | Link