I have executed a Repeated Measures ANOVA with one DV (latency) and one within subject factor (acoustic condtion: 3 levels) by bootstrapping my sampling distribution of F from the empirical sample distribution. I chose to resample because the sample distribution deviates from normality a lot. The overall F is significant and now I wish to decompose this with contrasts to ask if latencies to acoustic condition #1 are different than acoustic condition #2 + #3. However, I don't know where to begin to write a program to do contrasts with a resampling technique. Any ideas would be terrific. Thanks, Alex -- Alexander T Baugh Section of Integrative Biology Univ. of Texas at Austin C0930 Austin, TX 78712 http://darktropic.blogspot.com/
Daniel Lakeland
2007-Oct-16 14:37 UTC
[R] Bootstrapping Contrasts for Repeated Measures ANOVA
On Mon, Oct 15, 2007 at 11:19:35PM -0500, Alex Baugh wrote:> However, I don't know where to begin to write a program to do > contrasts with a resampling technique.select a random sample (with replacement) from the population with factor level 1, and a random sample from the population with factor level 2. Compute the difference in averages. This is a single sample of the "difference of averages". Do this procedure several thousand times. You will have a bootstrap distribution of the difference in averages. Am I missing some other issue? -- Daniel Lakeland dlakelan at street-artists.org http://www.street-artists.org/~dlakelan
Two follow up questions from post regarding bootstrapping contrasts for a RM ANOVA: 1. Because my data are repeated measures, isn't it true that I want to shuffle my column heading individually for each subject (row) by resampling WITHOUT replacement? 2. For my DV (latency) I have 3 columns of data (3 levels) for each subject: treatment 1 treatment 2 treatment 3 Subject 1 43 sec 110 sec 65 sec Subject 2 400 sec 650 sec 430 sec Subject 3 35 sec 40 sec 50 sec . . . . . . . . . . . . . . . The data are nowhere near normally distributed, so I bootstrapped the RM ANOVA, which was signficant. Now I want to do an orthogonal contrast asking if (treatment 1) is different than (treatment 2 + treatment 3) because this is the a priori sensible question to ask given the overall effect. If this means I would average columns 2 and 3 I think this is statistically wrong due to a difference in sampling? Thanks, Alex Thanks -- Alexander T Baugh Section of Integrative Biology Univ. of Texas at Austin C0930 Austin, TX 78712 http://darktropic.blogspot.com/
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