ISC and Wilcoxon signed rank test [Nonparametrics]

posted by d_labes  – Berlin, Germany, 2017-01-04 11:21 (2723 d 00:42 ago) – Posting: # 16927
Views: 10,344

Dear mittyri,

❝ Could you please enlighten my pea-sized brain:


❝ ❝ Method 1:

❝ ❝ Calculate the differences T-R for each subject and do a Wilcoxon signed rank test with these intra-subject differences

❝ For each subject we got one difference (contrast). How to perform the test using only one value for each subject?


:confused: Don't get your point.

May be you are confused by my writing

❝ ❝ Calculate the differences T-R for each subject


Sorry. But I'm not an English man (but only "een Balina, wa"). One difference for each subject, calculated as above described and analyzed by a Wilcoxon signed rank test (non-parametric analogue of a paired t-test) using of course the intra-subject contrasts of all subjects under study.

Let's take a hypothetical example, 8 subjects, ISC already calculated:
subj <- c(1,   2,    3,    4,   5,   6,     7,    8)
isc  <- c(0, 0.5, -0.5, 0.25, 0.0, 1.0, -0.25, -1.0)
tr <- wilcox.test(isc, conf.int = T, conf.level = 0.9, exact=F)

tr$estimate is the point estimate of T-R, tr$conf.int its 90% confidence interval.

exact=F is to avoid warnings
cannot compute exact p-value with ties
cannot compute exact p-value with zeroes


If you are interested in an exact solution wich can handle ties and zero's see package exactRankTests or coin.

Regards,

Detlew

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