Question on a comparison of two small groups

Extract from Statistical Questions in Evidence-based Medicine by Martin Bland and Janet Peacock.

We hope that the topic will be useful in own right, as well as giving a flavour of the book.


In a study of a possible diagnostic test for urothelial malignancies, responses obtained from cellular extracts from 8 patients with urothelial cancer and 28 controls with normal bladders were compared (Stoeber et al., 1999). A figure similar to this was presented:

Graph.  See long description indicated by d. d

+ 1. What does the graph tell us about the shapes of the distributions?
Check answer 1

+ 2. The groups were compared using an `equal variance t test'. Do you think this approach is acceptable here?
Check answer 2

+ 3. What possible approaches could be used to compare these groups?
Check answer 3

Stoeber, K., Halsall, I., Freeman, A., Swinn, R., Doble, A., Morris, L., Coleman, N., Bullock, N., Laskey, R.A., Hales, C.N., and Williams, G.H. (1999) Immunoassay for urothelial cancers that detects DNA replication protein Mcm5 in urine. Lancet 354, 1524-5.

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