Suggested answer to exercise: Can sutures get wet?, 2

The Results section of the paper contined the following table:

Baseline comparison of intervention (wet) and control (dry) group. Values are numbers (percentages) unless stated otherwise
Variable Wet (intervention) (n=450) Dry (control) (n=420) P value
Mean (SD) age (years) 55.9 (16.6) 56.5 (16.2) 0.58
Male patients 249 (55) 208 (50) 0.08
Mean (SD) days to removal of sutures 8.6 (2.2) 8.6 (2.2) 1
Presence of diabetes 9 (2) 14 (3) 0.2
History of other medical condition* 8 (2) 10 (2) 0.5
Treated with 1% lignocaine adrenaline 435 (97) 411 (98) 0.3
Excision of skin cancer 294 (65) 289 (69) 0.3
Excision at lower limb 112 (25) 106 (25) 1
* Chronic obstructive pulmonary disease (n=8), anaemia (1), "aspirin" (2), "steroids" (3), "warfarin" (2), ischaemic heart disease (1), and peripheral vascular disease (1).

Question 2: Is this a null hypothesis which should be tested in a randomised trial? What would it mean if one of these tests was significant?

Suggested answer 2

The subjects were randomised into two groups. This means that each treatment group is a random sample from the same population. The null hypothesis is therefore true.

We are testing a null hypothesis which we know to be true. This is a complete waste of time. If a difference is significant it must be one of the one in every 20 tests of a true null hypothesis which is significant.

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Last updated: 31 July, 2006.

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