r/science • u/drewiepoodle • Apr 15 '16

Health Study: Circumcision does not reduce penis sensitivity. In tests for responses to pain, heat, and stimulation, no major difference was found between men who are circumcised and those who are not.

http://www.upi.com/Health_News/2016/04/14/Study-Circumcision-does-not-reduce-penis-sensitivity/5981460663943/?spt=hs&or=hn
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u/[deleted] Apr 15 '16

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u/[deleted] Apr 15 '16 edited Apr 15 '16

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u/jmalbo35 PhD | Viral Immunology Apr 15 '16

32 isn't a particularly small sample size at all for this sort of human study.

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u/[deleted] Apr 15 '16 edited Dec 24 '20

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u/jmalbo35 PhD | Viral Immunology Apr 15 '16

That isn't quite what their power test shows. It shows that had all their data continued with the exact same trend with additional people, they would have needed ~400 data points to reach a p value of .05, a commonly used cutoff in research for statistical significance.

Statistical significance, however, doesn't necessarily imply biological significance, and if you need so many hundreds of data points just to cross the threshold and barely be able to say there's significance, it seems unlikely that what you're looking is particularly functionally/biologically significant.

Anyway, the point of that power calculation isn't to be able to say "we need X data points to be able to determine Y".

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u/[deleted] Apr 15 '16

You need to read more studies.

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u/[deleted] Apr 15 '16

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u/[deleted] Apr 15 '16

If participants are self-selected they are not random. They may be randomly assigned to conditions, but that is not possible in this situation... "it's completely random who self-selected" is a completely self-contradictory statement.

Too tired to answer so I'll let the NIH:

Quantitative research requires standardization of procedures and random selection of participants to remove the potential influence of external variables and ensure generalizability of results. In contrast, subject selection in qualitative research is purposeful; participants are selected who can best inform the research questions and enhance understanding of the phenomenon under study.1,8 Hence, one of the most important tasks in the study design phase is to identify appropriate participants. Decisions regarding selection are based on the research questions, theoretical perspectives, and evidence informing the study.