Help needed for sample size determination

[Gpe. Virginia Nevarez]

First of all, to make any statistical considerations you should have a 
random sample from your population, in this case, you should had selected 
the serotypes of the 40 strains studied randomly.

If this is true, then besides the confidence level (95%) we need to know an 
error margin and this will depend on the type of biological caracteristics 
that you have measured (either a discrete or continuos variable).

If you can send that information, we might be able to help you finding the 
sample size.....


Vicky

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