[Tutor] FYI: An Introduction to Interactive Programming in Python

[Prasad, Ramit]

Alan Gauld wrote:
> 
> On 09/04/13 13:47, Steven D'Aprano wrote:
> 
> >> Since when did 30 become a representative sample size?
> >
> > If they are randomly selected, 30 is likely plenty for a representative
> > sample size. In surveys, a sample size of 30 gives you a margin of error
> > of about 15%, which isn't too bad.
> 
> Hmm, if I'd gone to my manager (and especially the finance director)
> with a project proposal based on assumptions with a 15% margin they'd
> have thrown me out. And if I told them I'd developed 5 key assumptions
> based on that same proposal I'd probably have been fired! I'd be looking
> for something like 300+ samples for a project like this to claim that my
> 5 key principles were valid. And its not like there is a shortage of
> computer scientists to ask (although admittedly harder to find ones with
> no formal computer training)!

Well, 15% error margin is from statistics and provable, but the layman
usually hears "30 people" and thinks "that's far too small". I certainly
did it too. :) 

Error margins are one of those surprising things like the Birthday 
Problem (at least to me). Seems like it should not be true but it is.
http://en.wikipedia.org/wiki/Birthday_problem

Honestly, with surveys the method of the survey itself makes a 
difference. This includes things like question wording, question
order, and even survey format (free form, multiple choice, etc).

Much like scientific studies, I am more interested in *how* it
was done than in some summarized (frequently sensationalized)
"findings". In my opinion, a flawed methodology is more 
frequently a problem than a small sample size. 

> 
> > 1) it is likely to be a biased selection
> 
> My suspicion is they just asked around their local department!
> But maybe I'm just overly suspicious... 

Overly suspicious or concerned based on experience? :)


~Ramit


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