Re: st: Chi-Square?

[Marcello Pagano <pagano@hsph.harvard.edu>]

Another question to ask is, how was that category chosen?  If it was 
chosen ex post as the one providing the largest difference, then you 
need to look at the distribution of the largest; a different 
distribution from the normal chi-squared distribution.  If it was chosen 
a priori and this is the only one you wish to test, then that is a 
different story.

m.p.

Maarten buis wrote:


> --- Janelle Knox <babeerage@gmail.com> wrote:
>  
>
> > I have a variable that asks whether retirement income is
> > less than expected and has five options(more, less, same, not sure,
> > etc).  Is there a way to test whether one of the options (in this
> > case-2) retirement is less than expected) is significantly higher
> > than the variable mean?  So of 2500 respondants 1700 suggest that
> > retirement is less than expected.  How do I test if this is
> > signficant?  
> >    
> Significant means that you reject the null hypothesis, so you need a
> nul hypothsesis. I read you line "Is there a way to test whether one of
> the options (in this case-2) retirement is less than expected) is
> significantly higher than the variable mean?" as meaning that your null
> hypothesis is that you think that all categories receive the same
> proportion of respondents, so each category should receive 500 cases.
> Given the large deviation of the actual value (1700) and the sample
> size   I would be very surprised if you can not reject the null
> hypothesis. That is not surprising since it is not a very reasonable
> null hypothsis, I see no reason why such likert-like items would be
> uniformly distributed. So rejecting that hypothesis is not very
> informative and you might want to think up a more meaningful
> hypothesis.  
> You can test it with a chi square test, remeber that the formula is
> sum((O-E)^2/E), O is the observed value, E is the expected value. In
> Stata you can type:
> di (1700-500)^2/500 + (800-2000)^2/2000
> which results in 3600, with in this case one degree of freedom. As
> expected this is significant for any reasonable significance level.
>
> HTH,
> Maarten
>
>
> -----------------------------------------
> Maarten L. Buis
> Department of Social Research Methodology
> Vrije Universiteit Amsterdam
> Boelelaan 1081
> 1081 HV Amsterdam
> The Netherlands
>
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>
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>
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