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# Re: st: Test for statistical significance

 From Austin Nichols To statalist@hsphsun2.harvard.edu Subject Re: st: Test for statistical significance Date Tue, 31 Aug 2010 10:50:24 -0400

```Cornelius Nattey <cornelius.nattey@nioh.nhls.ac.za>:

Regress manganese blood levels on a dummy for month equal to November,
clustering by person (or higher level if using clustered survey data,
or if there is other clustering suspected).  You might want to use
levels must be nonnegative, especially if they exhibit right skew.
The easy interpretation in the latter regression would be in terms of
a percentage difference, rather than a difference in levels.

webuse nhanes2, clear
egen c=group(strata psu)
ren female nov
qui reg zinc nov [pw=finalwgt], cl(c)
loc d=cond(sign(_b[nov])==1,"higher","lower")
di "`: var lab zinc' is " abs(_b[nov]) " `d' in November"
qui glm zinc nov [pw=finalwgt], link(log) cl(c)
di "`: var lab zinc' is " abs(exp(_b[nov])-1) "% `d' in November"
nlcom exp(_b[nov])-1

On Tue, Aug 31, 2010 at 10:24 AM, Cornelius Nattey
<cornelius.nattey@nioh.nhls.ac.za> wrote:
> Dear All,
> I have two datasets of manganese blood levels taken in August and
> November 2005. They were from the same community but mainly different
> people in the community. There may have been some repeats but I do not
> know how many if there were any. I have treated them as independent and
> not paired tests.
>
> What test should be applied to see if there is a statistically sig
> difference? Is there a difference?
>
> Thanks very much
> Cornelius
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```