Re: st: mean and SD by categories

[Federico Belotti <f.belotti@gmail.com>]

This could be a strategy to get a table using Ben Jann -estout- command

qui {
forval a=1/2 {
	forval b=1/7 {
		forval c=1/5  { 
			sum bmi if sex==`a' & agegp==`b' & ses==`c'
			mat mean = nullmat(mean) \ r(mean)
			mat sd = nullmat(sd) \ r(sd)
			mat up = nullmat(up) \ r(mean)+(1.96*r(sd)/r(N))
			mat lo = nullmat(lo) \ r(mean)-(1.96*r(sd)/r(N))
			local lab `"`lab' "sex=`a' agegp=`b' ses=`c'""'
		}
	}
}
mat all = (mean,sd,lo,up)
mat rown all = `lab'
mat coln all = mean sd lb ub
noi estout m(all), varw(22) mlab(,none)
}

Federico

On Jul 16, 2013, at 2:23 PM, Nick Cox wrote:

> There are various problems with your approach.
> 
> 1. The immediate problem is that you cycle over combinations of
> categories creating local macros with names like mean111, sd111, and
> so forth.
> 
> But a command like
> 
> display mean111
> 
> is understood by Stata to mean that you want to see a value of a
> variable -mean111- or a scalar -mean111-, but you have no such
> variable or scalar, hence the message you received.
> 
> To see the value of a local macro, you would need to do something like
> 
> display `mean111'
> 
> 2. Adding +/- 1.96 SD to the mean is an attempt to get 95% confidence
> intervals. But there are at least two problems here. 1.96 is an
> optimistic multiplier and a more accurate multiplier would be based on
> the t-distribution. However, that's secondary compared with using SDs
> when you should be using standard errors.
> 
> 3. A strategic difficulty here is that creating lots of local macros
> first is not a good way to create graphs. In fact if you are a novice
> in programming trying to program graphs from scratch is not advisable.
> In your case 70 cross-combinations seems likely to produce only a very
> complicated graph. Much depends on whether each cross-combination is
> well enough represented to show stable patterns.
> 
> -stripplot- from SSC may be of help. It has a -ci- option that means
> that confidence intervals are shown for you.
> 
> Nick
> njcoxstata@gmail.com
> 
> 
> On 16 July 2013 12:43, Dherani, Mukesh <M.K.Dherani@liverpool.ac.uk> wrote:
>> Dear all,
>> I am very novice in programming.
>> I have a dataset with BMI by three categorical variables age (7 groups), sex (2 groups) and SES (5 groups).  I was to generate a line graph showing mean BMI with 95%CI by age , sex  and SES.  Below is my code to create local that I want to use in twoway line graph:
>> 
>> forval a=1/2 {
>> forval b=1/7 {
>> forval c=1/5  {
>> sum bmi if sex==`a' & agegp==`b' & ses==`c'
>> local mean`a'`b'`c'=r(mean)
>> local sd`a'`b'`c'=r(sd)
>> local up`a'`b'`c'=r(mean)+(1.96*r(sd))
>> local lo`a'`b'`c'=r(mean)-(1.96*r(sd))
>> di mean`a'`b'`c' sd`a'`b'`c' up`a'`b'`c' lo`a'`b'`c'
>> }
>> }
>> }
>> 
>> 
>> At the end of this command stata says mean111 was not found!
>> Secondly, I want graph to show me mean bmi (y axis) and age (x axis) for each ses for each sex separately. Should I carry this out in the loop or outside the loop?
>> 
>> Any help is highly appreciated.
>> 
>> BW,m
>> 
>> 
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-- 
Federico Belotti, PhD
Research Fellow
Centre for Economics and International Studies
University of Rome Tor Vergata
tel/fax: +39 06 7259 5627
e-mail: federico.belotti@uniroma2.it
web: http://www.econometrics.it


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