st: question about standardizing

[Rosa Gini <rosa.gini@arsanita.toscana.it>]

i have some doubts about standardizing rates in stata.

i've always used -dstdize-. in fact what this command does is 
standardizing binomial variable, doesn't it'? variance is calculated on 
lines 387-391 of the dstdize.ado file (i'm reading the file from base 
distribution of stata 9), and the formula is that of a binomially 
distributed variable.

this make it suitable for standardizing *proportions*.

i've discovered recently that in stata 9 standardization is also 
possible for means, with the -mean- command and the -stdize, and a new 
command is available for proprtions, namely the -proportion- command. if 
i understand the command -ratio- is a generalization of the previous, in 
case data are aggregated.

now the question are:

1) what if i need to standardize actual rates, i.e., poisson variables?
2) what if i have a dataset for aggregated means?  for example: i need 
to calculate the average length of stay in hospital for a given 
intervention, but i only have aggregated length of stay, for example


state  age    tot     sub
             al_los   jects
- ----------------------------
1       65    500        50
2       65    613        57
3       65    802        75
1       75    470        40
2       75    715        37
3       75    950        60


i guess that in order to compute confidence intervals i would also need 
the sums of the squares of the lengths of stay (assuming length of stay 
normally distributed), am i correct? well if i had it, would it be 
possible to use a stata command to produce standardized means with 
confidence intervals?

thanks for any suggestion!!

		rosa gini

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