st: trying to understand collapse and weights

[Nirina F <fstata@gmail.com>]

Hi,
I am using panel data over countries year.
Each country has various income variable but I wanted to use that as weights.

collapse $xvar [iw=income] , by(year)
The results I get make sense but I wanted to understand what is the
logic behind this command with [iw]
So I tried to test Stat and used the weights with collapse (sum) and I
got huge numbers for my xvars
 collapse (sum)  $xvar [iw=income] , by(year).
I would like to make sure that the following command is doing the
right weighting which is country1 has 30% of the income in the sample
in a particular year for example.

collapse $xvar [iw=income] , by(year)

Should I have created a share of income for each particular year and
country before collapsing.
Thanks,
Nina
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