exclude the data

[max tailler]

Hello,
How can I exclude firms for which I can't compute the lagged ratios?
i mean ratios (cash flow to capital ratio) CFit-1 / Kit-2 .
i dont know how can i convert that (can't compute) into stata.

[max tailler]

this is a backfilling bias

[Nick Cox]

I don't follow #1 or #2. But if a result variable is missing in certain observations, those observations will generally be ignored by other commands.

[max tailler]

There is a missing value when I run the codes. But this is right
i can't compute the ratios if the denominator is equal to zero, how can I drop the ratios?

[Nick Cox]

See #3 again. You should only drop observations with missing values on one variable if you are certain that you won't need those observations again.

Otherwise

drop if missing(foo)

will drop observations with missing values on foo, which will result if foo is a ratio and the numerator or denominator is missing or the denominator is zero.

[max tailler]

Ah, ok thank you