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st:re:re: if-sentences in Stata

From   Kit Baum <>
Subject   st:re:re: if-sentences in Stata
Date   Fri, 28 Nov 2008 10:54:32 -0500

Linn said

1) When you type L.flow is that referring to the
Value in cell [_n-1]?

2) you type flow = (shift == - 1)*..... and then + (shift == 1)*...
Adding the + there and then (shift == 1) means Stata should
execute the last command only if the (shift == 1) is true?

The 2/1 at last means starting in cell 2 and continue in
Steps of 1, right? As you probably understand I am
Kind of new to programming syntax in Stata.

(1) yes.

(2) I diagrammed the logic of your original program, which did different things depending on whether shift was -1 or +1, and then depending on the subsidiary expression involving last period's flow. The construct

(foo == 1) * ( AAA) + (foo = 2) * (BBB) will either execute the AAA code or the BBB code, presuming that every observation has foo equal to either 1 or 2.

(3) Yes, the numlist 2/l (that is 2/L) means from observation 2 to the Last. You must start at 2 to avoid L.flow being missing in period 1, which would propagate missings through the sequence.

Kit Baum, Boston College Economics and DIW Berlin
An Introduction to Modern Econometrics Using Stata:

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