This is a question from Wooldridge textbook.

  1. Using just the years 1990 and 1993, estimate the equation from part (i) by pooled OLS. Ignore the serial correlation problem in the composite errors. Do you find any evidence for a deterrent effect?
The year variable has 87, 90 and 93. If I use the code:
Code:
reg mrdrte d93 exec unem if year==90 | 93
, which is incorrect.

The correct code (at least shows the correct regression estimate) is:
Code:
reg mrdrte d93 exec unem if inrange(year,90,93)
Can anyone tell me why the first code is wrong? Is the second code very good?

Many thanks in advance!