I got some selected cases from the OCC1990 in the years '60, '70 and '80, but every case’s PERWT has same value, 20. I’m not sure how to interpret this mean. Although I can’t believe that well, does the PERWT value of 20 mean that the case represents 20 people with the same characteristics?

I’m sorry to ask basic question.

Thank you for your help.

You are observing uniform values of PERWT because the samples you’ve selected are “flat” samples. This means that every observation within the sample represents the same number of people in the total population.

In the 1960 5% sample and the 1980 5% state sample, 1 person in the sample represents 20 people in the population. However, in 1970 1 person in the sample represents 100 people in the population, therefore for your 1970 sample(s) you should see a uniform PERWT of 100. Here is some information about each sample.