negative values of wtsupp 1975 and before

#1

Hello –

It seems that there are negative values of wtsupp for years 1975 and before (specific details are below).

Are these mistakes? or is there something I’m not understanding?

Thanks very much,

Leah Brooks

. summ wtsupp if wtsupp < 0

Variable | Obs Mean Std. Dev. Min Max
-------------±-------------------------------------------------------
wtsupp | 497 -400.0935 727.6166 -11366.81 -1.12

. tab year if wtsupp < 0

Survey year | Freq. Percent Cum.
------------±----------------------------------
1962 | 33 6.64 6.64
1968 | 61 12.27 18.91
1969 | 79 15.90 34.81
1970 | 18 3.62 38.43
1971 | 25 5.03 43.46
1972 | 83 16.70 60.16
1973 | 78 15.69 75.86
1974 | 63 12.68 88.53
1975 | 57 11.47 100.00
------------±----------------------------------
Total | 497 100.00

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#2

The negative weights are considered valid, and are designed to account for oversampling. However, since most stats packages can not accommodate them, and since the number of affected cases is small, some researchers simply chose to exclude those cases. The existence of these negative weights is briefly mentioned in the WTSUPP comparability statement.

I hope this helps.

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