st: Re: impute vs. predict

["Rodrigo A. Alfaro" <raalfaroa@gmail.com>]

The answer is clear in the manual: -impute- uses the best 
available set to make the prediction. For example 
impute y x1 x2, g(z1)
reg y x1 x2
predict z2
reg y x1
predict z3
reg y x2
predict z4

then z1 will be 
- y if y is not missing
- z2 if y is missing, but x1 and x2 are not 
- z3 if y and x2 are missing
- z4 if y and x1 are missing
- missing if y, x1 and x2 are missing.

Rodrigo.


----- Original Message ----- 
From: "Caleb Southworth" <caleb@uoregon.edu>
To: <statalist@hsphsun2.harvard.edu>
Sent: Thursday, March 01, 2007 3:50 PM
Subject: st: impute vs. predict



> What is the difference between -impute- and -reg- followed by
> -predict-?
>
> For example:
>
> . impute t_aflcio_mem temp year if inrange(year,1956,2005),
> g(i_aflcio_mem)
> 44.00% (22) observations imputed
>
> . quietly reg t_aflcio_mem temp year if inrange(year,1956,2005)
>
> . predict yhat if inrange(year,1956,2005)
> (option xb assumed; fitted values)
> (77 missing values generated)
>
> . list year i_aflcio_mem yhat in 77/87
>
>     +----------------------------+
>     | year   i_aflc~m       yhat |
>     |----------------------------|
> 77. | 1956    15707.5   14748.04 |
> 78. | 1957    15965.1   15062.62 |
> 79. | 1958    13849.3    14816.2 |
> 80. | 1959    13701.4   14569.78 |
> 81. | 1960    13866.6   14336.76 |
>     |----------------------------|
> 82. | 1961    13618.2   14103.74 |
> 83. | 1962    13784.8   14021.69 |
> 84. | 1963    13904.2   13939.65 |
> 85. | 1964    14235.3   14286.39 |
> 86. | 1965    14815.9   14633.13 |
>     |----------------------------|
> 87. | 1966    15372.1   15372.03 |
>
> . pwcorr yhat i_aflcio_mem
>
>             |     yhat i_aflc~m
> -------------+------------------
>        yhat |   1.0000
> i_aflcio_mem |   0.8947   1.0000
>
> OK, so the reg prediction and imputation differ, but why? -eret li-
> indicates that -impute- is -regress-.
>
> Thanks!
>
> Caleb
> caleb@uoregon.edu
> University of Oregon Sociology
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