The default variable type for predict is float. If you specify double you will
get much higher precision.
. use "C:\Stata\auto.dta", clear
(1978 Automobile Data)
. qui reg price mpg
. predict double res, res
. sum res
Variable | Obs Mean Std. Dev. Min Max
-------------+-----------------------------------------------------
res | 74 -2.58e-13 2605.621 -3184.174 9669.721
Scott
----- Original Message -----
From: "Giovanni Vecchi" <[email protected]>
To: <[email protected]>
Sent: Saturday, November 09, 2002 3:45 AM
Subject: st: sum of residuals=zero?
> Dear statalisters:
>
> I would appreciate your comments on the following:
>
> use auto.dta
> regress price mpg
>
> (output omitted)
>
> predict resid,res
>
> egen sumres=sum(resid)
>
> sum sumres
>
> Variable | Obs Mean Std. Dev. Min Max
> -------------+-----------------------------------------------------
> sumres | 74 -.0004654 0 -.0004654 -.0004654
>
>
> The sum of residuals (which should be zero according to the theory) is
> -.0004654. This estimates looks "high" to me.
> I run the code above in Gauss and obtained a much lower estimates
> (something like 9*10^-10).
>
> Any suggestion to understand the reason for the above discrepancy?
>
>
> Thank you.
>
> Giovanni
>
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