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Re: st: Stanard Error for Difference in Difference cross-tabulation

 From Richard Palmer-Jones To statalist@hsphsun2.harvard.edu Subject Re: st: Stanard Error for Difference in Difference cross-tabulation Date Thu, 12 Feb 2009 11:27:30 +0000

```Thanks for the replies, and sorry not to have been clearer and the
delay in responding (student strike!)

the variables are:
label yearsedn  "years of education" // cross section in 1999
gen old = born >= 1956 & born <= 1961
gen young = born >- 1970 & born <= 1975
gen highintensity =  state >= 5 & state <=  19 // states 1 -4 = low intensity
label highintensity  "high primary school funding in 1976-81" // (i.e. treated)
gen young_high  = highintensity * young

* Maarten suggests
. reg yearsedn young highintensity young_high if young | old

Source |       SS       df       MS              Number of obs =    2698
-------------+------------------------------           F(  3,  2694) =  115.81
Model |  8584.36711     3   2861.4557           Prob > F      =  0.0000
Residual |  66562.2808  2694  24.7076024           R-squared     =  0.1142
-------------+------------------------------           Adj R-squared =  0.1132
Total |  75146.6479  2697  27.8630508           Root MSE      =  4.9707

------------------------------------------------------------------------------
yearsedn |      Coef.   Std. Err.      t    P>|t|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
young |   2.286417   .4506203     5.07   0.000      1.40282    3.170013
highintens~y |  -3.533677   .3945928    -8.96   0.000    -4.307412   -2.759941
young_high |   .7222411    .503475     1.43   0.152    -.2649952    1.709477
_cons |   6.118812   .3497354    17.50   0.000     5.433035    6.804589
------------------------------------------------------------------------------

I want a table with mean and standard errors of years of education
where the Xs are in the following table, and the marginal differences

young
0                1             difference
_______________________________________
lo             |       X         |          X      |       X
high          |       X        |          X      |        X
_______________________________________
difference  |       X         |        X         |     X

The row and column Xs can be filled in from calcuations of means (e.g
in ttest), except for the bottom right X

Maarten's suggestion is that the appropriate se is 0.503

Thanks for further help

RIchard

On Tue, Feb 10, 2009 at 5:18 PM, Steven Samuels
<sjhsamuels@earthlink.net> wrote:
> While I agree with  Maarten about the analysis procedure, I am unclear about
> the design- does "one of which" in your description refer  to region or to
>  cohort?  Was there a treated cohort and a non-treated cohort within each
> region? Or, were there two cohorts within each region, but with treatment
> differing between region?  Do you have a before/after differences , or are
> all comparisons cross-sectional?
>
> Please lay out in more detail the design of the study
>
> -Steve
>
>>
>> --- On Tue, 10/2/09, Richard Palmer-Jones wrote:
>>>
>>> I want to calculate the standard error of the mean
>>> "diffference in difference". I have samples from two
>>> cohorts in each of two regions, one of which received
>>> a treatment, and their respective years of education;
>>> how to I calculate the standard error of the
>>> difference in difference of the years of education?
>>
>> Looks to me like an interaction effect:
>> The dummy for cohort tells you how much the average
>> education differs over cohorts, and you think that
>> this difference differs across regions, so the
>> interaction effect between cohort and region gives
>> you this difference in difference, and -regress- will
>> automatically give you the standard error.
>
> *
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```

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