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# Re: st: ZOIB procedure

 From Prerna S <[email protected]> To [email protected] Subject Re: st: ZOIB procedure Date Tue, 20 Sep 2011 06:19:20 -0400

```I misunderstood your previous response and so please disregard my last email.

What i really should have asked is how does the marginal effects
option in zoib combine the effects of all 2-3 equations in the model?
Heckman (I understand it's a different procedure and not really
comparable) uses a mills ratio to do so. Does zoib do something
similar?

Prerna

On 20 September 2011 06:02, Prerna S <[email protected]> wrote:
>>
>> I can think of two reasons why the statistical significance differs,
>> and they are all a variation on the point that they represent
>> different null-hypotheses: 1) The parameters represent relative
>> effects (ratios), while marginal effects represent absolute effects
>> (differences). 2) The marginal effects combine the effects on all two
>> or three equations of the model.
>>
>
> Maarten,  here is what I understand of the marginal effects. One can estimate
>
> a) mfx, predict (pr) - this is the marginal effects of the proportion
> b) mfx, predict (pr0) - marginal effects of the dependent variable = 0
> c) mfx, predict (pr1) - marginal effects of the dependent variable = 1
> d) mfx, predict (prcond) - marginal effects of the dependent variable = (0,1)
>
> I am  interested in b) and d) so I want to be clear on whether I have
> this right. So are you suggesting that of these 4 options a) is the
> best route to take whereas the remaining 3 are difficult to explain?
>
> Thanks.
> Prerna
>

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