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estimation of median conditional with apollo_conditionals()

Ask questions about post-estimation functions (e.g. prediction, conditionals, etc) or other processing of results.
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valeria toledo
Posts: 10
Joined: 20 Aug 2020, 15:20

estimation of median conditional with apollo_conditionals()

Post by valeria toledo » 07 May 2021, 11:12

Hi I am using a MXL model with lognormal cost.
I would like to be able to extract the median of the lognormal distribution of the cost parameter.
Is it possible to change the source code or add something into the function "apollo_conditionals()" so that it provides the conditional median (and sd) of the lognormal distribution, rather than the mean?

Kind regards

dpalma
Posts: 125
Joined: 24 Apr 2020, 17:54

Re: estimation of median conditional with apollo_conditionals()

Post by dpalma » 10 May 2021, 15:26

Hi Valeria,

No, sadly apollo_conditionals does not allow you to get the median of the posterior for each individual. However, you may be able to calculate it from the mean and s.d. reported by Apollo.

The mean of a lognormal is: e^( m + (s^2)/2)
and the s.d. is: sqrt( (e^(s^2) - 1)*e^(2*m + s^2) )

Where m and s are the underlying normal's mean and standard deviation. You know the value of the mean and the s.d. of the lognormal, so you may be able to calculate m and s (I haven't tried). Once you have the values of m and s, you can easily calculate the median as e^m. You would have to repeat this calculation for each individual.

Cheers
David

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