constrained interpolation

[Nariman Sayed]

Hello everyone,

I am trying to interpolate education enrollment variable in panel data using the following code:

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ipolate edu time, gen (edul ) epolate by(country)

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However, I got negative values, while this variable can not take negative values economically. So, how can I add constrain to the range of the interpolated values.


thanks in advance !

[Joseph Coveney]

From the help file:

epolate specifies that values be both interpolated and extrapolated. Interpolation only is the default.

So, maybe

ipolate edu time, generate(edul) /* epolate */ by(country)

[Nick Cox]

Extending Joseph Coveney's suggestions, choices include

1. Don't do that, then.

2. Replace negative values with zeros.

3. Extrapolate on a scale that reflects growth patterns: interpolate on logarithms or logits, invert the transformation.

[Nariman Sayed]

Many thanks Mr. Coveney and Mr. Cox !!