[iebaltab] - allow for multiple stats per stats type

[kbjarkefur]

For example, stats(pair( beta se)) would show both Beta and the standard errors.

This is not possible today, but the introduction of stats() was the first step towards allowing the in an later version.

[kbjarkefur]

@bbdaniels original comment in https://github.com/worldbank/ietoolkit/issues/288#issuecomment-1251521529_

Ok I have looked through this now and it looks hugely improved, great work! I just have one last question, which is, how can I request a mean and a variance statistic for the pairwise comparisons at the same time (ie, beta and p)? That is the only thing I would want to do that I can't figure out and there appears to be room in the table for that where there are currently blank spaces.

For example, I run:

iebaltab pop medage, grpvar(region) savex("/users/bbdaniels/desktop/test.xlsx") replace stats(pair( beta ))

And get:

But this fails, so it is not clear how to fill the blanks (as in K5):

.  iebaltab pop medage, grpvar(region) savex("/users/bbdaniels/desktop/test.xlsx") replace stats(pair( beta se))

The [pair(beta se)] in [stats(pair( beta se))] is not formatted properly. Make sure that each test name is follewed by a single stat inside a ().
invalid syntax
r(198);

[kbjarkefur]

As suggested in https://github.com/worldbank/ietoolkit/issues/295. Consider adding multiple stats in extra columns rather than extra rows as in Mean/SE in the screen shot above.

I think it is important that we only allow row/column to be an option if it can be done without making the command too complex. That is what lead to iebaltab to need a re-write in the first place. In the post re-write version there is also the result matrix and from that any user can create tables with infinite amount of customization.