Add Trend/Regression line in tsline

[Michael DeLong]

Hello!

I have three parameters that measure an examiners performance over time. The data is noted for around 10 examiners and is decreases over time, indicating better performance - I already performed analysis with linear mixed model analysis and more.
Now I want to generate a graph plotting the values over time with the following code:

tsset Examiner IndexNumberOfExamination
twoway (tsline PerformanceValue1) (tsline PerformanceValue2) (tsline PerformanceValue3) if IndexNumberOfExamination < 50, by(Examiner)

This already gives me a nice graphical overview but as the performance values are fluctuating a bit, I would like to add a regression or trend-line to visualize decrease. Anyone got an idea how to do that?

Thanks a lot!
Michael

[Nick Cox]

Statistically you have there variables or measures, not parameters. This works with one measure, but I haven't tried it with three.

webuse grunfeld, clear 

tsset company year 

gen log_invest = log(invest) 

twoway tsline log_invest, by(company) || lfit log_invest year

[Michael DeLong]

works great for one measure! But why the log? Just to get a better looking decrease?

[Nick Cox]

That's just for the data example: it works better. Might/might not be true for your data, which I can't see, but I guess you don't need it.

[Michael DeLong]

Thanks a lot!
I have ten "Examiners" and the command with by(Examiner) creates 10 separate graphs.
Now I have a separate variable indicating if the examiner is female or male - is there a way to sort the 10 graphs so that the graphs are sorted by sex?

[Nick Cox]

egen newid = group(female id), label

and then tsset in terms of that.