error help: at level for factor var not present in estimation

[em lowthian]

Hi everyone,

I'm having trouble understanding what an error code means when running the margins command for a logistic regression I have ran.
The logistic and margins code is:

logistic r_ks4_level2_em_37 i.r_mo_ligmodheavyalc_9 i.r_mo_highestedqual_4  i.r_mo_drugsyn_9 i.r_mo_nosmokedlast2wk_3 i.r_mo_alccon1stmove_3 i.r_mo_prenataldrugyn_3  i.r_mo_familyincomeweek_9 i.r_mo_anxietydr_9 i.r_mo_depressiondr_9 c.r_mz028b i.cr_mo_ethnicgrp_4 i.r_mo_ligmodheavyalc_9#i.r_mo_highestedqual_4

margins r_mo_ligmodheavyalc_9, at(r_mo_highestedqual_4=(1(1)6)) 
marginsplot, noci ytitle(KS4 outcomes) name(alcoholqual6gcse5ACengmath)

The error says

  at level for factor r_mo_highestedqual_4 not present in estimation

I've looked at the Stata guide and looked online but I can't seem to make sense of this error. The size of the regression is 5, 700 observations. The alcohol category has 3 category's (no drinking, light drinking, moderate drinking and heavy drinking) and the qualifications variable has 6 categories (no qualifications, CSE, skilled qual, O-level, A-level or equivalent and degree).

Hope this is enough information,

Emily

[William Lisowski]

Stata is telling you that in your estimation sample - which includes only observations with no missing values on any of the variables - at least one of the values you specified for r_mo_highestedqual_4 does not appear. Try adding the following before the margins command.

tab r_mo_highestedqual_4 if e(sample)

[em lowthian]

Hi William!

Thanks for this!

Emily

[Clyde Schechter]

Some additional advice beyond William's. Since r_mo_highestedqual_4 is a discrete variable in your model, you don't need to use an -at()- option here. The simpler way to get the results you want is just:

margins r_mo_highestedqual_4#r_mo_ligmodheavyalc_9

Stata will then give you the expected outcome probabilities at all combinations of those two variables that actually exist in the estimation sample.

[em lowthian]

Clyde - this will save time, fantastic. Thank you very much.