don't understand output of fitlme, intercept substituted for first line.

Hi - I fit some linear mixed effect models using fitlme , but the output always substitutes 'intercept' for the first line of the fixed effect coefficiants. Why is this?

Fixed effects coefficients (95% CIs):

Name Estimate SE tStat DF pValue Lower

{'(Intercept)' } -1.984e-05 6.4305e-06 -3.0853 37 0.0038374 -3.2869e-05

{'voc_registers_ADS' } -9.3714e-06 6.9456e-06 -1.3493 37 0.18545 -2.3444e-05

{'voc_registers_nonSpeech'} 5.4826e-06 6.4513e-06 0.84985 37 0.40088

Answer 1

[the cyclist]

The output is not substituting 'Intercept' for a level of your coefficient.

It looks like your variable voc_registers is categorical, and has three categories:

• ADS
• nonSpeech
• anotherOne <------ Not possible for me to know the name, from the output

In this case, MATLAB is using 'anotherOne' as the reference category. (This is described in the documentation for fitlme.) By construction, the coefficient of the reference category is zero, and it is not listed in the output.

'Intercept' is the estimate of the mean when continuous explanatory variables are zero, and categorical explanatory variables are at the reference. So, if your model is

'y ~ alpha + beta*voc_registers'

it is the estimate of the value of alpha.

It can be a bit more complicated, if you have both fixed and random effects for the intercept.