Syntax for fitlm: + versus *

What is the difference between the following syntax:

model(10).results = fitlm(tbl,'Acceleration ~ id * Weight');

and

model(10).results = fitlm(tbl,'Acceleration ~ id + Weight');

I am trying to run a linear model but allowing the intercept to vary per the "id" or identity of each observation.

Many thanks!

Answer 1

[Walter Roberson]

https://www.mathworks.com/help/stats/fitlm.html#bt0ck7o_sep_shared-DefinitionWilkinsonNotation

id + Weight includes both id and Weight as linear terms, it appears.

id * Weight includes id, Weight, and id times Weight terms, if I understand correctly.

[Lydia]

Thank you very much!