Random intercepts
Random intercepts are
- the way the model adjusts the average (fixed) intercept to better match the data from each level of the grouping variable(s).
- one number per level of the grouping variable, which is added on to the fixed intercept to produce the group-specific intercept.
- also called “varying intercepts” or “intercept adjustments”.
- represented by the
1in the random effectlme4syntax:(1 + p | g), wheregis the grouping variable. If a model has only random intercepts bygand no random slopes overp, the random effect term is(1 | g).
To work out whether your model should contain random intercepts, see Identify possible random effects.
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