# [R] How to interpret lm's coefficients?

Matti Viljamaa mviljamaa at kapsi.fi
Thu Sep 8 14:43:55 CEST 2016

```I’m trying to understand how to interpret the return values, specifically “Coefficients:”, of R’s lm function. I’m using it with a dichotomic predictor (mom_hs).

lm(data\$kid_score ~ data\$mom_hs) returns

Coefficients:
#   (Intercept)  data\$mom_hs
# 77.55        11.77

I read that the (Intercept) value is the “y-intercept” value b, i.e. the y value where the line intercept the y-axis.

The second value is the value of the term m (or “slope”) in the equation of a line y=mx+b.

However,

These two numbers also have the following interpretations:

b or (Intercept) value is the same as:
The mean of those data\$kid_score that have data\$mom_hs == 0.
Why is this a valid interpretation?

m or data\$mom_hs value is the same as:
The difference of means between those data\$kid_score that have data\$mom_hs == 1
and those data\$kid_score that have data\$mom_hs == 0.
Why is this a valid interpretation?

Can someone explain?
```