`I'm trying to use interaction terms in lm and for the following types of`

`models:`

`fit3_hs <- lm(kidmomhsage$kid_score ~ kidmomhsage$mom_age +`

`kidmomhsage$mom_hs + kidmomhsage$mom_age * 1)`

`fit3_nohs <- lm(kidmomhsage$kid_score ~ kidmomhsage$mom_age +`

`kidmomhsage$mom_hs + kidmomhsage$mom_age * 0)`

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`where you see the last term being the interaction term (it's`

`mom_age*mom_hs where mom_hs takes values 0 or 1), the results are`

`causing a bit of confusion.`

fit3_hs returns: Call:

`lm(formula = kidmomhsage$kid_score ~ kidmomhsage$mom_age +`

`kidmomhsage$mom_hs +`

kidmomhsage$mom_age * 1) Coefficients: (Intercept) kidmomhsage$mom_age 70.4787 0.3261 kidmomhsage$mom_hs 11.3112 fit3_nohs returns: Call:

`lm(formula = kidmomhsage$kid_score ~ kidmomhsage$mom_age +`

`kidmomhsage$mom_hs +`

kidmomhsage$mom_age * 0) Coefficients: kidmomhsage$mom_age kidmomhsage$mom_hs 3.368 11.568 Now why is (Intercept) term missing from the second one?

`Also since in the first one the interaction term's coefficient should be`

`added to the coefficient of mom_age, then is the return value of`

`kidmomhsage$mom_age 0.3261 the sum of the coefficient of mom_age and the`

`coefficient of the interaction term? Or would I need to produce the sum`

`myself somehow?`

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