How to interpret R linear regression when there are several levels of factors as the baseline?

Question

My data has 3 independent variables, all of which are categorical:

condition: cond1, cond2, cond3

population: A,B,C

task: 1,2,3,4,5

The dependent variable is the time the task completed. I run lm(time~condition+user+task,data)in R and get the following results:

What bothers me is that cond1, groupA and task1 are not taken into account. From linear regression, “NA” is estimated only for the last coefficient , I understand that one factor level is selected as “base” and shown in the line (Interception).

But what if several factors are used as the baseline, as in the above case?

• Does the line (Interception) show cond1 + groupA + task1?
• , cond1, groupA task1 ?
• , groupB +9.3349 groupA? cond1 + groupA + task1?

Answer 1

"", "" "", ; cond1, A t1. () , cond1, groupA task1.

cond1, groupA task1 , . .

, B , - B 9.33 (?) , - A, , , p- , , B (A). , (, usergroupB:taskt4) ( ) , ( , B 4). (usergroupB taskt4).

, .

Answer 2

() cond1 + groupA + task1?

.

, cond1, groupA task1 ?

, . . , . , (. multcomp).

, B +9.3349 GroupA? cond1 + groupA + task1?

cond1/task1/groupA cond1/task1/groupB. ( @Rufo, , , groupB groupA , .)

Answer 3

R . , . .

cond1 condition, A population 1 task. .

- .

, conditioncond2 - cond2 cond1, population - A task - 1. , , , . (, conditioncond3 - cond3 cond1.)

The same is true for other factors. Effects populationare saved only for condition cond1and task 1. Effects taskare saved only for condition cond1and population A.