Doubts in applying Linear Regression

linear_regression
r
data_science

#1

Hi,

My data,

 Exercise Econ  Job Position
       50    1    A    Owner
       30    0 <NA>     <NA>
       25    1    B Employee
       44    1    B    Owner
       32    0 <NA>     <NA>
       50    0 <NA>     <NA>
       22    1    A Employee
       14    1    C Director

lm(formula = Exercise ~ Job + Position)

The coefficients comes as
Coefficients:
(Intercept) JobB JobC PositionEmployee PositionOwner
50 3 -36 -28 NA

My Question is,

  1. Why “NA” for PositionOwner ? and How do i resolve it ?
  2. When i change the value to “C” for exercise “44” then i am not getting NA for postiionOwner ?
  3. Generally, how can i dealt these NA in coefficents for factor variables ?

Regards,
Nantha.


#2

Actually the Formula is lm(formula = Exercise ~ Econ+Job + Position)

Data in formatted way,
Exercise Econ Job Position
50----------1-------- A--------Owner
30----------0-------NA-------NA
25----------1---------B-------- Employee
44----------1---------B-------- Owner
32----------0---------NA-------NA
50---------0-----------NA----------NA
22---------1----------NA----------Employee
14--------1-----------C----------- Director