I have measurement items like (just as an example):
"Having taken medicine A ....
- I felt that I am feeling better
- I felt that it helped me
- I felt that it is necessary to take it again
- I felt that I might need it
Each of the four items were measured on a 7 point likert scale with "1 = Not at all" ... "4 = Neutral" ... to "7 = Very much". How can I merge them into one construct (named for instance) "effect level"? And how can I check for reliability?
I am using SPSS if that is necessary.