I am running a longitudinal study which lasted for few months during which

all participants used a specific communicaiton device. I conducted a questionnaire

at the beginning and the same questionnaire was administrated at the end of

the study. All participants performed the same protocol (they

are all using the device). The questionnaire was administrated twice to see if

their answers is going to change because of the device.

The questions are all a 5-level Likrt Scale.

In the analysis; I would like check two things:

1) if there is statistical difference between the answers pre/post study

2) if age and frequency of using the new device has an impact

My data is organized as:

Participant Age Usage Q1Pre Q1Post.......... SumPre SumPost Delta

1 23 45 3 4 20 23 3

...

....

where Delta is SumPost-SumPre

For (1) I know I need to use the Wilcoxson signed rank test since the data is

ordinal (please correct me if I am wrong).

For (2), I am confused! My first question is ; can I treat

SumPre, SumPost and Delta as quantitative variables even though they are extracted

from ordinal/likert scale?

Second question: I could do it one of several ways but not sure which is right (if any

(A) Use Age, Usage and SumPre SumPost

variables: the above variable looks (to me) quantitative, quantitative, quantitative, quantitative

analysis: which I guess means I should be going for Spearman Correlation linear Regression

(B) Use Age, Usage, Delta

variables: The above variable looks (to me) quantitative, quantitative, quantitative

analysis: same as above (I guess)

Or I could introduce categorical variables: AgeGroup and UsageGroup

(C) Use AgeGroup, UsageGroup, SumPre and SumPost

variables: The above variable looks (to me) categorical, categorical, quantitative, quantitative

analysis: not sure?

(D) Use AgeGroup, UsageGroup, Delta

variables: The above variable looks (to me) categorical, categorical, quantitative

analysis: not sure?

I'd appreciate your advise which of A/B/C/D to use and which technique

to use with it?

FYI, I am expecting to see that age and frequency of usage has an effect on the questionnaire result that was administrated at the end of the study.

Best.

Anya