Hello there,
I'm doing a module in research methods and we are required to analyse some data (provided to us) from a randomised control trial.
I'm having some difficulty deciding on what stats analysis to do...
Background: the primary outcome measure is the sum of scores from a 36 item 'disability questionnaire' (the dependent variable). Each item on the questionnaire asks participants to rate the difficulty they have performing an everyday task. They have 3 options which are attributed a score - no difficulty (0), some difficulty (1), unable to do (2). They end up with a score out of 72. This is done at baseline (time 0). Participants are then randomised to receive an intervention group or a control group (independent variable). After a couple of days, both groups repeat the questionnaire (time 1).
The main research question is, does the intervention reduce disability (which would be evidenced by a significantly greater decrease in questionnaire score in the intervention group than in the control group).
My questions are:
1) what type of variable is the sum of the scores of the questionnaire? Reading around this I can't find any clear guidance. Some sources say Likert-type scales are strictly ordinal data but then could the sum of Likert-type scale scores be classed as interval data?
2) what test should be used to assess for a between-group difference in disability score between time 0 and time 1? My stats textbooks aren't very clear on this!
Many many thanks in advance!
I'm doing a module in research methods and we are required to analyse some data (provided to us) from a randomised control trial.
I'm having some difficulty deciding on what stats analysis to do...
Background: the primary outcome measure is the sum of scores from a 36 item 'disability questionnaire' (the dependent variable). Each item on the questionnaire asks participants to rate the difficulty they have performing an everyday task. They have 3 options which are attributed a score - no difficulty (0), some difficulty (1), unable to do (2). They end up with a score out of 72. This is done at baseline (time 0). Participants are then randomised to receive an intervention group or a control group (independent variable). After a couple of days, both groups repeat the questionnaire (time 1).
The main research question is, does the intervention reduce disability (which would be evidenced by a significantly greater decrease in questionnaire score in the intervention group than in the control group).
My questions are:
1) what type of variable is the sum of the scores of the questionnaire? Reading around this I can't find any clear guidance. Some sources say Likert-type scales are strictly ordinal data but then could the sum of Likert-type scale scores be classed as interval data?
2) what test should be used to assess for a between-group difference in disability score between time 0 and time 1? My stats textbooks aren't very clear on this!
Many many thanks in advance!