Hello there,

I am doing a research to validate a questionnaire about general health. The questionnaire has two sub-scales: physical health and mental health. My question is about checking the agreement of the mental health sub-scale only with other reference questionnaires (one about anxiety (GAD-7) and one about depression (PHQ-9).

The mental health sub-scale consists of 4 questions with a 5 Lickert scale. The raw points are summed then converted into T-scores with a mean of 50 and a standard deviation of 10.

I want to check the agreement between this questionnaire and the PHQ-9 that has 9 questions and 4 lickert scale!

So is it ok to measure the agreement level between the two instruments? or do they need to have the same scale?

Regards,

Burhan