I am analyzing data from a mindfulness intervention in which 60 participants took part in an ipod-based intervention listening to meditation tracks. Outcome measures on anxiety, depression, stress, health etc. were collected pre and post intervention. There was no control group.
I have been advised to use an ANCOVA to answer my research question-- (Does listening to meditation tracks reduce stress/anxiety/depression?) Where the independent variable is Total Time Spent Listening (varies per participant from 0 minutes to 1000 minutes depending on their interest and level of participation) and the dependent variable is post-intervention outcome measure scores with the covariate as the pre-intervention scores.
I'm wondering if this is the best way to analyze this data--as we are interested in seeing a potential dose-response effect for those who listening to more tracks and simply looking at t-tests wouldn't allow for this analysis.
I have read that an assumption of ANCOVA is that the DV and covariate are independent (not correlated) which would obviously be violated in this design, although I have seen plenty of papers published anyways. Is this an issue I need to be aware of?