My Question is how to use HLM in a daily diary study to answer the research question.
The study design is as follows:
14 days of measurement to capture within-person variability in mood, impulsive behaviors, etc (1 measure per day)
2 cortisol samples are taken each day, at waking and then 30 min later(2 measures per day - actually there are 4 since each sample is split and analysed separately for reliability. I use these as split scales so I can model the linear change in cort from waking to 30 min later. this parameter is of particular interest to the PI on the study and is the one I'm having trouble with). My baseline Level 1 model is
Cortij = B0j + B1jTime + B2jcDay7 + rij
(The B2 term is just to control for any potential linear effect of days per Bolger and Laurenceau- I account for it but it's non-significant)
The research questions relate to how within-person fluctuations in mood/impulsive behaviors predict BOTH waking cort level and the slope from waking to 30 min later (Time coded 0 1). As an example: "When a person drinks more than their personal average, is there an associated increase in waking cortisol, or a steeper increase in cortisol from waking to 30 post waking?"
I thought putting in the person-centered predictor (in this example drinks), and then an interaction of the person centered drinks variable with time at Level 1, might give me my answers, but a colleague has indicated this is not correct. Any modeling suggestions to answer the above design question are most appreciated.
Thank you,
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