[R-meta] Effect size measure for count data

[Sarah Schaefer]

Dear colleagues,

We are currently planning an individual-patient-data meta-analysis on the effect of post-trauma sleep on symptoms of posttraumatic stress disorder (i.e., number of intrusions). For this purpose, we have data of seven analogue studies that assess intrusion frequency as a count variable using intrusion diaries or experimental triggering tasks. Number of intrusions per study are our primary outcome. Events (intrusions) regularly occur more than ones per participant. Our data follows a Poisson or a binomial-negative distribution (as we are still waiting for one dataset to finally check dispersion). For our IPD analysis we use a multilevel model which accounts for between-study heterogeneity on level 2. However, there is at least one study for which we do not have IPD. Therefore, we want to present both, a one-step approach IPD (using the multilevel model) and an analysis based on aggregated data (i.e., traditional meta-analysis). Now we a struggling finding an appropriate effect size measure for the latter analysis. We aim to compare sleep and wake groups but I do not think that standardized mean differences would be an appropriate measure as they assume data to follow a normal distribution. However, looking into effect size measures for count data (within metafor), these are related to specific time intervals or group sizes. Due to different experimental designs (intrusion diary and intrusion triggering task) and the occurrence of multiple events per participant these are not applicable in our case. Therefore, we wanted to ask if anyone has an idea how to solve this issue (within metafor or other meta-analysis R packages). We would need an effect size measure for group differences in count data that allows for multiple events per participant (number of events > number of participants per group).

Kind regards and thank you very much on advance,
Sarah




Aufsichtsratsvorsitzende: Dr. Carola Zimmermann,
Geschaeftsfuehrer: Prof. Dr. Klaus Lieb, Prof. Dr. Beat Lutz (wissenschaftlich), Dr. Thorsten Mundi (kaufmaennisch).
HRB 48032, Amtsgericht Mainz

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