I am struggling with the epidemiological definition of my clinical study design.
Looking at the literature I take it that case-control studies are retrospective (i.e. you must look back on the exposure, simply having cases and controls does not allow you to call the study case-control) while in cross-sectional studies the exposure and outcome are simultaneously assessed.
I have 2 different groups of patients (dementia type A and dementia type B) and one group of controls (no dementia). The studies investigates the association between disease status and some cardiological, neuropsychological and imaging measures, which are taken at enrolment. So my study must be cross-sectional. However, I am using incident cases of dementia (i.e new diagnoses) because we wanted the diagnosis to be homogeneous and thus made at our Centre. Can I call it a cross-sectional study with incident cases and controls?
Can someone help? Thanks!
thank you very much for your detailed reply. It took me a while to get back to you because I had to do a little more research to understand the points you make and see where my problem is. I think I may now have focused it:
1) I am fine with the fact that in cohort studies study groups are defined by exposure and that data collection can be either prospective or retrospective
2) However, in most of the literature I looked up, case-control studies have two characteristics: study groups are selected based on the outcome and data collection is retrospective (e.g doi: 10.1097%2FPRS.0b013e3181f44abc; doi: 10.1089%2Fjpm.2008.9690). In fact for some authors the retrospective nature of the study is fundamental to define it as a case control study and they object that no such thing as a cross-sectional case control study can ever exist (e.g. doi.org/10.1161/CIRCGENETICS.111.959783; by the way this was actually the term I was thinking I would use for my study...); they also maintain that because of its retrospective nature, a case-control study, unlike a cross-sectional study, always allows for (some) causal inference.
3) I do not understand that cross sectional studies are defined based on the outcome. It seems to me that they are simply defined by the simultaneous assessment of both outcome and exposure, precluding any causal inference (e.g. doi:10.1089%2Fjpm.2008.9690, doi:10.4103/0019-5154.182410). However, I am perfectly clear and absolutely agree with what you say about a cross-sectional study with incident (instead of prevalent) cases: it will have the limitation of cross-sectional assessment (direction of causality cannot be determined) but not the bias related to survival.
4) Back to my specific study, I have the impression I am selecting cases and controls based on the outcome (incident dementia or not) and assessing exposure at the same time. So what I call my study appears to depend on the epidemiological definition I use . If case control studies just require selection based on outcome then my study would qualify as a cross sectional case-control study ( which I understand would be epidemiological nonsense..). If, instead, case control studies require both selection based on outcome and retrospective data collection I can only call it a cross-sectional study (data assessment is practically simultaneous).
I would really appreciate if you could follow-up on your response and apologize beforehand if I have made mistakes (PS: as you may have noticed, I am a clinician not an epidemiologist...). Also, I didn't know how post a detailed reply to your comments other than this way, if you or anyone else feels I should instead edit the original post, I will be happy to do so.