Cause to effect progression is seen in all of the following research studies, EXCEPT:

Cause and effect cannot be determined by a case-control study. That is one of it's drawbacks. An ecological study is an epidemiological study in which the unit of analysis is a population rather than an individual. If interesting and strong associations are observed, the results of ecological studies can provide the oppounity for later, more carefully designed studies to build on the initial observations. Coho study is undeaken to suppo the existence of association between suspected cause and disease. Randomized controlled trials are used to examine the effect of interventions on paicular outcomes such as death or the recurrence of disease.