First I would like to appreciate your concern. The basic feachers of cohort whether prospective, ambidirectional or retrospective study is that it starts from exposure so it needs follw up or needs time of followup. But in case of crossectional as the name indicate there is no clear time difference in exposure and outcome that means the investigator collect the data at the same time for exposure and outcome.

In your malaria case the preferable study design is retrospective cohort from your rised alternatives, but if possible prospective cohort also preferable than retrospective cohort.

Martha Nyirenda In the cohort design, you have to be sure that the exposure was before the outcome. In the cross-sectional study, you evaluate exposure and outcome simultaneously. Therefore, in a cohort study you can suspect causality but in a cross-sectional study just can find associations.

Hope this answer could be useful :)

I really appreciate the Question.

The d/ce between retrospective cohort(RC) and Cross sectional study(CSS) is

1. RC Assess the outcome whereas CSS asses both outcome and cause of the out come

2. RC is follow up study, CSS is snap shot/see the situation at a point in time

3. RC can help to formulate cause effect relationship but CSS cant.

4. RC have control group CSS dont

Eg1. If there were 2400 workers in a textile factory before 10 year, (at the begnning of 2012) and if u want to asses how the health status of those workers in the last 10 years look like, weather some die before 8/4/3/2/6 year or are healthy. This is dealt by retrospective cohort.

Eg.2 If u want to study the current prevalence of maleria, then the design is cross sectional. No control group you just prepared you, questionnaire go to area/study participants then ask.

Retrospective cohort, you will ask both exposed and non exposed groups