Question

For each of the abstracts indicate whether the research design is experimental or observational. If Observational, which one (Cross sectional study, Retrospective or prospective study)?

An independent researcher tested the effectiveness of the Atkins weight loss program by randomly selecting 1000 subjects using the program. Each of the subjects was called to report his or her weight before the diet and after the diet.

Phase II of the Nurses’ health Study was started in 1989 with 116,000 female registered nurses. This study is ongoing.

Sample of subjects with and without heart disease were selected, then researchers looked back in time to determine whether they took aspirin on a regular basis.

Researchers from the National Institutes of Health want to determine the current rates of marijuana consumption among adults living in states that have legalized the use of marijuana. They conducted a survey of 500 adults in those states.

The Physicians’ health Study involved 22,071 male physicians. Based on random selections, 11,037 of them were treated with aspirin and the other 11,034 were given placebos.

Answer 1

Experimental research design - we set up the experiment. We have the following requirements for a successful experimental research design: Random Participant selection and random assignment of participants to control group, and control over all extraneous variables.

Observational research design, as the name suggests involves direct observation of individuals in their natural habitat. There are three types:

1. Cross sectional studies : Exposure and outcome are determined simultaneously for each individual. Used to understand the prevalence of various conditions and treatments,

2. Retrospective : As name suggests, it looks backwards, and examines exposure to risk under consideration in relation to an outcome which was established at the onset of the study.

3. Prospective : It watches for outcomes, such as development of disease during the study period and then relates that to the suspected risk.

Now back to the question

1. An independent researcher tested the effectiveness of the Atkins weight loss program by randomly selecting 1000 subjects using the program. Each of the subjects was called to report his or her weight before the diet and after the diet.

Observational research design - Prospective

Here we know the outcome, weight loss and we are trying to figure out if the suspected risk i.e. Atkins weight program is responsible for it.

2. Phase II of the Nurses’ health Study was started in 1989 with 116,000 female registered nurses. This study is ongoing.

Observational research design - Prospective

3. Sample of subjects with and without heart disease were selected, then researchers looked back in time to determine whether they took aspirin on a regular basis.

Observational research design - Retrospective

Here we looks backwards, and examines whether aspirin was taken when samples of subjects with and without heart disease were selected.

4. Researchers from the National Institutes of Health want to determine the current rates of marijuana consumption among adults living in states that have legalized the use of marijuana. They conducted a survey of 500 adults in those states.

Observational research design - Cross sectional studies

Here we are trying to figure out the marijuana consumption among adults that have legalised the use.

5. The Physicians’ health Study involved 22,071 male physicians. Based on random selections, 11,037 of them were treated with aspirin and the other 11,034 were given placebos.

Experimental research design