A doctor studies the relative effectiveness of two drugs of dengue fever. His…

Concept: Research methods are classified by what the investigator does with the variables. In experimental research the investigator deliberately manipulates an independent variable (the treatment), keeps the remaining conditions comparable, and measures the effect on a dependent variable; that control over the treatment is what allows a cause-and-effect claim. Methods that only record phenomena as they already occur describe a situation instead of manipulating it.

Application to this study:

1. What a comparison of relative effectiveness requires: both drugs must be given to comparable dengue patients and the resulting outcomes set against each other, so the drug received is the variable whose two levels the study compares.

2. Independent variable: which of the two drugs a patient receives. Under the controlled drug-comparison design that this classification assumes, that assignment is made as part of the study rather than being a pre-existing patient characteristic that is only recorded.

3. Dependent variable: the clinical outcome measured afterwards, such as fever clearance or time to recovery, observed under each of the two drug conditions.

4. Control: for a difference in outcome to be attributed to the drug, the two sets of patients must be kept comparable in other respects and measured by the same protocol, so control of extraneous variables belongs to this design.

5. Treatment applied, other conditions held comparable, outcomes compared - that combination is the defining signature of experimental research, so the study is classified as Experimental Research.

Cross-check against the other methods:

• Descriptive survey: characteristics, opinions or practices are collected from a sample as they already exist; nothing is administered, so the relative effect of two drugs cannot be isolated.

• Case study: a single unit is examined in depth; there is no second condition against which its outcome can be compared.

• Ethnography: prolonged fieldwork describes a community's culture and shared practices; it is descriptive and qualitative rather than a controlled comparison.

Note on what the stem states: it gives the aim rather than the procedure, and it does not say whether the doctor himself assigned patients to the two drugs; relative effectiveness can in principle also be studied observationally. Experimental Research is the official and intended best answer among the four methods offered, read under an assumed controlled drug-comparison design, and the stem by itself does not settle who allotted the treatments. Of the four methods offered, only the experimental method is built on administering treatments and comparing their outcomes.

Result: the study is Experimental Research; a two-arm comparative drug trial is its classic form.