The Experimental Design

In one line

An experiment changes one thing deliberately and holds the rest constant, so that any difference in the result can be attributed to the change, and that is the only design that establishes causation directly.

In the wording a student can write in an exam: the experimental research design tests a causal hypothesis by manipulating an independent variable and observing its effect on a dependent variable while controlling other influences, usually by comparing an experimental group which receives the treatment with a control group which does not; its distinguishing feature is manipulation, which neither the descriptive nor the diagnostic design employs, and it is rarely available in legal research because the law cannot ordinarily be applied to one group and withheld from another.

The elements

The independent variable, which the researcher changes: the treatment.

The dependent variable, which is measured to see whether it changed.

The control, being everything else held constant so that it cannot explain the difference.

The experimental group, which receives the treatment, and the control group, which does not.

And randomisation, assigning units to the groups by chance so that the groups do not differ systematically to begin with. This is what makes an experiment powerful, and it is usually the element that cannot be had in legal research.

Why law rarely permits it

Because withholding the law from a control group is not permissible. A study of whether informing an accused of the right to legal services improves outcomes cannot inform half of them and deliberately not inform the other half. The duty exists for all of them, chapter 630.

Because the units are people in real proceedings, whose interests cannot be subordinated to a research design, chapter 1400.

Because the legal system does not hold anything else constant. Two courts differ in every respect at once.

And because the effects are slow. A change whose consequence appears over years cannot be studied in a semester.

What is available instead

Four designs that approach the experiment without manipulating anybody's legal position, and a student should know them because they are the realistic options.

The before-and-after study. Measure, wait for a change that somebody else makes, measure again. If a District Authority establishes a clinic in a settlement, applications from that settlement before and after are a natural comparison.

Its weakness. Anything else that changed in the interval is an alternative explanation, so the design needs a reason to think nothing else did.

The comparison of comparable units. Two similar taluks, one with a clinic and one without. Not an experiment, because the assignment was not random, but a real comparison if the two are genuinely alike.