ECON30500 Field Experiments: Unit Two

What is random assignment?

Any procedure that assigns units to conditions based only on chance, where each unit has a non-zero probability of being assigned to a condition. It must be purely by chance, and cannot be based on any systematic characteristics. Alternating is not random.

What is random sampling?

Selecting units from a population of interest in a randomised manner to create a sample that is representative of the population.

What is the difference between random assignment and random sampling?

Random sampling is used to obtain a sample of people so you can infer the results to a wider population. Random assignment is when units are assigned randomly to treatment and control groups.

What is external validity?

The acceptability of results in contexts other than those in which the experiment was conducted. This occurs due to random sampling.

What is internal validity?

The acceptability of the results within the causal impact of the intervention, essentially that the results accurately reflect the studied group and are not caused by methodological issues. This occurs due to random assignment.

What can be randomized?

• Access: Which participants are offered access to a program.

• Timing: When participants are offered access to a program.

• Encouragement: Which people are given encouragment to participate.

What constraints to randomization do we have?

• Must be percieved as fair

• Must be politically feasible

• Must be ethical

What is a basic lottery design?

A randomization strategy in which a lottery decides who enters the treatment from the applicant pool. Use this method when the program is oversubscribed.

What are the advantages of a basic lottery design?

• Familiar

• Transparent

• Easy to understand and implement

• Percieved as fair

What are the disadvantages of a basic lottery design?

• Control group may not cooperate

• Differntial attition

What to do when a program has strict eligibility criteria?