Experimental Design

Making a causal conclusion possible.

12 problems · about 21 minutes · VAR-3.C, VAR-3.E

What this lesson teaches

The student identifies the principles of experimental design and evaluates a study.

Straightforward practice. Get the method working first.

5 problems

Grouping similar subjects before randomising within each group is called what? 1 blocking, 2 blinding.
Answer 1
Why Blocking.
Why does random assignment permit a causal conclusion?
Answer It balances every other difference, known and unknown, across the groups.
Why Other differences even out.
A group receiving a fake treatment is called what? 1 control, 2 treatment.
Answer 1
Why The comparison group.
Grouping similar subjects before randomising is called what? 1 blocking, 2 blinding.
Answer 1
Why It removes a known source of variation.
Does blocking raise power? 1 yes, 0 no.
Answer 1
Why Less unexplained variation.

The same ideas with more to keep track of.

3 problems

Can an observational study alone establish causation? 1 yes, 0 no.
Answer 0
Why Confounding remains possible.
A variable changing alongside the treatment is called what? 1 confounding, 2 blocking.
Answer 1
Why Its effect cannot be separated.
How many principles of design were listed?
Answer 4
Why Comparison, randomisation, control, replication.

Mixed problems. Work out what kind of question it is before you start.

4 problems

Which features belong to a well-designed experiment?
Answer Random assignment to treatments; A control group; Enough subjects per group
Why Self-selection destroys the causal conclusion.
Subjects improve from believing they were treated. Placebo effect? 1 yes, 0 no.
Answer 1
Why Belief alone.
The Licence: What licenses a causal conclusion? 1 random assignment, 2 a large sample.
Answer 1
Why Random assignment.
The Blinding: Neither subjects nor measurers know the groups. Double blind? 1 yes, 0 no.
Answer 1
Why Yes.