Research design and statistics sample question 2

Students who sleep fewer than 5 hours before an exam score lower, on average, than those who sleep 8 hours.

Research design and statistics sample question 3

It is reliable but not valid as a measure of true weight.

Research design and statistics sample question 4

Strength: behaviour is seen in its natural setting. Limitation: variables are not controlled, so causes cannot be established.

Research design and statistics sample question 5

Each participant is her own control, but the fixed order confounds caffeine with practice, so order should be counterbalanced.

MCAT · Psychological, Social, and Biological Foundations of Behavior · Research Methods

Research design and statistics

Research design and statistics is part of Research Methods in the MCAT Psychological, Social, and Biological Foundations of Behavior section. The questions below are written in the style of the real test, each with the answer and a worked explanation.

Question types you will see here include confounds and third variables, internal versus external validity, correlation, causation and regression and sampling methods and selection bias.

Common traps: proposing a variable the design already controls; reversing cause and effect; calling a mediating variable a confound.

Sample questions

Question 1
In a study of aggression, researchers define aggression as the number of times a child hits a toy doll during a 10-minute play session. This definition is:
- A.
  a hypothesis
- B.
  a confounding variable in the study
- C.
  an operational definition
- D.
  an independent variable
Answer: C. an operational definition
An operational definition specifies exactly how an abstract concept will be measured or manipulated in a study, such as counting hits on a doll to measure aggression. A hypothesis is a testable prediction about the relationship between variables, not a specification of how one variable is measured.
Question 2
Which hypothesis is falsifiable?
- A.
  Some people may be happier than others for reasons that science has not yet understood or measured.
- B.
  Unconscious conflicts exist but can never be observed or measured in any way by anyone.
- C.
  Students who sleep fewer than 5 hours before an exam score lower, on average, than those who sleep 8 hours.
- D.
  Fate shapes every life's outcome in ways that always appear random to the people involved in the events.
Answer: C. Students who sleep fewer than 5 hours before an exam score lower, on average, than those who sleep 8 hours.
A hypothesis is falsifiable if some observation could show it is wrong, as with a specific prediction about exam scores (C). The others are vague (A), explicitly unobservable (B) or compatible with any outcome (D).
Question 3
A bathroom scale always reads exactly 2 kg below a person’s true weight, giving the same reading on repeated weighing. Which description is correct?
- A.
  It is reliable but not valid as a measure of true weight.
- B.
  It is valid because it measures weight, but not reliable because readings vary.
- C.
  It is neither reliable nor valid.
- D.
  It is both reliable and valid.
Answer: A. It is reliable but not valid as a measure of true weight.
Identical repeated readings mean the scale is reliable, but a constant 2 kg error means it does not measure true weight, so it is not valid (A). B reverses the two properties. C ignores the consistent readings. D ignores the systematic error.
Question 4
A researcher sits on a bench in a Lagos market for a month, recording how often children share snacks, until the children stop noticing her. Which pair correctly gives a strength and a limitation of this method?
- A.
  Strength: children can be randomly assigned to conditions. Limitation: behaviour occurs in an artificial setting.
- B.
  Strength: behaviour is seen in its natural setting. Limitation: variables are not controlled, so causes cannot be established.
- C.
  Strength: observer effects are eliminated entirely. Limitation: a large sample is required.
- D.
  Strength: cause and effect can be established. Limitation: everyday behaviour cannot be captured.
Answer: B. Strength: behaviour is seen in its natural setting. Limitation: variables are not controlled, so causes cannot be established.
Naturalistic observation offers high ecological validity but lacks control, so it cannot show cause: B. A describes a laboratory experiment; C is wrong because observers can still change behaviour until participants habituate; D reverses both strength and limitation.
Question 5
Thirty volunteers each complete a memory test after taking a placebo on Monday and again after taking caffeine on Tuesday, always in that order. Scores are higher on Tuesday. Which statement correctly describes the design?
- A.
  Each participant serves in both conditions, so both individual differences and order effects are controlled.
- B.
  The design is between-subjects, so differences between the groups of participants confound the result.
- C.
  Each participant is her own control, but the fixed order confounds caffeine with practice, so order should be counterbalanced.
- D.
  The main threat is that volunteers are unrepresentative, which makes the comparison between conditions invalid whatever the order of testing.
Answer: C. Each participant is her own control, but the fixed order confounds caffeine with practice, so order should be counterbalanced.
C is right: a within-subjects design removes individual differences but a fixed order confounds condition with order. A wrongly says order is controlled. B misnames the design. D concerns generalisability, not whether the comparison is valid.

Find your real gaps

A few questions show the style. The free scan shows which MCAT skills cost you the most points, then builds a plan around them.

Take the free scan