All subjects · Psychology · WPS04 Clinical Psychology and Psychological Skills

Control issues in research

Edexcel IAL Psychology · WPS04 Clinical Psychology and Psychological Skills

Spec 9.1.10 covers control issues: counterbalancing, randomisation, order effects, experimenter and researcher effects, social desirability, demand characteristics, participant, situational, extraneous and confounding variables, and operationalisation.

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Variables

Extraneous variables: any variable other than the IV that might affect the DV.
Confounding variables: extraneous variables that do affect the DV and vary with the IV, so the results cannot be put down to the IV (for example, drug type in Suzuki et al.).
Participant variables: individual differences (age, personality, severity of illness).
Situational variables: features of the setting (noise, time of day, instructions).
Operationalisation: defining variables so they can be measured (for example underweight = BMI under 18.5).

Order effects and how to control them

In repeated measures designs, performance may change because of the order of conditions: practice, fatigue or boredom.

Counterbalancing: half the participants do A then B, half do B then A (Reichel et al. counterbalanced two picture sets).
Randomisation: the order of conditions or stimuli is random; random allocation to groups controls participant variables.

Effects of being studied

Demand characteristics: participants guess the aim and change their behaviour. Control: single-blind procedures, deception (with debriefing), covert observation.
Social desirability: giving answers that make you look good, a risk in self-report on mental health. Control: anonymity, physiological measures (Reichel et al.).
Experimenter/researcher effects: the researcher's expectations influence results (for example through cues or biased recording). Control: double-blind procedures, standardised instructions, inter-rater checks.

Worked example

In a repeated measures study, participants recall words in silence and then with music. Identify the problem and how to fix it.

Problem: order effects. Participants may do better in the second condition through practice, or worse through fatigue.
Fix: counterbalance, with half doing silence first and half music first.
Order effects then balance out across conditions, so differences are more likely due to the IV.

Answer: Order effects, controlled by counterbalancing.

Key idea: Extraneous and confounding variables (participant, situational); operationalisation; order effects controlled by counterbalancing and randomisation; demand characteristics, social desirability and experimenter effects controlled by blind procedures, anonymity, standardisation and objective measures.

Check yourself

What is counterbalancing?
- Half the participants do the conditions in one order and half in the reverse order
- Randomly choosing participants
- Matching participants on age
- Hiding the aim from participants
Show answer
Half the participants do the conditions in one order and half in the reverse order. Balances order effects.
What makes an extraneous variable a confounding variable?
- It is measured by the researcher
- It is the IV
- It varies with the IV and affects the DV
- It has no effect
Show answer
It varies with the IV and affects the DV. Confounds systematically vary with the IV.
Which best controls demand characteristics?
- A single-blind procedure where participants do not know the condition they are in
- Using a larger sample
- Counterbalancing
- Stratified sampling
Show answer
A single-blind procedure where participants do not know the condition they are in. If participants do not know, they cannot act on the aim.
Answering a questionnaire about mental health in a way that makes you look good is
- an order effect
- a situational variable
- counterbalancing
- social desirability
Show answer
social desirability. Social desirability bias.
Which is the best operationalisation of 'improvement in depression'?
- Feeling better
- A reduction in score on a standardised depression questionnaire after 12 weeks
- Being happier
- The therapist's impression
Show answer
A reduction in score on a standardised depression questionnaire after 12 weeks. Measurable and specific.
Explain how a double-blind procedure reduces researcher effects in a drug trial.
Show answer
Because the researchers measuring outcomes do not know which participants received the drug or placebo, their expectations cannot bias how they treat participants or record results.. Researchers unaware of conditions cannot bias results.

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Last updated 8 November 2026. Spotted a mistake? Tell us.