1D Preventing error and bias

Extraneous variable: any variable that is not the independent variable but may cause an unwanted effect on the dependent variable

• e.g. mnemonics study
• IV: use of mnemonics
• DV: information retention
• EV: teacher performance, school resources, student interest

• Confounding variable: a variable that has directly and systematically
• affected the dependent variable, apart from the independent variable.

• e.g. mnemonics study
• IV: use of mnemonics
• DV: information retention
• EV: teacher performance, school resources
• CV: student interest -  results evidently influenced

• • participant-related variables
• • order effects
• • placebo effects
• • experimenter effects
• • situational variables
• • non-standardised instructions and procedures
• • demand characteristics.

Participant-related variables: characteristics of a study’s participants that may affect the results.

e.g. age, intelligence, socioeconomic status

Order effects: the tendency for the order in which participants complete experimental conditions to have an effect on their behaviour.

• • practise effects - perform better in later conditions due to
• having done it before

• • fatigue effects - perform worse in later conditions due to being
• tired or bored from completing a prior task.

• Placebo effect is when participants respond to an inactive substance
• or treatment as a result of their expectations or beliefs.

Participants’ responses are not due to the chemical properties of a substance taken, intervention, or their experimental condition, but rather how they believe it should make them feel or act.

Experimenter effect is when the expectations of the researcher affect the results of an experiment.

• Situational variables are any environmental factor that may affect the
• dependent variable.

• Non-standardised instructions and procedures is when
• directions and procedures differ across participants or experimental conditions.

• Preventing extraneous and confounding variables: 
• • Sampling size and procedures 
• • Counterbalancing 
• • Placebo 
• • Single-blind procedures 
• • Double-blind procedures 
• • Standardised testing conditions and procedures 

• Sample size and procedures:
• Having a large sample size increases the likelihood of producing a sample that has a similar level of diversity as it does in the population - more likely to be unbiased

• Counterbalancing is a method to reduce order effects that involves
• ordering experimental conditions in a certain way.

• e.g. splitting participants into two groups
• Group 1: Condition A -> Condition B
• Group 2: Condition B -> Condition A

Placebo is an inactive substance or treatment, such as a sugar pill.

Experiments may include two experiemental groups with one group receiving the active substance/intervention while the other is given a placebo. Helps researchers understand how significantly an active intervention may affect individuals (doesn't stop placebo effect).

• Single-blind procedure: a procedure in which participants are unaware
• of the experimental group or condition they have been allocated to.

• Double-blind procedure: a procedure in which both participants and
• the experimenter do not know which conditions or groups participants are
• allocated to - research assistant may do allocation instead

Standardised testing conditions and procedures ensures that each participant receives the exact same instructions and procedures in each condition, allowing researchers to more conclusively infer that results are due to the independent variable.