11.Types Of Extraneous Variables & Their Controls

Types include:

• Participant variables

• Situational variables

• Demand characteristics

• Experimenter effects

• Placebo effects

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Participant variables

• Personal characteristics that individual participants bring to an experiment & which could influence their responses

• May be biological, psychological &/or social in nature

  Factors include:

• Intelligence

• Memory

• Age

• Diet

• Sleep patterns

• Cultural experiences

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Control

• Aim is to ensure that participants in different experimental conditions are as similar as possible in personal characteristics that may have unwanted influence on the result.

  (with large number of participants)

• Obtaining variables via random sampling to ensure sample is representative of the population being studied

• random allocation to ensure each group will end up with a uniform of spread of participant characteristics in each condition so that the effects of the DV can cancel

  appropriate experimental design, will be dependant on factors such as: Hypothesis being tested, Number of participants available, How the DV will be measured, Practical constraints.

Within subjects design more effective for controlling participant variables as each participant performs under all conditions in experiment

Between subjects design reduce likelihood of differences as random allocation to different conditions will help ensure groups are well matched on participant variables

Situational variables

External factors other than IV associated with the experimental setting that may influence participant response and result.

• background noise

• time of day

• temperature

• presence or absence of other participants

• instructions & procedures used by researcher

Experiment that uses non-standardised instructions & procedures does not strictly control all possible extraneous & confounding variables that can influence DV

Order effect (practice + carryover)

• order effects arising in within subjects are also situational variables

• occur when performance on DV is influenced by specific sequence in which the experimental tasks are presented rather than the IV. Performing one tasks affects performance of the next (can be better or worse)

Practice effects:

• when repeating/prior experience with the tasks can be improve (when participants become more familiar with task) or be impair (due to fatigue, tiredness or boredom) performance

• includes: Test materials, procedures & settings

Carryover effect:

• effects of experiencing task can carry over to next task regardless if task is similar or different

• influences that a particular tasks has on the performance in the task that follows it

eg/ Emotions or substances that may linger in the body may improve or lower performance in later trials.

Control:

Most effective way to control most situational variables is to hold them constant during experiment

• all participants in different conditions must be tested in the same way and in the same situation for experimenter to conclude IV was manipulated by DV

• Should be considered when planning an experiment to ensure they are eliminated, minimised or occur in all conditions if can not be controlled

Control Order Effects:

• Counterbalancing involves systematically changing sequence of treatment or tasks for participants in a balanced way to reduce or avoid unwanted effects on performance of any order

→ can be done by alternating order in which participants or group are exposed to IV

Demand characteristics :

• Cues in an experiment that may influence or bias a participants response

• Cues suggest a kind of response experimenter is wanting or expecting and leads participants to believe they should respond in that way

• may be produced by experimenter or setting

eg/ Participants guessing hypothesis & attempting to act in ways they think will support hypothesis

→ results in non-natural responses to variables in investigation
Control:

Deception, Blind procedures, Experimental Design

• Deception can help ensure participants respond more naturally by concealing purpose of experiment through misleading and misinforming participant.

→ can be used if potential benefits of result outweigh harms

→ there is no other options viable

• single blind procedure keeps participants unaware of experimental conditions they are in

• double blind procedure is where both participants and experimenters who interacting are unaware of conditions in which participants have been allocated, and only researcher that is removed from actual research situation know which participants are in which condition.

  → prevent experimenter cues while controlling participant expectations

Appropriate experimental design

• No within subject designs

• Standardised instructions, minimising cues in environment & ensuring all participants in each conditions have the same experience

• take into account the possibility that participants discuss experiment which they have the opportunity to do so.

Experimenter effect
refers any influence experimenter may have on the results of their investigation

can occur though:

• interaction with participants

• unintentional errors when making observations, measuring responses, analysing or interpreting results

• personal characteristics of the experimenter : Age, gender, Ethnic appearance, Cultural background, Accent, Attitude, Biases, Expectations [ACE-BAGE]

Experimenter Expectancy

• involves cues experimenter provides about responses participants should make in experiment , which can produce a self-fulfilling prophecy.

• Also involves unintentional errors or biases in treatment of data when analysing results (unconscious mistakes)

Actions that may contribute:

• Facial expressions → smiling at one group of participants but not at another

• Mannerisms → shaking hands with participants in one group

• Tone of voice→ speaking differently depending on the group

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Control:

• double-blind procedure

• only researcher or research assistant who has no personal contact with research participants is aware of this information.

• triple blind procedure: Participants, experimenters involved and research assistants are unaware of experimental conditions. Digital technology can keep experimenters blind as to who is in which condition.

• Automating data collection ensures that the score system is consistently & accurately applied

Placebo Effect

• Fake or inactive treatment that substitutes for a real substance

• Change in participants behaviour due to belief that they are receiving some kind of experimental treatment and respond in accordance with that belief rather than the effects of the IV

• to minimise placebo effect on DV, Control group can be given Placebo

• Control should form same expectations as experiment group, controlling effects of unwanted variable