EXPERIMENTS

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EXPERIMENTS

• Psychological Research method

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Key Terms ExperimentsPlease complete these
definitions on your worksheet as you go

• Laboratory Experiment
• Field Experiment
• Quasi Experiment
• Independent Variable
• Dependent Variable
• Control of variables
• Confounding Variable
• Extraneous Variable
• Replication
• Cause and Effect
• Ecological Validity
• Demand Characteristics

• Ethics
• Informed consent
• Right to withdraw
• Independent Measures
• Repeated Measures
• Matched-Pairs
• Counter Balancing
• Operationalising Hypothesis
• Alternative Hypothesis
• Null Hypothesis
• descriptive statistics (mean, median, mode,
  range)
• bar chart

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Experiments

• Three types of experiments
• Laboratory experiments
• Highly controlled / artificial
• Field experiments
• Controlled variables in a natural environment
• Quasi (natural) experiments
• We have no control over the independent variable
  its naturally occurring (eg Gender)

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Experiments
Independent Variable (IV)
Dependent Variable (DV)
Confounding Variable a variable that effects the
DV Extraneous Variable a variable that could
affect the DV but has been controlled for so it
doesnt.
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Experiments

• Extraneous Variables
• Participant Variables
• Independent Measures Individual Differences
• Situational Variables
• Any feature of the experiment that could
  influence a participants behaviour
• Single Blind Double Blind Control Groups

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Experiments Hypotheses
How are we measuring memory?
Whats better or worse? Higher / Lower? More /
Less?
Participants memory will be much worse when there
is a distraction in the room than when there is
no distraction.
Participants memory will be much worse when there
is a distraction in the room than when there is
no distraction.
What is the distraction? How are we manipulating
it?
Operationalising your hypothesis How have you
manipulated your IV? How have you measured your
DV?
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Experiments Hypotheses
Participants memory will be much worse when there
is a distraction in the room than when there is
no distraction.
Participants will remember significantly more
words from a list of 20 presented for 60 seconds
when they are in a room with no distractions than
participants who are in a room where rock music
is playing in the background.
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Experiments Hypotheses
Participants who do something will be
significantly faster/better/quicker etc at
something than participants who do something
else. There will be no significant difference
between participants who do something and those
who do something else. Any difference will be
down to chance.
Alternative
Null
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Experiments Hypotheses
Participants who do something will be
significantly faster/better/quicker etc at
something than participants who do something
else. There will be a significant difference
between participants who do something and those
who do something else.
1Tailed
2Tailed
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Sampling
General Population
Representative Sample Generalisations Sampling
Techniques
Sample
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Sampling

• Opportunity Sample
• People who are there at the time.
• Quick / Cheap / Easy
• Not representative

• Random Sample
• Each person in the GP has an equal chance of
  being chosen.
• Expensive and time consuming.
• Representative sample

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Sampling

• Self-Selected
• Participants volunteer to be in the sample
  following advert etc.
• Quick / Cheap / Easy
• Not representative
• What kind of person volunteers for a psychology
  experiment?

• Snowball Sampling
• One person tells others who tell others
• Allows us to collect difficult to locate people
• Time consuming

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Experiments

• Independent Measures
• Participants are only in one condition.

• Repeated Measures
• The same participants repeat the two conditions

Condition 1 Condition 2
Condition 1 Condition 2
Counter balancing alter order of Pps
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Experiments

• Matched Pairs make two groups of participants
  as similar as possible.

Condition 1
Condition 2
Male (Bob) 21 IQ 105
Male (Richard) 21 IQ 105
Female (Dawn) 25 IQ 115
Female (Cara) 25 IQ 115
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Strength Weakness
Independent Measures No Order Effects Fewer Demand Characteristics Individual Differences
Repeated Measures No Individual Differences Order Effects (counter balancing)
Matched Pairs Controls for Individual Differences Can be difficult and costly.
Evaluation of Experimental Designs
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Ethics

• Consent
• Withdrawal
• Debriefing
• Deception
• Confidentiality
• Observation
• Protection

• Advice
• Colleagues

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Data Analysis
Scattergram to show the Correlation between
variable 1 and variable 2
Titles are VERY important. Title your axis, the
integers and give the graph a title.
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Data Analysis

• Descriptive Statistics
• Summary of data to illustrate patterns and
  relationships BUT cant infer conclusions
• Inferential Statistics
• Statistical tests that allow us to make
  conclusions in relation to our hypothesis.
• eg. Mann-Whitney or Spearmans Rho.

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Independent Dependent Variables
Confounding Extraneous Variables
Cause Effect
Experimental Methods
Types of Experiments Laboratory Field Quasi
(natural)
Independent Measures Repeated Measures Matched-P
airs

Sampling Methods Opportunity Random Snowball Strat
ified Self-Selected
Ethics
Ecological Validity Reliability Validity