Components of a causal relationship

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Components of a causal relationship

• Does a change in X cause a change in Y?
• There are 3 components
• 1) Co-variation of events
• 2) Time-order relationship
• 3) Elimination of alternative causes.

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Independent Variable

• The presumed "cause" of a behavioral effect or
  change
• Manipulated (varied) by experimenter
• IV has several levels selected by experimenter
• Occurs, or can be "set up" before DV is measured
• "Independent" of what the subject does.

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Dependent Variable

• Some measure of behavior that is a measure of the
  effect of the IV(cause)
• What is recorded by the experimenter
• The behavior occurs after IV is varied, and DV
  measures the behavior
• "Depends" on manipulation of the IV
• DV does not have levels.

4
Confounding Variable

• Any variable that is a potential cause for the
  experimental effect, other than the IV
• Any variable whose values change systematically
  across levels of the IV.

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Control variable

• Variable whose values remain the same across
  levels of the IV (eg, room temp, light levels,
  time-of-day, etc).

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Random variable

• Variable whose values vary randomly in an
  unbiased way across levels of the IV
• Random variables are usually created by the
  process of random assignment.

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Subject variable

• A personal characteristic (eg, height, weight,
  gender, ethnicity, socio-economic status, etc).

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Control group

• The group that receives zero or the absence
  of the IV
• Eg, the placebo group in a drug experiment
• The group that serves as a baseline to compare
  with the performances of the experimental groups.

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Experimental groups

• The groups that receive non-zero values of the IV
• Eg, the drug groups in a drug study
• The performances of these groups are compared
  with the performance of the control group.

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Conceptual Definition

• Definition of a variable at the conceptual or
  idea level
• Tends not to be very precise
• Tends to be more general, more vague.

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Operational Definition

• Specifies the operations or procedures necessary
  to measure the variable
• Very precise
• Not general or vague at all
• Tells how the variable was measured
• There may be many ODs for a single CD.

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ODs and CDs - Example 1

• Conceptual - Amount of alcohol
• Operational - of beers in 1 hour (0,1,2,3)
• Operational - grams of alc./kg body weight
• Operational - BAC (mg alc./deciliter blood).

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ODs and CDs - Example 2

• Conceptual - Helping behavior
• Operational - of people who help a victim
• Operational - duration of helping behavior
• Operational - seconds before helping occurs
  (latency).

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EXR-intermediate scenarios
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Complex designs

• More than one IV
• Eg, Left/Right and 1, 5, or 10 spaces fr. center
• More efficient than single IV experiments
• Gives more information
• Allows analysis of main effects and interactions.

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Complex designs - terminology

• An IV is called a factor
• number of numbers how many IVs there are
• values of numbers how many levels each IV has
• 2 X 2 design (two IVs, each with 2 levels)
• 2 X 3 design (first IV has 2 levels, second IV
  has 3 levels)
• 2 X 8 design (first IV has 2 levels, second IV
  has 8 levels)
• 2 X 2 X 4 design (first IV has 2 levels, second
  IV has 2 levels, third IV has 4 levels).

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Main effects

• There is one potential main effect for each IV
• A 2 X 8 design has two possible main effects
• A 2 X 2 X 4 has three possible main effects
• A main effect is present if an IV had a
  significant effect on the experiments outcome
  (regardless of the effects of the other IVs).

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Interactions

• Please memorize An interaction occurs if the
  effect of one IV varies depending on the level of
  the other IV

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EXR-horn honks and abstracts
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Designing experiments

• Two general types of designs
• Between-subjects (between groups or independent
  groups) each group gets one level of the IV 
• Within-subjects (within-group or repeated
  measures) each subject gets all levels of the
  IV
• Equivalency of groups at each level is built-in
  for within-subjects and achieved by random
  assignment for between-subjects
• Within - more efficient in terms of of subjects
• Within - zero variability (ind diff) between
  levels.

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Order effects

• Order effects (practice effects) experiencing
  one level affects behavior in another level
• Eg, does content (biology text vs. novel) affect
  proofreading speed? Order is Biology-Novel
• Eg, practice, boredom, fatigue
• Order effects cannot occur in between-subjects
  and are controlled in within-subjects by
  randomization or counterbalancing.

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Differential carryover effects

• (carryover effects, differential/asymmetrical
  transfer effects)
• The effect of the first level on the second level
  differs depending on which comes first
• Effect of B following A ? effect of A following B
• Confound is due to which level precedes which.

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FIG Order effects in proofreading
(no practice)
(practice)
Group 1
Biology
Novel
1
2
(no practice)
(practice)
Group 2
Biology
Novel
1
2
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FIG Differential carryover effects in problem
solving
(no practice)
(practice)
Group 1
Neutral instructions
Special instructions
1
2
(no practice)
(practice)
Group 2
Neutral instructions
Special instructions
1
2
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Other considerations

• Mixed designs (some between, some within)
• Small-n designs
• Matched groups designs
• Demand characteristics cues that tell subjects
  how they should behave (eg, drug studies)
• Blind and double-blind procedures
• Internal and external validity
• Quasi experiments.

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