Experimental Designs: Between and Within Subjects Design: Chapter 8 & 9 Flashcards

1
Q

between groups

A
  • 2+ groups are formed at random from a
    pool of subjects
  • each group receives a different experimental treatment (value of the IV)
  • scores for the groups are
    compared
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2
Q

between groups: obtaining results

A
  • 1 score per individual
  • these are independent measures
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3
Q

do scores vary within groups

A

yes

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4
Q

systematic variance

A

difference in the DV

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5
Q

looking for an effect of IV

A

to look for an effect of IV, compare mean scores (DV) for each group

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6
Q

determining statistical significance

A

compare between groups variance to within groups variance
F = between-group variance / within group variance

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7
Q

When there is a large within-group variance, it is
difficult to see an effect, we want to ____

A

minimize it

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8
Q

large versus small variance in groups

A
  • large variance in between groups (BG) = good
  • large variance in within groups (WG) = bad
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9
Q

keeping within group variance low

A

limit individual differences
- Standardizing procedures
- Holding a participant variable constant
- Increase sample size

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10
Q

individual differences in between-groups are usually ____

A

always a potential confounding variable for this design

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11
Q

making between groups as equal as possible

A
  • created equally
  • treated equally, except for IV
  • composed of equivalent individuals
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12
Q

randomization

A
  • participants randomly assigned to groups to
    ensure groups are as equal as possible before
    treatment or intervention
  • most powerful technique to control for the effect
    of pre-existing differences
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13
Q

randomization vs random sampling

A

randomization:
- random assignment of Ss to experimental
or control groups in a particular study
random sampling:
- random selection of Ss from a larger
population to participate in a study

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14
Q

free random assignment

A
  • groups are based on chance
  • if 2 groups +, table of random numbers is used to guard against repetition
  • should lead to equality, but no guarantee
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15
Q

randomization: matched group

A
  • participants matched on critical variables that may act as important confounds
  • inherent in within-groups designs.
  • ex:
    1. intelligence
    2. gender
    3. age
    4. severity of illness
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16
Q

randomization: randomized blocks

A

groups of individuals are matched in blocks

17
Q

matched groups

A

critical variables that can act as confounds
- intelligence
- gender
- age
- severity of illness

18
Q

matching procedure

A
  1. Rank subjects on the variable for which
    control is desired. May require pretest.
  2. Segregate subjects into matched pairs
    on that variable.
  3. Randomly assign pair-members to the
    conditions.
19
Q

advantages of between-groups

A
  • very simple design
  • no carryover effects
20
Q

disadvantages of between-groups

A
  • requires many participants
  • individual differences & environmental differences
  • groups must be equivalent before the manipulation
21
Q

within-groups design

A
  • only one treatment group and each subject is
    given all levels (or conditions) of the IV
  • comparison = between scores obtained at
    different levels of the IV for same participants
  • each participant serves as their own control
22
Q

categories of within-groups

A
  • concurrent measures
  • repeated measures
23
Q

concurrent measures

A
  • all levels of IV are present at the same time – choice paradigm
  • subjects choose the value of the IV they prefer
24
Q

Harlow: monkeys cloth mother
(comfort) versus wire mother
(food).
Measured time spent at
each mother.
This is an example of ______

A

concurrent measures

25
repeated measures
- most common approach for within-subjects - every subject receives all values of the IV - participant's performance is the basis of comparison
26
what does the repeated measures accomplish
1. equating groups (by using same participants) 2. reducing within-group variance (by controlling for individual differences)
27
advantages of repeated measures
- increases sensitivity - increases ability to detect a treatment effect - error variance is reduced considerably because the participants become their own control (individual differences are eliminated)
28
main issue with repeated measures: carryover effects
- effects that one treatment may have on another treatment - includes: practice effects, fatigue, boredom, interference - exposure to one manipulation may produce consequences influencing response to manipulations
29
solutions to carryover effects
- randomization - counterbalancing
30
counterbalancing
- all possible treatment orders are used equally - equal numbers of participants in each treatment condition
31
counterbalancing: examples
2 treatments - 2 x 1 3 treatments - 3 x 2 x 1 4 treatments - 4 x 3 x 2 x 1 product is the total amount of combinations
32
latin square design
- each treatment (A, B, C & D) occurs equally often in each position in the experiment - refer to chapter 8&9, slide 32
33
reversibility in within-groups
- within-subjects designs = not adequate IF experimental conditions produce lasting effect on the participant (cannot be reversed). - IVs permanently alter the development or state of participants - have irreversible carry-over effects
34
examples of irreversible carryover effects
- physiological damage (brain lesions) - interventions that improve or worsen a skill, such as learning or memory - habituation
35
reversal design: ABA design
- allows verifying the presence/absence of carry-over effects Condition A = measure behavior at baseline Condition B = measure during intervention Condition A = measure after intervention stopped
36
Does behaviour return to the baseline?
YES: no carryover effect NO: carryover effect
37
carryover effect desirability
- carryover effect can be desirable
38
advantages of within groups
- fewer participants required - greater sensitivity to treatment effect (elimination individual differences) - good when participants are hard to find - each participant acts as his own control - powerful design under suitable conditions
39
disadvantages of within groups
- not suitable when carryover effects are permanent - participant attrition may be a problem