Between group designs 5.1

Question 1

Between subjects (groups) design

Answer 1

• Each ppt participates in only one level of the IV (or subject variable)
• Ppts from the different groups are compared to each other

Question 2

Within subjects (groups) design

Answer 2

• Each ppt participates in each level of the IV

* Participants are compared to themselves

Question 3

Mixed Factorial design

Answer 3

• A design that includes more than one IV (factor)
• At least one IV (factor) is manipulated between subjects
• At least one IV (factor) is manipulated within subjects

Question 4

Between group experiments

Answer 4

• Equivalent groups
• Comparable treatment of groups
• IV is manipulated by researcher and a DV is measured
• Causal inferences warranted (if internally valid)

Question 5

Between groups quasi-experiments

Answer 5

• Non-equivalent groups
• Comparable treatment of groups (if possible)
• Subject variable is determined by researcher and DV is measured
• Causality questionable even in the best/most controlled designs

Question 6

What do experiments test?

Answer 6

• causal realtionships
  •The IV is manipulated by the researcher
  •Equivalent groups of ppts are compared
  •Internally valid
  •It is the IV (not something else) that caused the change in the DV
  •It will have extraneous variables
  •It should be free of confounds and confounding variables

Question 7

Extraneous variables vs. confounding variables

Answer 7

Ex:
•Intelligence is an extraneous variable
•It is a confound if the smarter people are in one condition and the less smart people are
in the other

Question 8

Between groups advantages

Answer 8

• Reduced demand characteristics
• Harder to guess what the experiment is about (which can influence behavior)
• Experiments take less time per ppt

Question 9

Between group disadvantages

Answer 9

•Are less statistically powerful than within-group designs
•More error because people are not compared to themselves
•Use different statistical tests that account for this
Test Stat. = (Effect of IV +error variance) /error variance
•May be more likely to have experimenter effect confounds

Question 10

Creating equivalent groups in between group designs

Answer 10

•Make sure individual differences are just extraneous variables and not
confounds
•Random assignment
•Don’t confuse with random selection of participants!

Question 11

Matching

Answer 11

True-experiments:

1) Match participants with extraneous variables of concern
2) Randomly assign them to groups

Matching in quasi experiments that compare subject variables:
•Match ppts so that the groups are as similar as possible aside from the
subject variables

Question 12

Selection Bias

Answer 12

• a confound
  •Don’t let ppts pick which group they are in.
  •The groups will not be equal.
  •Characteristics that influence their choice will co-vary with the levels of the IV

Question 13

Participant Biases

Answer 13

Demand characteristics
•Design features that make it 
obvious what a study is about
•They are less apparent in 
between-group manipulations
•“Good” participant

Evaluation apprehension (anxiety)
•Similar in between- and within-
group designs

Question 14

Dealing with demand characteristics

Answer 14

•Deception 
•Placebos
•Filler trials
•Single- and double-blind research
•Ask what they thought the experiment 
was about after it is over

Question 15

Experiment Biases and Experimenter effects

Answer 15

•The experimenter 
behaves in ways that 
bias the results
•biased measurements
•influencing ppts
behaviors

Question 16

Comparable treatment of groups

Answer 16

Minimally different stimuli
•The conditions should differ only on the
constructs associated with the levels of the IV
•If extraneous variables in the stimuli co-vary with
the manipulation, this is also a confound