Experimental Methods

Question 1

structure of an experiment

Answer 1

1. manipulating the IV
2. randomly assign to conditions

Treatment A Treatment B

2.5 control/eliminate extraneous variables
3. measure DV from given scores
4. compare

Question 2

extraneous variables

Answer 2

any variable that has some relationship to the DV but is not an IV or DV

example:
- couples
- IV: manipulating stress levels in one partner
- DV: measure how the other partner comfort them socially
- extraneous variable: how long they’ve been together affects how well they can comfort their partner
gender also affects how well they can comfort their partner

Question 3

confound

Answer 3

alternative explanation for relationships between IV and DV

Question 4

design confound

Answer 4

mistake in the design of the IV, such that the second variable
- systematically with the IV
- example:
study:

Question 5

selection effects

Answer 5

participants in one level of the IV are systematically different from those in the other
- example:
assigning people to eat a big bowl of pasta for breakfast
note: not many people eat pasta for brekkie/there might have been experimenters who offered more pasta
systematic differences
- men might choose bigger than women
- people might have come in hungry or not

Question 6

what is the difference between extraneous variables and confounds?

Answer 6

extraneous variables are any variable in the context of the study that has some relationship to DV but is not IV or DV
varies randomly

confounds: varying systematically with levels of IV
varies systematically

Question 7

ways to avoid selection effects

Answer 7

• random assignment
• matched groups

Question 8

random sampling

Answer 8

everyone has a chance of being selected

Question 9

matched groups

Answer 9

participants are assigned by variables that match each other
structure:
group 1 group 2
similar characteristic 1
similar characteristic 2
similar characteristic 3

Question 10

between subjects design

Answer 10

different groups of participants only see ONE condition or the other
- cons: there are less people in each group because its split into two

Question 11

within subjects

Answer 11

one group of participants completes all conditions
- compares scores from the same person

Question 12

posttest-only design (between subjects)

Answer 12

participants are randomly assigned to a condition and tested on the dependent variable once
- preferable when pretesting would affect results
example:
experimenting on how a new study program affects children’s intelligence
posttest-only design: giving them a test afterwards to see the results

Question 13

pretest-posttest design (between subjects)

Answer 13

participants were randomly assigned to a condition and tested on DV twice: before and after exposure to IV
- preferable when ensuring groups were equivalent at the start
- preference when showing improvement over time

Question 14

advantages of within subjects designs

Answer 14

• participants in the two groups will be equivalent
  -requires fewer participants than between subjects

Question 15

disadvantages of within subjects

Answer 15

• order effects
• may not be possible
• participants may figure out what the experiment is about
  -> leading to demand characteristics

Question 16

order effects

Answer 16

exposure to one level of the IV influences responses to the next level
- practice effects: participants get better or worse with fatigue
- carryover effects: come contamination carries over from one condition to the next

avoid by counterbalancing by changing the order for participants
example: have some people run without pepsi or with pepsi first

Question 17

demand characteristics

Answer 17

cues that lead participants to guess experiment’s hypothesis

Question 18

sources of confounds

Answer 18

• environment
• individual differences
• time

Question 19

environment as a source of confound

Answer 19

setting or context differs across treatment conditions -> design confound
- control by holding everything except IV constant across conditions

example:
study about effects of stress in crowded rooms
- the crowded condition accidentally studied how room temp affects stress

Question 20

individual differences as a source of confound

Answer 20

• assignment to conditions result in groups with different characteristics -> selection effects
• people are different (knowledge, mindset, experiences
• control with random assignment

Question 21

time as a source of confound

Answer 21

• treatment conditions occur at different times and experience over time causes change in the DV
• often avoided with between subjects design
• if within subjects -> counterbalance

Question 22

maturation

Answer 22

time related confound
- subjects naturally change physiologically or psychologically between treatment conditions

use comparison/control groups to control for changes in maturation

Question 23

history

Answer 23

time related confound
- an outside event occurs between treatment conditions and affects the DV in conditions subsequent to event

use comparison/control groups

Question 24

regression to the mean

Answer 24

time related confound
- extreme scores in first treatment condition statistically likely to become less extreme in subsequent conditions

Question 25

attrition

Answer 25

time related confound
- subjects drop out of the study before completing all conditions

• remove participants who dropped out from pretest average too
• analyze pretest scores to see if people who dropped out were significantly different from those who didn’t

Question 26

instrumentation

Answer 26

time related confound
- chnage in measurement instruments between treatment conditions affects measurement of DV subsequent to instrument change

• used fixed tests; control group

Question 27

threats to internal validity

Answer 27

• observer bias
  researchers expectations influence results (tendency to see what we expect to see)
• demand characteristics
• placebo effects
  use active control group

Question 28

observer bias

Answer 28

masking: concealing which condition participant has been assigned to

double masked: neither participants nor researchers know what condition they are in