Lecture 14: The Experimental Research Design l

Question 1

what is the most powerful research method and why?

Answer 1

the experimental method because it contains high constraints on variables

Question 2

goals of the experimental strategy

Answer 2

• to arrive at a causal explanation
• to provide a comparison of situations (conditions) in which the proposed cause is present or absent

Question 3

the experimental research design

Answer 3

Manipulation of one variable (IV) to demonstrate its effect on another variable (DV) while holding other potential influences constant

Question 4

how does the experimental strategy establish causality?

Answer 4

strict control; creating an unnatural situation where variables are isolated from the influence of other variables

Question 5

what designs can establish causality?

Answer 5

experimental and quasi-experimental

Question 6

is it possible to prove causality?

Answer 6

no, it is only possible to show its likelihood (alpha value associated with statistical test)

Question 7

2 steps to establishing a cause-and-effect relationship

Answer 7

1. Establish that the effect happens after the cause occurs
2. Establish that one specific variable (IV) is responsible for changes in another variable (DV)

Question 8

4 factors that one must establish to establish that two variables are causally related

Answer 8

• time order
• co-variation
• rationale/explanation
• non-spuriousness

Question 9

time order

Answer 9

the cause x must have occurred before the effect y

Question 10

example of time order

Answer 10

individuals arrested for domestic assaults tend to commit fewer subsequent assaults than similar individuals who are accused in the same circumstances but are not arrested

Question 11

co-variation

Answer 11

changes in the value of x must be accompanied by changes in the value of y

Question 12

example of co-variation

Answer 12

the more years of schooling, the higher the projected income

Question 13

rationale/explanation

Answer 13

there must be a logical and compelling explanation for why these two variables are related

Question 14

example of rationale/explanation

Answer 14

the relationship between childhood poverty and petty theft

Question 15

non-spuriousness

Answer 15

it must be established that x and only x have caused the observed changes in y; alternative explanations must be ruled out

Question 16

example of non-spuriousness

Answer 16

grade schools with larger libraries cause or produce students who are better readers (possible third variable = parents’ education)

Question 17

two types of experimental designs

Answer 17

Between-groups design
Within-groups design

Question 18

between-groups design

Answer 18

• Two or more samples (groups) are formed at random from a pool of subjects
• Each group is composed of different participants
• Each group is assigned to a different condition (value of the IV) and the values of each group are compared

Question 19

experimental group

Answer 19

the participants in your experiment are exposed to an experimental manipulation

Question 20

control group

Answer 20

a group in your experiment that is not exposed to the manipulation and that is used for comparison purposes

Question 21

placebo control group

Answer 21

the group receives a placebo treatment with no real treatment

Question 22

placebo effect

Answer 22

just believing that the treatment will have an effect can cause a response

Question 23

effect of treatment/ placebo comparisons

Answer 23

they indicate the effect on DV beyond placebo effects

Question 24

waitlist group

Answer 24

participants who sign up to receive the same treatment

Question 25

strength of waitlist groups

Answer 25

it controls for motivation across groups

Question 26

limitation of waitlist groups

Answer 26

comes at a cost: the experimenter must offer the treatment eventually

Question 27

within-groups design

Answer 27

• Only one sample (group) is formed and each person participates in all conditions (levels of the IV)
• Values are compared across conditions within each participant (values from the same participant in different conditions)

Question 28

independent vairable

Answer 28

• The variable we think is the cause
• The manipulated variable in experimental studies
• Is manipulated by creating a set of treatment conditions

Question 29

dependent variable

Answer 29

• The variable we think is the effect
• Results from the manipulation of the IV (cause)
• The outcome (what is measured in each of the conditions)

Question 30

extraneous variables

Answer 30

• Any other variable in the study
• They do not matter if they do not affect the outcome and do not correlate with the manipulated variable
• Ex. age, gender, personality, etc.

Question 31

4 basic elements of the experimental research strategy

Answer 31

1. manipulation
2. measurement
3. comparsion
4. control

Question 32

manipulation

Answer 32

The researcher manipulates one variable by changing its value to create conditions

Question 33

measurement

Answer 33

a second variable is measured for each condition, resulting in a set of scores in each treatment condition

Question 34

comparison

Answer 34

the scores in each condition are compared with the scores in other conditions

Question 35

control

Answer 35

all other variables are controlled to be sure they do not influence the variables being examined

Question 36

what elements of the experimental research strategy are unique to this strategy?

Answer 36

manipulation & control

Question 37

steps of manipulation

Answer 37

• First, decide on the levels of the IV you would like to examine
• Manipulate one variable and observe the second variable: is it affected by this manipulation?

Question 38

purpose of manipulation

Answer 38

to determine the direction of the effect

Question 39

what does a finding of causality assume?

Answer 39

that the researcher has controlled all other vairables

Question 40

manipulation of outside variables

Answer 40

Manipulation can also be used to control the influence of outside variables

Question 41

active manipulation

Answer 41

Active manipulation of the IV allows us to ensure that the IV is not changing along with another variable that can account for the relationship you are interested in

Question 42

when can you be confident that changes in the IV are not caused by an outside variable?

Answer 42

if the third variables are controlled

Question 43

control

Answer 43

• Must make sure that there are no other factors contributing to the changes observed in the DV beyond that of the IV
• Must rule out all other possible explanations for changes in the DV (eliminating confounding variables that can influence the IV & DV)

Question 44

confounding variables

Answer 44

• A special class of extraneous variables that changes systematically with an IV and can influence the DV
• Therefore, they can mask the true effect of the IV
• They matter because they vary systematically along with the IV and can affect the outcome
• When the IV and confounding variables change together systematically, we cannot conclude cause and effect relationships between the IV & DV
• Provide alternative explanations of the results

Question 45

extraneous vs. confounding variables memory example

Answer 45

• You are conducting a memory experiment and there is noise due to construction around the lab
• Noise would be an extraneous variable if it affects all conditions
• If only one condition is affected and there is reason to believe noise will impact memory, it is a confounding variable because the effect of the noise on memory becomes confused with the effect of the IV on memory

Question 46

confounding variables and internal validity

Answer 46

• Confounding variables are an important threat to internal validity: we don’t know if it’s the IV or the confounding variable that is causing the change in the DV
• The presence of confounding variables offers an alternative explanation for your results
• It introduces ambiguity

Question 47

Schmidt memory study and confounding variables

Answer 47

Schmidt 1994 examined the effects of humour on memory but the beneficial effects of humour on memory were due to surprise

Question 48

what makes extraneous variables become confounding variables?

Answer 48

• The variable must affect the DV
• The variable must vary systematically with the IV

Question 49

how do we deal with confounding variables?

Answer 49

Examine extraneous variables for possible influences on the DV

Question 50

three categories of extraneous variables

Answer 50

Environmental variables
Partcipants variables
Time-related variables

Question 51

importance of control

Answer 51

We need to introduce experimental control so that extraneous variables do not become confounding variables

Question 52

5 ways to control for possible confounding variables

Answer 52

Remove them
Hold them constant
Use a placebo control
Match them across conditions
Randomize them