Midterm 1 - Lecture 4 (Ch8)

Question 1

Random Assignment of people to condition (Experimental Design)

Answer 1

• Balances influence of random effects across the conditions
• Especially as sample size increases

Question 2

What are the potential Experimental Design options (3)

Answer 2

• Independent Groups
• Repeated Measures
• Matched Pairs

Question 3

Independent Groups - Between Groups (Experimental Designs Options)

Answer 3

Between-subjects design: in which different people experience the levels of the independent variable

• The experimental and control groups are distributed between different people

Question 4

3 broad steps to designing a between-subjects design:

Answer 4

• Obtaining two approximately equivalent groups of participants
• Introducing different levels of the IV to the participants
• Measuring the IV

Question 5

First step to planning a between subjects design is…

Answer 5

To decide how to assign participants to the levels of the IV

• Must create equivalent groups and eliminate any potential selection differences: the people selected to be in experimental condition should not differ in any systemic way from those selected to for the control condition
• Prevented through random assignment

Question 6

Second step (to any experiment, really) is to…

Answer 6

Operationalize the IV, creating at least 2 levels

• This can look like an exp. group that receives treatment, and a control that doesn’t

Question 7

Third step to planning a between-subjects design:

Answer 7

• Third step: planning an experiment to operationalize the depended variable, which will allow us to measure the effect of the IV on the DV
• Same measurement procedure is used for both conditions, so that they can be compared

Question 8

When the results can be confidently attributed to the IV, the experiment is said to have…

Answer 8

high internal validity

Question 9

If the scores of the dependent variable differ between groups, researchers can conclude that…

Answer 9

the independent variable is based on the logic that if the only difference between the groups is the manipulated independent variable, then this difference must be the cause of any difference in the measured depended variable

Question 10

In random assignment for Between-Subjects, participant characteristics cannot be…

Answer 10

an alternative explanation to an experiment’s results

Question 11

Repeated Measures - Within Groups (Experimental Designs Options)

Answer 11

In which all the same people experience all levels of the IV

-All participants experience all conditions; ensures that the groups for each condition are absolutely identical
- Removes all possibility of selection bias

Question 12

Benefits of Repeated Measures:

Answer 12

□ Need fewer participants (because everyone participates in all conditions)
□ Less cost (in times when participants are scarce - can also maximize data collection)
□ More power to see the effect of IV on DV if there is one (When the exact same people are in both conditions; By accounting for individual differences in a within-subjects design, we are better able to detect an effect of the IV on the dependent variable, if one exists)

Question 13

Problems with Repeated Measures Designs:

Answer 13

□ “Mortality”
□ Length of time interval
□ Dealing with counterbalancing orders
□ Order effects

Question 14

Carry-Over Effects/Order Effects (Repeated Measures)

Answer 14

Whenever a participant’s response in a given condition is affected by having previously participated in other conditions in that experiment.

Question 15

3 types of order effects:

Answer 15

◊ Practice effects
◊ Fatigue effects
◊ Contrast effects

Question 16

How can we address order effects?

Answer 16

• Filler tasks (for contrast effects); meditating
• Passage of time (for fatigue & contrast effects); Can be minutes, hours, days, weeks…

Question 17

How can we deal with counterbalancing orders?

Answer 17

Balanced Latin Squares:

1. Each treatment must occur once with each participant
2. Each treatment must occur the same number of times for each period or trial
3. Each treatment must precede and follow every other treatment an equal number of times

Question 18

Pretest-Posttest Design:

Answer 18

Pretest-posttest design: an experimental design in which the dependent variable is measured both before and after manipulation of the independent variable

• To ensure equivalent random assignments, researchers can choose to add a pretest to measure that variable before any experimental manipulation
• Scores are then compared to ensure before any experimental manipulation

Question 19

3 Advantages of a Pretest-Posttest Design

Answer 19

• To counter problems associated with a small sample size
• To select appropriate participants
• When participants might drop out of the study

Question 20

“To counter problems associated with a small sample size” (Pretest-Posttest Design)

Answer 20

Although RA is likely to produce equivalent groups, as sample size decreases, it becomes less likely that the groups will be approximately equal

Thus, a pretest enables the researcher to asses whether the groups were already roughly equivalent on some critical variable before the manipulation began

Question 21

“To select appropriate participants”(Pretest-Posttest Design)

Answer 21

A researcher might use a pretest to find the lowest/highest scorers on a measure of smoking, math anxiety, etc.

Once targets are identified, they’re randomly assigned to the experimental or control group
However, this method may introduce another issue: regression toward the mean

Question 22

“When participants might drop out of the study” (Pretest-Posttest Design)

Answer 22

To ensure that those who remain do not differ across conditions
Participants choosing to leave a study can produce a problem known as selective attrition, with dropouts rates from long-term studies

If people are dropping out for some reason related to the manipulation, this selective attrition may cause a difference between groups

Can become an alternative explanation for results

Thus, pretests can enable researchers to examine whether selective attrition is a plausible alternative

Question 23

Disadvantage of Pre-test/Post-test Design

Answer 23

Can sensitize participants to what you’re studying, enabling them to figure out your hypothesis

May react differently to the manipulation than they would have without the pretest

Difficult to generalize these results to people who have not received a pretest

Question 24

How can we prevent sensitizing participants to what you’re studying?

Answer 24

How can we prevent this?
Pretests can be disguised using deception
Embed the pretest in a set of irrelevant measures, so that it’s not obvious that the researcher is interested in a particular topic
® Examine the influence of a pretest directly, by including the presence or absence of a pretest as another condition, embedding the levels of the IV within those two groups

Question 25

Matched Pairs Design:

Answer 25

Matches people on a crucial participant characteristic (EX: pairs of people with similar age, need for control, typing speed, etc.)

One member assigned control group, other member assigned experimental

Can be either the DV itself or another variable

Question 26

When are matched pairs designs most likely to be used?

Answer 26

When not possible to obtain a large sample size, making RA less likely to be successful in created equivalent groups

Large numbers can be too pricey