Chapter 11

Question 1

How do researchers design studies to prevent internal validity threats?

Answer 1

The 6 threats to one-group, pretest/posttest designs can be ruled out if an experimenter conducts the study using a comparison group (either a posttest-only design or a pretest/
posttest design).

Question 2

How do you interrogate an experiment with a null result to decide whether the study design obscured an effect or if there is truly no relationship?

Answer 2

Obscuring factors can be sorted into two categories:
1. Not enough between-groups difference (from weak manipulations, insensitive measures, ceiling or floor effects, or a design confound acting in reverse.)
2. Too much within-groups variance (from measurement error, irrelevant indi-
vidual differences, or situation noise.)
Too much in-group variance can be counteracted by using multiple measurements, more precise measurements, within-groups designs, large samples, and very controlled experimental
environments.

Question 3

What are the 6 threats to internal validity that are especially relevant to the one-group, pretest/posttest design?

Answer 3

1. Maturation - where there is a change in behaviour that emerges spontaneously over time > can be mitigated via comparison group
2. History - results from a historical or external factor that systematically affects most members of the treatment group at the same time as treatment itself > a comparison group could help
3. Regression - when a group average is unusually extreme at time 1, the next time that group is measured is likely to be less extreme > comparison group
4. Attrition - when a certain kind of participant drops out a lot (systematic) > remove participant data
5. Testing - a specific kind of order effect, refers to a change in the participants as a result of taking a test more than once > using only posttest design
6. Instrumentation - occurs when a measuring instrument changes over time > calibrate instruments and counterbalancing

Question 4

What are the 3 potential internal validity threats to any experiment?

Answer 4

1. Observer bias - occurs when researchers’ expectations influence their interpretation of the results
2. Demand characteristics - when participants guess what the study is supposed to be about and change their behavior in the expected direction
3. Placebo effects - occurs when people recieve a treatment and really improve but only because the recipients believe they are recieveing a valid treatment

Question 5

What is the really bad experiment?

Answer 5

The one-group, pretest/posttest design is like a pretest/posttest design has no comparison groups

Question 6

What are the supgroups of selection threats?

Answer 6

1. Selection-history threat - an outside event or factor effects only those at one level of the independent variable
2. Selection-attrition threat - only one of the experimental groups experiences attrition