Ch. 10 Quasi-Experimental Designs and Program Evaluation

Question 1

characteristics of true experiments

Answer 1

• manipulate an IV
• treatment, control conditions
• high degree of control, esp random assignment to conditions
• unambiguous outcome regarding effect of IV on DV (internal validity)

Question 2

advantage of true experiments

Answer 2

threats to internal validity are controlled
- confoundings are controlled
- tule out alternative explanations to make a casual inference about effect of IV on DV

Question 3

8 general classes of threats to internal validity

Answer 3

history, maturation, testing, instrumentation, regression, selection, subject attrition, additive effects with selection

Question 4

history

Answer 4

when an event occurs at the same time as the treatment and changes participants’ behavior. participants “history” includes events other than treatment. difficult to distinguish whether treatment has an effect

Question 5

maturation

Answer 5

participants naturally change over time. there maturational changes, not treatment, may explain any changes in participants during an experiment

Question 6

testing

Answer 6

taking a test generally affects subsequent testing. participants’ performance on a measure at the end of a study may differ from an initial testing because of their familiarity with the measures

Question 7

instrumentation

Answer 7

instruments used to measure participants’ performance may change over time. changes in participants’ performance may be due to changes in instruments used to measure performance, not to a treatment

Question 8

regression

Answer 8

participants sometime perform very well or very poorly on a measure because of chance factors (e.g., luck). there factors are not likely to be present during a second testing, so their scores will not be so extreme. the scores will “regress” (go toward) the mean. regression effects, not treatment, may account for changes in participants’ performance over time.
a test score = true score + error

Question 9

subject attrition

Answer 9

when participants are lost from the study (attrition), the group equivalence formed at the start of the study may be destroyed. differences between treatment and control groups at the end of the study may be due to differences in those who remain in each group

Question 10

selection

Answer 10

occurs when differences exist between individuals in treatment and control groups at the start of a study. these differences become alternative explanations any differences observed at the end of the study.

Question 11

threats to internal validity that even true experiments may not eliminate

Answer 11

contamination, experimenter expectancy effects, novelty effects

Question 12

contamination

Answer 12

occurs when there is communication about the experiment between groups of participants.
three possible outcomes
- resentment
- rivalry
- diffusion of treatments

Question 13

expectancy effects

Answer 13

occur when an experimenter unintentionally influences the results of an experiment.
two types
- expectations lead to systematic errors in interpretation of participants’ performance
- expectations lead to errors on recording data

Question 14

novelty effects

Answer 14

refer to changes in people’s behaviors simply because an innovation produces excitement, energy, enthusiasm