CHAPTER 13 Quasi Experiments

Question 1

True experiment - 3 conditions:

Answer 1

1. the groups assigned to different treatment conditions must be initially equivalent, which is usually accomplished by random assignment of subjects;
2. the independent variable must be a manipulated variable; and
3. the existence of a control condition against which the behaviour of experimental subjects (as in between-subject designs) or of the same subjects in the treatment condition (as in within-subject designs) is compared.

Question 2

quasi experiment:

Answer 2

quasi experiment: research procedure in which the scientist must select subjects for different conditions from pre-existing groups

Where one or more of these conditions are not satisfied but the purpose of the research is to imply a causal connection between the independent variable and a subsequent behaviour, we have a quasi-experiment

Question 3

How are quasi experiments different from true experiments?

Answer 3

• A quasi experiment, by contrast, does not permit the experimenter to control the assignment of subjects to conditions.
• in a quasi experiment it is necessary to select subjects for the different conditions from previously existing groups
• The independent variable in a quasi experiment is often called a subject variable if it is a characteristic of the subjects on which they have been selected, such as sex of participants

Question 4

Under what circumstances can quasi experiments be a useful tool?

Answer 4

1. it may be the only possible way to study the impact of a natural event, for example, how residents cope after a flood
2. external validity of a quasi experiment may be higher than that of a true experiment done on the same problem if the quasi experiment studies subjects or settings that are more appropriate to the question of interest than a true experiment could do.
3. For example, if you wanted to know the effects of changing the size of work groups in a widget factory on productivity, an experiment using college students working at solving anagrams would probably not apply. It would have little external validity.
4. Quasi-experimental research allows the examination of natural experiments, which are formed when real-world events divide people into two groups for comparison

Question 5

What is the major weakness of quasi experiments?

Answer 5

• Less control, not knowing if the variable which is not controllable is confounding the results

Question 6

nonequivalent control group design:

Answer 6

research design having both an experimental and a control group wherein subjects are not randomly assigned to groups

• this is the most typical of quasi design
• problem with this design is in determining how to compare results between the experimental and control groups when the two groups were not equivalent to begin with

Question 7

Under what circumstances are the results of quasi-experiments that use this design interpretable?

Answer 7

• (1) if the behaviour of both groups are the same on the pretest and the experimental group’s behaviour has changed on the posttest while the control group’s has not, or
• (2) if there is a crossover between the experimental group and the control group on the pretest and on the posttest (i.e., the experimental group has a lower measure than the control group on the pretest but a higher measure on the posttest).

Question 8

interrupted time-series design:

Answer 8

research design that allows the same group to be compared over time by considering the trend of the data before and after experimental manipulation

1. a series of pretest measurements over time,
2. the occurrence of the significant event (treatment or intervention), : in the case of media/suicide rates, they changed the laws in Austria to limit the amount of media coverage to avoid copy cat suicides, so that is the intervention and is what differentiates itself from merely observational study
3. a series of posttest measurements.

Question 9

Under what circumstances is interrupted time-series design useful?

Answer 9

• used by industries, schools, government programs, and human service organizations for monitoring program functioning.

Question 10

Problems with data interpretation, in interrupted time-series design:

Answer 10

• (1) the treatment or intervention is gradual rather than abrupt, (2) there is a delay impact of the intervention,
• (3) the time series is short, and
• (4) there are incomplete or inaccurate archival data

Question 11

summative evaluation

Answer 11

is to assess whether a given program is functioning adequately. Its outcome is used to determine whether a program should be cut back, discontinued, maintained, or expanded

Question 12

formative evaluation

Answer 12

is to recommend changes that will improve program functioning

Question 13

repeated-treatment design:

Answer 13

design in which a treatment is withdrawn and then presented a second time

• attempt to improve the validity of the experiment
• The treatment must be one that can be withdrawn without causing complications in the analysis of data

Question 14

What are the common quasi-experimental designs used in developmental psychology? What are their relative advantages and disadvantages?

Answer 14

cross-sectional study, longitudinal study, cross-sequential design

Question 15

cross-sectional study:

Answer 15

in developmental research, a study that tests different age groups at the same time

Question 16

longitudinal study:

Answer 16

in developmental research, a study that tests individuals in a single cohort over the course of time

• The practical problem is that the researcher has to wait years to complete the study as the cohort ages.
• theoretical problem with a longitudinal study is that it con- founds age with time of testing

Question 17

secular trend:

Answer 17

a change that is taking place in the general population over time (the term has nothing to do with religion): general changes that take place in a society that may influence the results of your study

Question 18

cross-sequential design:

Answer 18

design used to help separate developmental, cohort, and secular effects

• This design tests individuals from two or more cohorts at two or more times. Suppose we take four groups of people, born in 1990, 1980, 1970, and 1960, and see what percentage of each group can program a DVR. Suppose also that we test them in the years 2000, 2010, and 2020.

Question 19

time-lag effect:

Answer 19

in a cross-sequential design, the effect resulting from comparing subjects of the same age at different times

Question 20

program evaluation:

Answer 20

a set of techniques for determining the effectiveness of a social service program

• Quasi-experimental designs are often used in program evaluations, because clients of the program are more likely to be assigned, rather than to be randomly allocated, to groups for comparison
• Can test against people who have not been assigned the intervention