UCSB COMM 88 EXAMINATION SCRIPT
2026 COMPLETE QUESTIONS WITH FULL
SOLUTIONS
◉ What is a time-series experiment design?
Answer: Track many observations over time, before and after
manipulation
Single-group interrupted time series design: looks for an
interruption in graph where intervention was introduced
Multiple time series design: series of periodic measurements taken
from two groups (experimental & control)
◉ What are the pros of a single-group interrupted time series
design?
Answer: Improves upon the "one group pretest-posttest"
Good for comparing before and after some IV manipulation
Y1 Y2 Y3 Y4 X1 Y5 Y6 Y7 Y8 (group 1)
◉ What are the pros of a multiple time series design?
Answer: Good for comparing before and after some IV manipulation
and comparing 2 or more groups with each other
Y1 Y2 Y3 Y4 X1 Y5 Y6 Y7 Y8 (group 1)
, Y1 Y2 Y3 Y4 X2 Y5 Y6 Y7 Y8 (group 2)
◉ To ensure high internal validity...
Answer: have a truly random way of splitting up your groups and
minimize/eliminate the "3rd variable" problem
◉ To ensure high external validity...
Answer: Carry out experiment in the field
Have other researchers replicate your work
Make your subjects more representative
Use different research strategies to test the same hypotheses
◉ What 7 things can affect internal validity?
Answer: 1. Selection bias
2. History effect
3. Maturation
4. Statistical regression toward the mean
5. Mortality
6. Testing
7. Reactivity effects, including placebos
◉ When does selection bias happen?
2026 COMPLETE QUESTIONS WITH FULL
SOLUTIONS
◉ What is a time-series experiment design?
Answer: Track many observations over time, before and after
manipulation
Single-group interrupted time series design: looks for an
interruption in graph where intervention was introduced
Multiple time series design: series of periodic measurements taken
from two groups (experimental & control)
◉ What are the pros of a single-group interrupted time series
design?
Answer: Improves upon the "one group pretest-posttest"
Good for comparing before and after some IV manipulation
Y1 Y2 Y3 Y4 X1 Y5 Y6 Y7 Y8 (group 1)
◉ What are the pros of a multiple time series design?
Answer: Good for comparing before and after some IV manipulation
and comparing 2 or more groups with each other
Y1 Y2 Y3 Y4 X1 Y5 Y6 Y7 Y8 (group 1)
, Y1 Y2 Y3 Y4 X2 Y5 Y6 Y7 Y8 (group 2)
◉ To ensure high internal validity...
Answer: have a truly random way of splitting up your groups and
minimize/eliminate the "3rd variable" problem
◉ To ensure high external validity...
Answer: Carry out experiment in the field
Have other researchers replicate your work
Make your subjects more representative
Use different research strategies to test the same hypotheses
◉ What 7 things can affect internal validity?
Answer: 1. Selection bias
2. History effect
3. Maturation
4. Statistical regression toward the mean
5. Mortality
6. Testing
7. Reactivity effects, including placebos
◉ When does selection bias happen?
