DESIGN

STRENGTHS

WEAKNESSES

STATIC COMPARISON

• Better than nothing
• Can be useful for preliminary examination

• Pre-existing differences between groups are likely to be the cause of the different levels of the problem
• Cannot determine if the response came before or after the pre-existing differences
• Cannot eliminate the possibility that pre-existing trends created the results

PRE-POST

• Simple and quick to implement
• Can easily be used with surveys
• Can provide a reasonable estimate of the change in a problem following a response

• Can only show short-term changes in problems
• Cannot account for pre-existing trends
• Very weak at eliminating alternative explanations for the change in the problem
• Cannot account for the possibility that some other factor occurred at the same time as the response, and caused the problem to change

INTERRUPTED TIME SERIES

• Very easy to use with data routinely collected over many time periods
• Can eliminate pre-existing trends and many other alternative explanations

• Very hard to use if special data-collection efforts, such as surveys, are used to measure the problem
• Cannot account for the possibility that some other factor occurred at the same time as the response, and caused the problem to change
• Results take a long time to be established
• Difficult to interpret when there are few problem events per time period before the response

PRE-POST WITH CONTROL

• Can easily be used with surveys
• Can account for the possibility that some other factor occurred at the same time as the response, and caused the problem to change

• Can only show short-term changes in problems
• Requires a problem-troubled control group that will not get the response and is similar to the response group

MULTIPLE TIME SERIES

• Easy to use with data routinely collected over many time periods
• Can eliminate pre-existing trends and many other alternative explanations
• Can account for the possibility that some other factor occurred at the same time as the response, and caused the problem to change

• Very hard to use if special data-collection efforts, such as surveys, are used to measure the problem
• Requires a problem-troubled control group that will not get the response and is similar to the response group
• Results take a long time to be established
• Difficult to interpret when there are few problem events per time period before the response