Statistical test for frequency data changes over time with one group of subjects?

Question

I have collected data over 8 years for 44 students on the number of episodes of physical aggression that have occurred with each student for each of the 8 years. I have calculated the percentage change from the first year to the last year for each of the 44 students. 38 of these 44 students showed a decrease in frequency of these events over the course of the 8 years and the average decrease was 79% from baseline. Is there a statistical test I should be conducting to analyze these results or do they just stand as descriptive stats? There is no control group.

Answer 1

Trying to perform a standard z or t test with just the data from start to finish is not appropriate since you have no control group to compare to.  Right now, it is mainly a descriptive stat.

 

However, since you have data from each of the 8 years, you could perform time-series analysis to see if there is truly a trend, and it may allow you to to build a predictive model for how student aggression episodes decrease over time.  It depends on what the goal is that you are trying to accomplish.