I’m trying to find out whether the percentage of students who are satisfied with a service (statistically) significantly changes year-to-year.

This would be easy enough to do with interval data with a t-test (scale of 1-4, looking at the mean), but I would like to know how to compare binary variables (interval data binned into 2 categories: Satisfied vs. Dissatisfied).

**Data**

Samples are drawn randomly, sizes are approximately 900 cases for each year. Population size is approximately 17,000.

Interval satisfaction data (scale of 1-4) is collapsed into dichotomous satisfaction data (1,2=Satisfied / 3,4=Dissatisfied). Percent Satisfied is reported, based on the dichotomous data.

**What I want to find out**

Are there significant differences between the reported Percent Satisfied between 2 given years?

Any advice you could provide would be much appreciated.