Fellows!

I'm sorry for what is a probably basic question but I'm really needing help.

I'm currently doing my Bachelors thesis and I'm taking a diff-in-diff approach, It's all adding up, but i need to asses the Common Trends Assumption in a way other than graphically.

My data is structured by county, quantity of congregations (which is what i need to prove are parallel in time), population and then dummies for treatment areas and treatment moment. I have data for 1952, 1971, 1980, 1990, 2000 and 2010, treatment occurs between 2000 and 2010.

When I graph the avg quantity of congregations between the treated and control it's clear that they're parallel, but I need to be able to confirm otherwise.

Any help?

Thanks in advance!!