We are looking at 60 days of a product sales data from a single store, 30 days before and 30 days after the intervention (second display).
We need to evaluate if introduction of second display increased sales.
Is paired sample t-test valid test for this situation?
Data is continuous, there are no outliers in the before / after groups, difference (fist/second/third....etc. day of control period minus fist/second/third....etc. day after intervention) is normally distributed.
Something tells me that paired sample might not be the "correct" test, but a friend from Quality Control tells me that they constantly use paired-samples t-test with the exact same type of data (multiple data points before and after the intervention from same subject)