Analyzes observed differences in sample units that are subjected to two different inputs. To use the paired t-test, you must subject the exact same sample units to both levels of the input variable to remove potential effects due to differences in the sample units themselves, which might mask the effect due to the change in the input. For example, you want to test whether two types of tires result in differences in gas mileage. The variation in gas mileage due to different cars in the sample would be much greater than variation due to different tires. The paired t-test accounts for the differences in cars.
|When to Use||Purpose|
|Mid-project||Fixing an input at two different settings (levels) helps to determine which inputs have significant influence on mean of the output.|
|Mid-project||Verify changes to inputs result in significant differences from the pre-project mean, provided you can test on the same units as those in the pre-project sample.|
Continuous Y (output), one X (input) at two levels.