When reviewing experimentation results, it is crucial to understand the significance of pre-experiment data. This data serves to highlight any potential pre-existing differences between the groups involved in the experiment. Such differences, if not accounted for, could lead to skewed results by attributing these inherent discrepancies to the experimental intervention.
To mitigate this issue, a technique known as CUPED (Controlled-Experiment Using Pre Experiment Data) is employed.
CUPED is instrumental in reducing variance and pre-exposure bias, thereby enhancing the accuracy of the experiment results. It is important to recognize, however, that CUPED has its limitations and cannot completely eliminate bias. Certain metrics, particularly those like retention, do not lend themselves well to CUPED adjustments.
In instances where bias is detected, users are promptly notified, and a warning is issued on the relevant Pulse results. The use of pre-experiment data is thus integral to the process of identifying and adjusting for pre-existing group differences, ensuring the integrity of the experimental outcomes.