A fitness instructor investigated the effects of a new virtual reality (VR) visualization technique using two separate groups of club runners:

• Group X: one group of runners completed a 10-minute VR visualization session before a 5km time trial.
• Group Y: a different group of runners rested quietly for 10 minutes before the same 5km time trial.

Afterwards, the instructor calculated the average completion time (in minutes) for each group, as shown in Table 1.

Table 1: Average 5km completion times (minutes) for Group X and Group Y

The instructor concluded that the VR visualization session may not have been the only factor that caused the difference in average completion times between Group X and Group Y. The instructor was concerned because the runners in each group had different baseline running abilities.