A study was conducted to assess whether 5 weeks of training with virtual reality (VR) can reduce the risk of falls in adults. Thirty-four older adults underwent 15 VR training sessions consisting of walking on a treadmill with a VR simulation. At the end of the VR training program, participants showed improved mobility and gait speed. In the abstract the authors conclude that “[t]readmill training with VR appears to be an effective and practical clinical tool to improve mobility and reduce falls in older adults.” Do these results indicate that VR training can cause improvement in mobility and gait speed among older adults? What essential component of both controlled experiments and observational studies is missing from this study? (Source: Shema et al., “Improved mobility and reduced fall risk in older adults after five weeks of virtual reality training,” Journal of Alternative Medical Research, 9(2), 171–175.)