14 Sample may not be representative of the group you are trying to generalize to, so external validity can be diminished. 15 Marker tests are clean measures of a trait or domain. The correlations among dis-similar traiits are low. As the reliability of either measure decreases, the ceiling for the validity coefficient is lowered. Two variables cannot be perfectly correlated when there exists some measurement error.
Stability examines reliability over time.
Internal consistency examines reliability at a specific time. 3 Expected validity when no measurement error present. There is reason to go back and examine data collection procedures. 8 Examine data collection procedures in search of opportunities to minimize measurement error, re-collect data and estimate reliability for new measures. In this case, the error present that was not attributable to variabiity across factors.