The threat to validity that is likely to occur in the scenario above is Selection Bias.
<h3>What is Selection Bias?</h3>
This occurs when a researcher has control and intentionally chooses those who are going to be researched, observed, or studied. To eliminate this bias, the scientist must ensure that the sample population is selected very randomly.
Other threats to validity are:
History
Maturation
Attrition
Social Interaction
Instrumentation
Testing
Regression to the mean, etc.
Please see the link below for more about Threat to Validity:
