"Tara would like to measure how social college students are with friends at lunch compared to at dinner. She times how long students make eye contact in the dining hall with one another as a measure of their sociability. Tara finds that students at dinner are significantly more sociable based on this measure. What type of validity may be insufficient in this study?"

Construct validity refers to how accurate a study can measure / provide data about the things it claim in the initial description. From the case above, Tara's study claim that it measure 'how social college students are with friends at lunch compared to at dinner' .

In order to measure this, Tara only use 'duration of eye contact' as an indicator of measure it.

The thing is, Social interaction is done with many type of actions, including spoken communication, skin contact, laughter, opened body language ,etc. Only using eye contact will cut off the people who rely their socialization process on these other actions. Because of this, we can say that this study is lacking in validity.