Non-response bias... Is primarily a threat to internal validity Is primarily a threat to external validity...

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Non-response bias... Is primarily a threat to internal validity Is primarily a threat to external validity Occurs when true random sampling has been used Occurs when people drop out of a study over time Non-response bias... Is primarily a threat to internal validity Is primarily a threat to external validity Occurs when true random sampling has been used Occurs when people drop out of a study over time