Let's run through a few questions relating to decisions about the sample in a study using the following example.

I want to determine if there is a link between the amount of screen time college students are exposed to each week and self-reported ratings of quality of sleep. To determine if there is a link, I formulate the following research question and hypotheses. Help me make decisions about sampling.

RQ: Is there a link between the amount of screen time college students are exposed to each week and self-reported ratings of quality of sleep?

Null hypothesis: There is not a link between the amount of screen time college students are exposed to each week and self-reported ratings of quality of sleep.

Alternative hypothesis: There is a (statistically significant) link between the amount of screen time college students are exposed to each week and self-reported ratings of quality of sleep. Have I made any predictions about directionality? How do you know?