Should Megan Use Matching Methods With Her Survey?

Megan the exercise freak and health coach believes that eating out at restaurants can be good for people because it motivates them to exercise more the following day. She creates an online survey for whether they ate out at a restaurant the previous Saturday, and whether they spent any time exercising the following Sunday. After several thousand responses, she finds a positive correlation between eating at a restaurant and exercising the following day. Why might why might she want to use matching methods to assess whether there is a causal effect?

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She needs to match people to run a regression
She doesn't: if there is a correlation between the two variables, then she has found her effect
She needs to create treatment and control groups to find a causal effect.
Because people who eat out might have a higher propensity to exercise as well.

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Should Megan Use Matching Methods With Her Survey?

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