A researcher wants to conduct a correlational study on the effect of alcohol on mood. Specifically, the researcher believes the more beers a person drinks', the happier and more outgoing a person becomes. The proposed experimental protocol will require participants to consume 16 beers over a period of four hours and during each hour mood and outgoingness will be measured. Ethical issues aside, what is a potential problem of interpreting this data with a correlation coefficient (Pearson's r)