Question

A recent study suggests that acetaminophen can decrease people psychological pain (DeWallet al, 2010). Researchers decides to see if this claim is true or not. Researchershad randomly sampled 62 volunteers and split them into an experimental group (that received acetaminophen) and a control groups (that received a placebo). Both groups read socially painful stories and rated how painful the experience would be for them.

For this question, its one-tail test but why it's one-tail not two-tail.

Answer 1