Type II Error
A Type II error occurs when you fail to reject H₀ even though H₀ is false. The probability of a Type II error is denoted β. The power of a test is 1 - β, the probability of correctly rejecting a false H₀. Type II errors represent false negatives or missed detection of a true effect.
Real World
A clinical trial for a new antibiotic failed to reject the null hypothesis of 'no difference', but the drug later proved effective in larger studies — the original small trial had committed a Type II error.
Exam Focus
State Type II error as 'fail to reject H₀ when H₀ is false'; explicitly link it to insufficient sample size if asked.
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