Probability and significance

• What is a null hypothesis?

  Predicts there will be no effect between variables
• What is the alternative hypothesis?

  Predicts an effect between variables - either directional or non-directional
• What is significance?

  The researcher can state that the relationship between variables is due to more than just chance - they can accept the alternative hypothesis and reject the null hypothesis
• What are inferential statistics?

  A way of determining whether differences or relationships between variables are statistically significant or have occurred by chance
• What is probability in the context of statistical testing?

  The likelihood that the data obtained is due to chance - rather than manipulation of the IV
• What is the usual level of significance used in psychology?

  p ≤ 0.05 (or 5%)
• When might psychologists adopt a more stringent significant level of 0.01?

  - When there is a human cost, e.g. considering the effects of a new drug

  - When the results are theoretically important
• What is a type I error?

  Rejection of the null hypothesis when it should have been accepted (also known as a 'false positive' - finding it significant when it wasn't)
• What is a type II error?

  Wrongly accepting the null hypothesis (known as a 'false negative' - finding it not significant when it was)
• When are researchers more likely to make a type I error?

  When the significance level is too lenient (0.1 or 10%)
• When are researchers more likely to make a type II error?

  When the significance level is too strict (0.01 or 1%)