Probability and Statistics

• Define probability

  A measure of the likelihood that a particular event will occur where 0 indicates statistical impossibility and 1 statistical certainty
• Why do we use statistical testing in psychological research?


  To determine whether to accept the alternative or null hypothesis and determine if results are statistically significant.
• What is the usual level of significance for psychological statistics?


  0.05 / 5%
• Statistical Errors: What is a Type I error?

  Null hypothesis incorrectly rejected, alternative incorrectly accepted - false positive
• Statistical Errors: What is a Type II error?


  null hypothesis incorrectly accepted when it should’ve been rejected - false negative
• When is it more likely for a Type I error to occur?


  When significance levels are too high, e.g. 0.10 instead of 0.05 or 0.01
• When is a Type II error more likely to occur?

  When significance levels are too low - potentially significant values may be missed
• Define what is meant by critical value in statistical testing


  the critical value is the NUMERICAL BOUNDARY between accepting or rejecting the null hypothesis, based on the level of significance.
• What is another term for one-tailed hypotheses?


  Directional
• When would you use a one-tailed hypothesis?


  When there is a specific significant difference, e.g. increase or decrease. Also if there’s been previous research on the topic
• What 3 pieces of information do you need to use for statistical tables?

  One-tailed or two-tailed hypothesis, number of participants and level of significance (p value) - assume 0.05 unless stated otherwise
• Define significance


  A statistical term that tells us how sure are that a difference or correlation exists. A ‘significant’ result means the researcher can reject the null hypothesis