Probability and significance

• Before analysing data, a clear hypothesis must be outlined, which can be either directional or non-directional
• A directional hypothesis states the expected direction of the findings based on previous research in the field of psychology
• A non-directional hypothesis is selected when there is little or conflicting evidence in the field of psychology
• Use of Statistical Tables and Critical Values:

  • After conducting a statistical test, the calculated value is compared with the critical value in the statistical tables
  • The critical value varies with the statistical test used
  • Factors to consider when determining the critical value:
  • One-tailed (directional hypothesis) or two-tailed (non-directional hypothesis) test
  • Number of participants in the sample
  • Level of significance or p-value (typically 0.05 in psychology)
• Type I and Type II Errors:

  • Type I error: Null hypothesis is rejected when it is true (false positive)
  • Type II error: Null hypothesis is accepted when it is false (false negative)
  • Likelihood of errors is influenced by the level of significance chosen (p-value)
  • A p-value of 0.05 is commonly used in psychology to balance the risk of type I and type II errors