Statistical Testing

• why do we use statistical testing

  to check results are significiant and not due to chance - the difference in the DV is truly due to manipulation of the IV
• whats the accepted probability in psychology

  0.05 or 5%
• what does 5% probability mean

  theres a less than 5% chance the results occurred by chance/less than 5% chance the difference in the DV was due to something other than the manipulation of IV
• under what circumstances will the probability be 0.01 or 1%


  if the research involves human cost or one-off investigation where theres a higher level of significance
• when do you use a sign test (3 points)

  - looking for a difference not association (experiment not correlation)

  - used repeated measures

  - when data is nominal (categorical)
• what is a calculated value


  the result of the statistical test (the less frequent sign +/-)
• what is a critical value


  the value given in the table of critical values
• what do you do with the calculated & critical values

  compare them to see if result is significant
• when do you use a two-tailed experiment

  with a non-directional hypothesis
• when do you use a one-tailed experiment


  with a directional hypothesis
• what must the calculated value be

  equal or lower than the critical value to be significant
• what are the 6 steps of a sign test

  1. subtract scores of one condition from the other condition

  2. if any Ps perform the same in both (0) ignore them, adjust N value

  3. write either + or - next to each

  4. add up number of + and -

  5. add up amount of less frequent sign = calculated value

  6. compare calculated & critical values (if calculated is less than or equal to critical values = significant)