Inferential testing

• The alternate hypothesis: H1


  There will be an affect
• The null hypothesis: H0


  There will be no effect
• Statistical Test


  Allows us to decide which hypothesis is true and whether we accept or reject H0
• What is the accepted probability where the null hypothesis is rejected?

  5%
• Type I error


  Significance is too lenient (10%) and you reject null hypothesis when you should have accepted it
• Type II error


  Significance is too stringent (1%) and you accept null hypothesis when you should have rejected it
• Establishing Significance

  1. N value is the n.o of PPs
  2. Calculated value depends on the test you do
  3. Significance level (0.05 unless told otherwise)
  4. Is it one tailed or two tailed
  5. Critical value found using table given
• Explain why statistical tests are used in psychological research


  Used to establish whether we should accept or reject the null hypothesis and whether the results are significant
• What are the 3 main things to consider when choosing a statistical test?

  1. Test of difference or correlation
  2. Independent, Repeated Measures or Matched Pairs design
  3. Levels of Measurement
• Sign Test steps

  1. Find difference between 2 sets of data but you only need the + and - signs
  2. Add the + and - signs and ignore the 0 values
  3. The least frequent sign is your S value also known as calculated value
  4. Your N value is the number of PPs you have once you get rid of the 0 value PPs
  5. Find critical value with the table given and compare with your S value
• What is meant by a Type II error? Explain why psychologists normally use the 5% level of significance in their research

  A Type II error happens when you accept the null hypothesis when it should have been rejected (false negative). Using 5% is a balance between the two errors which prevents making the two types of errors