Statistical testing and the sign test

• Why do we use statistical testing?

  Provides a way of determining whether differences between variables are statistically significant or occurred by chance
• What is the difference between a one-tailed and two-tailed test?

  1. One-tailed test = directional hypothesis

  2. Two-tailed test = non-directional hypothesis
• What is the sign test?

  A statistical test used to analyse the difference in scores between related items.
• What are 3 conditions for using a sign test?

  1. Need to be looking for a difference rather than an association

  2. Use a repeated measures design

  3. Nominal data
• What is probability?

  The likelihood that certain events will occur
• What is the accepted level of probability in Psychology?

  0.05
• What does the calculated value have to be significant to?

  It has to be equal or lower than the critical value
• What does it mean if the researcher accepts the hypothesis?

  There is less than 5% probability that the results occurred by chance
• Why might a researcher adopt a significance level of 0.01?

  When researchers need to be more confident that results were not due to chance - e.g. when research may involve human cost (new drugs being trialled)
• Which 3 pieces of information do you need to locate the critical value?

  1. The significance level desired

  2. The number of participants in the investigation (the N value)

  3. Whether the hypothesis is directional (one-tailed) or non-directional (two-tailed)
• What does the calculated value have to be to be significant?

  It has to be equal to or lower than the critical value (calculate value = S value)
• EXAMPLE - I have an S value of 5 and the critical value 3

  The results are not significant. I will accept the null hypothesis because the S value of 5 is greater than the critical value 3.