A2 Psychology Unit 4 Research Methods

   1. In the exam you could be asked to choose a statistical test or to justify why...
a. significance level (this will usually be stated as O.O5)
            b. one-tailed or two tailed test
                 ...
A2 Psychology Unit 4 Research Methods

   6. In the exam you could be asked to choose a statistical test or to justify why...
a. significance level (this will usually be stated as O.O5)
            b. one-tailed or two tailed test
                 ...
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  1. 1. A2 Psychology Unit 4 Research Methods 1. In the exam you could be asked to choose a statistical test or to justify why a particular test was chosen. There are 3 things you need to consider. Complete the flow chart below to show which statistical test should be chosen in a study Is the… yes n o Is the .. yes n o Is the .. yes n o 2. Each statistical test involves doing a calculation which results in a test statistic. In the exam you could be given an observed value and asked about which test statistic it is. Show the test statistics for each of the three tests listed below The Mann-Whitney test statistic is The Spearman’s correlation test statistic is The Chi-square test statistic is The Wilcoxon test statistic is 3. The observed value is so called because it is the value calculated from the observed results in a study. You will not be asked to calculate an observed value in the exam. However you could be asked to decide if an observed value is significant by comparing it to a critical value in a table. (which will be provided) What is meant by the term critical value? 4. Things that are needed to find the critical value are
  2. 2. a. significance level (this will usually be stated as O.O5) b. one-tailed or two tailed test i. What does this depend on) c. degrees of freedom (df) i. For each test find out how this is decided. This may be how df is calculated or what else (e.g. N ) is needed instead For the Mann-Whitney test For Spearman’s correlation For Chi-square test df = For Wilcoxon test 5. Having found the critical value in a table you need to compare it to the observed value calculated from the results. This will decide whether the pattern in the results (difference or correlation) is significant. Whether the observed value needs to be greater or smaller than the critical value varies between tests (it needs to be greater for chi-squared and Spearman’s and smaller in Mann-Whitney and Wilcoxon) but this will be stated for you in the exam. Using the critical value tables in your text books, decide whether the following observed values are significant at p=0.05 • Rho = 0.410 for a one tailed test where N =20 • Rho = 0.5 for a two tailed test where N = 10 • Х2 = 3.24 for a two tailed test with a 2x2 contingency table • Х2 =5.00 for a one tailed test with a 3x2 contingency table • U = 16 for a one-tailed test with 9 PPs in one group and 8 in the other group. • U= 76 for a two tailed test with 30 PPs split equally between the 2 conditions • T= 54 for a one tailed test with 25 PPs • T= 105 for a two tailed test with 20PPs 6 Look at question 5 (e) on page 297 of your book. How confident would you now feel about attempting this?
  3. 3. A2 Psychology Unit 4 Research Methods 6. In the exam you could be asked to choose a statistical test or to justify why a particular test was chosen. There are 3 things you need to consider. Complete the flow chart below to show which statistical test should be chosen in a study Is the…data nominal yes Chi-square n o Is the ..test for a correlation Spearman’s rho yes n o Is the ..design independent groups yes Mann-Whitney U n o Wilcoxon T 7. Each statistical test involves doing a calculation which results in a test statistic. In the exam you could be given an observed value and asked about which test statistic it is. Show the test statistics for each of the three tests listed below The Mann-Whitney test statistic is U rho The Spearman’s correlation test statistic is The Chi-square test statistic is ‫2ﭏ‬ The Wilcoxon test statistic is T 8. The observed value is so called because it is the value calculated from the observed results in a study. You will not be asked to calculate an observed value in the exam. However you could be asked to decide if an observed value is significant by comparing it to a critical value in a table. (which will be provided) What is meant by the term critical value? The cut-off value for the observed value if the null hypothesis is to be rejected 9. Things that are needed to find the critical value are
  4. 4. a. significance level (this will usually be stated as O.O5) b. one-tailed or two tailed test i. What does this depend on) Directional or non-directional hypothesis c. degrees of freedom (df) i. For each test find out how this is decided. This may be how df is calculated or what else (e.g. N ) is needed instead For the Mann-Whitney test N1 and N2 For Spearman’s correlation N For Chi-square test df = (Rows – 1) x (columns – 1) For Wilcoxon test N 10. Having found the critical value in a table you need to compare it to the observed value calculated from the results. This will decide whether the pattern in the results (difference or correlation) is significant. Whether the observed value needs to be greater or smaller than the critical value varies between tests (it needs to be greater for chi-squared and Spearman’s and smaller in Mann-Whitney and Wilcoxon) but this will be stated for you in the exam. Using the critical value tables in your text books, decide whether the following observed values are significant at p=0.05 • Rho = 0.410 for a one tailed test where N =20 sig • Rho = 0.5 for a two tailed test where N = 10 not sig • Х2 = 3.24 for a two tailed test with a 2x2 contingency table not sig • Х2 =5.00 for a one tailed test with a 3x2 contingency table sig • U = 16 for a one-tailed test with 9 PPs in one group and 8 in the other group.sig • U= 76 for a two tailed test with 30 PPs split equally between the 2 conditions sig • T= 54 for a one tailed test with 25 PPs sig • T= 105 for a two tailed test with 20PPs not sig 6 Look at question 5 (e) on page 297 of your book. How confident would you now feel about attempting this?

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