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advanced applied science: GCE A2 UNITS © The Nuffield Foundation 2008 ACTIVITY BRIEF Wisconsin card sorting test correlational studies The science at work Correlational studies are investigations in which scientists attempt to establish associations. Psychologists and other research scientists frequently wish to test the extent to which one factor is associated with another. There may be a positive association, where measurements or scores for one factor increase in line with the values obtained for another factor. Or there may be a negative association where one increases as the other decreases. Or there may be only a very weak association or no association at all. For example, is there an association between how hard you work and the grade that you obtain for Applied Science? Is this a strong or weak association and is it positive or negative? By designing their investigations to collect the correct kind of data, it is possible for scientists to use a statistical test called a correlation coefficient to test the strength of an association. Scores can lie anywhere between +1 for a perfect positive association, through 0 for no association at all, to -1 for perfect negative association. A note of caution: correlation does not prove causality; it only shows the nature of the association between two variables. If a change in one variable is causing the change in another, this has to be established by further investigation, or by reference to theory and evidence from elsewhere. Hard work does not make a good grade certain, as there are other factors at work. But it does make it more likely! Your brief You will be given a problem to investigate using a correlational study, with the use of a statistical test to analyse the data. You will need to calculate correlation coefficients for paired data to assess the extent to which they show a linear (straight line) relationship. This association may be positive, if both sets of scores go up at the same rate together, or negative if one goes up as the other goes down. You can do an ‘eyeball’ test first, by plotting scatter graphs of one variable against another. But how do you decide when a set of plots is close enough to a straight line to be confident that you have shown a linear relationship? The statistical testing will give you a probability value to measure how confident you can be in deciding whether there is a significant degree of correlation or not. You can form conclusions based on this and be reasonably sure that you are correct. Use Practical sheet: Conducting a correlational study using the WCST You may find these fact sheets helpful: Fact sheet: Background to statistics; Fact sheet: Using Excel for descriptive statistics; Fact sheet: Using Excel for inferential statistics. Ask your teacher if you would like copies. Wisconsin card sorting test correlational studies: page 1 of 6 advanced applied science: GCE A2 UNITS © The Nuffield Foundation 2008 PRACTICAL SHEET Conducting a correlational study using the WCST Using correlation coefficients Your teacher will give guidance on choosing an investigation to meet the unit requirements. You will: obtain two sets of paired data, i.e. each value in one set will be paired with a definite value in the other set analyse these data by using a correlation coefficient. Make sure that you are clear about the investigation you are going to carry out, so that you know which scores to use in your analysis. Meeting requirements for the unit Your teacher may wish you to carry out and report your work in a particular way to meet the requirements of this unit. For example, the use of Excel makes calculations simpler and more likely to be error free, but your specification may require you to carry out your first calculations and record them by hand. Check what you need to do with your teacher. Requirements You will need: test materials for the version of the WCST that you trialled. Either 64 item card set, four stimulus cards and a Results sheet for each test with scoring instructions or a computer with a programme for presenting the test and recording the results. a quiet area where the participants will not be distracted you will need a minimum of 5 participants, but more would be better Note that the larger your sample, the less likely it is that results will be markedly affected by chance. A small sample may not demonstrate an effect shown by a larger sample. Health and safety You should always carry out a risk assessment before you start any practical work. When using human participants, you should take into account any ethical considerations. In this case, you should fully advise any participant of what you expect them to do and the purpose of your investigation. Procedure Follow the instructions given to you by your teacher. Use one of the following: Correlational study 1: Testing for redundancy in the WCST Correlational study 2: Testing the reliability of the WCST Correlational study 3: Finger length and the WCST Wisconsin card sorting test correlational studies: page 2 of 6 advanced applied science: GCE A2 UNITS © The Nuffield Foundation 2008 Correlational study 1: Testing for redundancy in the WCST Background Some psychologists believe that there are some redundancies in the scoring of the WCST. That is, some scores show a strong correlation and are therefore likely to be measures of the same effect. When two scores fail to show a correlation, this is useful to clinicians and researchers because it is evidence that they are measuring the effect of different brain mechanisms. You can test this for yourself. Your task Your task is to review the scoring system for the WCST (or your own version) and predict which scores show significant correlation (i.e. show redundancy) and which scores are independent measures of aspects of executive control. Procedure 1 Decide which scores you will use. Make at least one prediction of a correlation and one prediction of no correlation. 2 Write suitable hypotheses for testing using a coefficient of correlation. 3 Obtain WCST (or equivalent) scores for at least five participants. 4 Plot scatter graphs. 5 Apply an appropriate statistical test to your results. 6 State your conclusions and evaluate your investigation. Wisconsin card sorting test correlational studies: page 3 of 6 advanced applied science: GCE A2 UNITS © The Nuffield Foundation 2008 Correlational study 2: Testing the reliability of the WCST Background Does the WCST or your version give consistent results? If a test shows low reliability, predictions based on the data will not be valid. Clinicians and researchers need to be able to rely on the tests that they use. Your task is to conduct a test and retest for each individual and see if the scores show good correlation. You will need to decide how long to leave between the tests, bearing in mind that boredom or practice effects may affect the scores if tests are run immediately one after the other. Procedure 1 Decide which scores you will use. 2 Write suitable hypotheses for testing using a coefficient of correlation. 3 Obtain at least two sets of WCST scores (or equivalent) for at least five participants. 4 Design your investigation to take into account factors other than test reliability which may affect your results. You may wish to test for factors affecting scores when two tests are run back to back. 5 Plot scatter graphs. 6 Apply an appropriate statistical test to your results. 7 State your conclusions and evaluate your investigation. (Remember that unreliable results may not be due to the test itself.) Wisconsin card sorting test correlational studies: page 4 of 6 advanced applied science: GCE A2 UNITS © The Nuffield Foundation 2008 Correlational study 3: Finger length and the WCST Background Development of certain brain areas associated with spatial and mathematical skills is believed to be linked to exposure to testosterone in the womb. Do any of these areas have a role to play in performance of the WCST? Testosterone is also thought to affect the relative lengths of the first (index) finger and third (ring) finger. Ratios of the measurements of these fingers can be used to estimate the exposure to the hormone in the womb. Length of first finger is divided by length of third finger for both hands and an average is obtained. A smaller ratio (longer third finger) indicates greater prenatal exposure to testosterone and increased ability in spatial and mathematical tests. For example, the higher numeracy SAT scores shown by boys have been linked to smaller digit ratios. Similar higher literacy SAT scores shown by girls have been linked to higher digit ratios. These are thought to be due to the relatively higher exposures to oestrogen. Your brief Your task is to measure finger lengths of participants who have completed the WCST and test for correlation of test scores with their first and third finger ratios. Additional requirements You will need a ruler with mm divisions, or better, callipers for measuring finger lengths. Procedure 1 You will use the scores for categories completed and perseverance errors as measurements of executive control. Decide if there are any other scores that you would like to test for correlation with finger ratios. 2 Write suitable hypotheses for testing using a coefficient of correlation. 3 Obtain the chosen WCST scores (or equivalent) for at least five participants. 4 Measure first and third finger lengths to the nearest mm (or if possible, nearest 0.1 mm), making sure the results are paired with the WCST scores. 5 Calculate the mean of the digit ratio for both hands: length of first finger/length of third finger. 6 Plot scatter graphs of WCST scores against mean digit ratios. 7 Apply an appropriate statistical test to your results. 8 State your conclusions and evaluate your investigation. Wisconsin card sorting test correlational studies: page 5 of 6 advanced applied science: GCE A2 UNITS © The Nuffield Foundation 2008 Teacher notes This activity links to OCR A2 Unit 13 The mind and the brain. The activity follows on from the work associated with Activity brief: Investigating the Wisconsin card sorting test. Further guidance may be found in the Teacher notes there. Wisconsin card sorting test correlational studies: page 6 of 6