Advanced Quantitative Methods, statistic
Advanced Quantitative Methods Assessed Coursework: Worksheet 3 Answer all sections. Section A (50 marks) Mindfulness is a meditation-like practice that encourages attentional focus and reduces mindwandering (Williams, 2014). While there is evidence to support the efficacy of mindfulness techniques, the underlying cognitive and neural mechanisms by which mindfulness affects behavioural outcomes are unclear. Recently, mindfulness was tested in vulnerable populations suffering from trait vulnerability to anxiety and depression with the aim to enhance attentional control and reduce anxiety and depressive-linked attentional biases for threatening material. A major characteristic of anxious and depressed individuals is an impaired ability to disengage from the processing of threatening material and ruminative thoughts due to impairments in attentional control (see Berggren & Derakshan, 2013, for a review). The study wanted to see if mindfulness will result in a reduction in attentional biases for threat in anxious and depressed samples. There were two groups of Anxious (not depressed) and Depressed (not anxious) participants: Half of whom underwent a 20 minute single session mindfulness training, with the other half a control training that involved reading a passage from a book. Assessment of attentional biases for threat was made using a visual search task where participants searched for a ‘neutral’ target face amongst a crowd of angry faces, and attentional dwell time (in ms) on each crowd face, prior to target face was recorded using eye-movements (participants completed other conditions but for the purpose of the analysis here only this condition will be discussed). Thus, longer dwell times indicate an impaired ability to disengage from the processing of the face. Participants completed a version of this task before training, a similar version immediately after training, and a week after training to see if any change in attentional bias as a result of training was sustained. The data is in the file: Mindfulness.sav. Now attempt the following: 1. Sketch and describe the design of this experiment; identify the factors and their corresponding levels. Formulate two hypotheses for your experimental manipulations of interest. [6 marks] Conduct an appropriate ANOVA to test for the main effects and interaction effects of interest. Address the following questions. 2. Produce two graphs that show the effects of mindfulness vs control training across time for each of the anxious and depressed groups separately. Comment on the pattern you see. [12 marks] 3. Report and comment on the respective three-way interaction effect that would corroborate your observation in Q2 above. What would you conclude from this interaction? Using linear and quadratic contrasts elaborate on the effects of training over time for your groups. [12 marks] 4. Perform simple effects analyses to follow-up on the interaction effect discussed in Q3, as you see fit. What do you need to control for with multiple contrasts? [10 marks] 5. Comment on the main effect of Group and the possible interaction between Group X Training. How can these effects bias the influence of time on training? [10 marks] Section B (24 marks) It has been argued that worrying can adversely affect one’s performance levels by reducing attentional focus and increasing distractibility. According to Attentional Control Theory (Eysenck, Derakshan et al., 2007; Derakshan et al., 2009) worrying interferes with processing efficiency on tasks by using up limited capacity resources of the working memory system, leaving fewer resources available for meeting task demands, a finding for which there is accumulative evidence (see Stout et al., 2013, 2014, Sari, Koster & Derakshan, 2016). As a consequence, worrying should be associated with compensatory cognitive effort which can be measured by the BOLD response in supplementary prefrontal areas of the brain. You attempt to test this hypothesis. You select three groups of participants randomly from the student population. You assign one group to a condition where they are encouraged to worry for 5 minutes about a pertinent concern, another group that is encouraged to think about the positive consequences of a near future event and a third group who is simply asked to do ‘nothing (or read)’! All participants complete an antisaccade task in an MRI scanner before and after the manipulation. You measure BOLD activity in microvolts. Conduct an appropriate ANOVA to understand the differential effects of your group manipulation on the BOLD response. The data is in the file: BOLD.sav. Now attempt the following: 1. Produce a graph that shows the BOLD response in each of your three groups before and after your manipulation. Comment on the pattern you see. [5 marks] 2. Does worrying result in a greater BOLD response in the prefrontal areas of the brain? a. Support your argument by stating the relevant main effect(s) and interaction effect of interest and a follow up Simple effects analysis that concentrates on group differences after the manipulation. [7 marks] b. Using the relevant formulae, calculate the model error (df), and the df for the explained variance in the interaction effect. Show how the F-value for the main effect of ‘Time’ and the interaction effect of ‘Time X Group’ is derived. [5 marks] c. Are you concerned about the main effect of Group? Perform a simple contrast analysis on Group to compare Worrying Bold responses against each of the other two conditions. Comment. [7 marks] Section C (26 marks) Go back to Q2 ? ! Assume you presented your amazing results in a conference where all the experts where enthusiastically listening to your speech! As it happens, a clever student from Birkbeck was in the audience. She raised a question that made you re-think your effects. This student questioned the possibility of a participant’s general level of working memory capacity (WMC) influencing the BOLD response obtained after the manipulation. This is a fair and valid comment, so you thank her and promise to re-examine your effects after covarying for the effects of WMC. So, go back to the datafile. Perform an appropriate analysis to covary for the effects of WMC that could possibly be influencing levels of BOLDafter responses. Attempt the following: 1. How do the pattern of means (adjusted for covariate) change after controlling for the possible effects of WMC on the BOLDafter response? Is WMC significantly influencing BOLDafter? How does the effect of Group on BOLDafter change when you partial out for WMC? How does the Worry group compare to the others after controlling for WMC? [10 marks] 2. Perform an appropriate analysis to test for the homogeneity of regression slopes assumption in this example. Have you met this assumption? Produce a graph to show the regression slopes for each group. [8 marks] 3. Calculate the effect size for the contrast looking at ‘worry’ vs ‘read’ and ‘worry’ vs ‘positive’. Comment on the amount of variation in BOLDafter explained by these contrasts. [8 marks]