12. A study aims to explore the factors associated with the risk of depression and anxiety in phaeochromocytoma patients. Depression of the patients is identied by was identied by the Hospital Anxiety and Depression Scale (HADS). HADS scores 0 21 in which 0 7 as normal and 7 or above as borderline or abnormal. The demographic variables include age and gender. Risk factors include tobacco and alcohol use. a. In the study, there are 131 patients diagnosed as depression and 63 not. Calculate the proportions of depression and the 95% condence interval for the proportion. b. Determine the sample size if the conservative margin of error for the proportion of patients having Hypertension is limited by :|:5.2%. 0. Consider a study of 400 patients. Briey describe how to conduct a retrospective survey to study the effects of the risk factors on depression among the patients. State how to analyses the effects of the risk factors on depression