A new rating scale for anxiety that is under evaluation has a sensitivity of 80% and specificity of 90% against the standard ICD-10 diagnosis.
Which one of the following is correct?
A. Sensitivity of a diagnostic test refers to the proportion of diseased subjects who have a positive test result (true positive rate). If it is 80%, then out of 10 truly diseased (anxious) people, eight will be correctly identified using the instrument. Specificity refers to the proportion of the non-diseased subjects who have a negative test result (true negative rate). So nine out of 10 people without anxiety will be correctly identified as ‘normal’ using the instrument. Choices D and E refer to positive and negative predictive values, respectively. Positive predictive value refers to the proportion of test-positive subjects who are actually diseased. For the given values of sensitivity and specificity this is 8/9. Negative predictive value refers to the proportion of test-negative subjects who are in fact ‘normal’. For the given values of sensitivity and specificity this is 2/11.
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Which of the following best describes a receiver–operator curve? It is often used to:
B. A receiver–operator curve is used to decide the optimal cut-off of a screening test. A funnel plot is used in systematic reviews and meta-analyses to demonstrate publication bias. The likelihood ratio of a negative result in diagnostic evaluation is given by a likelihood nomogram. The survival rates of inception cohorts in a follow-up study are demonstrated using a Kaplan–Meier curve. Kappa statistics can be used to test inter-rater reliability of a new instrument.
A pilot develops acute manic episode while flying with 200 passengers. After nearly 2 hours of struggle by the rest of the crew, the flight is fl own to safety. The 200 passengers are followed up for development of PTSD symptoms in the next 2 years. This study can be termed a:
B. Cohort studies can be differentiated from case–control studies on the basis of the time of exposure and duration of observation. In case–control studies the exposure has occurred in the past, unknown to the researcher. Cases and controls are independently recruited and differential exposure is ascertained in the two groups. In cohort studies, recruitment into a study takes place as soon as or as and when the exposure occurs (exposure cohort). In this question, exposure is the traumatic flight. Outcome is prospectively observed development of PTSD. Therefore this is a cohort study.
From a nationwide, cross-sectional survey it was found that 8% of otherwise normal children experience auditory hallucinations by the age of 11. This 8% of the survey sample was followed up annually for next 20 years to detect incidence of schizophrenia. This group can be termed a/an
A. Inception cohort refers to all individuals assembled at a given point based on some factor, for example common demography or common life experience. In the above example, following a survey, a group of individuals with similar experience of auditory hallucinations are followed up prospectively. Hence they constitute an inception cohort. Open cohort refers to recruiting the cohort over an extended period of time instead of choosing the same point in time. In most open cohorts the individual subjects are followed up for variable time intervals until the study is completed.
X is strongly associated with Y. A study investigates whether X causes Y. Which one of the following weakens the claim for a causal association between X and Y?
D. Widely known as the Bradford Hill’s criteria for causal association, demonstration of the following helps to ascertain cause–effect relationships:
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