A 2 × 2 contingency table is constructed to analyze the primary outcome data of a trial.
The degrees of freedom to use chi-square statistics is:
A. ‘Degree of freedom’ is defined as the number of values in the final calculation of statistics that are free to vary. In a two-way chi-square test, this is given by Degrees of freedom (d.f.) = (number of rows – 1) × (number of columns – 1) In this question, for a 2 × 2 table, there are 2 rows and 2 columns.
Hence d.f. = (2 – 1) × (2 – 1) = 1 × 1 = 1. Degrees of freedom cannot take negative values.
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Which one of the following is correctly matched with the most suitable study method?
B. No single study design is sufficient in itself to answer various clinical questions. For evaluation of a diagnostic test, a survey design that allows comparison with the gold standard is often used.For prognostic studies a prospective cohort design is useful. Therapeutic interventions are best evaluated using RCTs. Aetiological studies are often cohort or case–control studies; although the RCT is ideal it may not be always possible to conduct one. Epidemiological studies are often cross-sectional surveys.
Which of the following characters of a pragmatic Randomized Controlled Trial (RCT) distinguishes it from an explanatory RCT?
D. The RCT has traditionally been considered as a study design that can yield results with a high degree of internal validity. But the major drawback of RCTs is that the process takes place under highly experimental conditions, which are not seen in clinical practice. So any results achieved from such RCTs, though valid, may not be reproducible in everyday practice. In order to circumvent this issue, more naturalistic trials that retain core principles of RCT such as randomization, longitudinal follow-up, and controlled intervention are being increasingly used. Such real-world RCTs are called pragmatic trials or effectiveness trials. Such trials can be useful to fi nd out if an intervention will be effective in clinical practice, although they may not be suitable to study the biological efficacy of a drug. A pragmatic RCT may reject various practices seen in an explanatory RCT, such as strict exclusion criteria, blinding, placebo use, fixed dose intervention, high follow-up care, per-protocol analysis, etc. But basic principles such as randomization and use of probability theory (hypothesis testing and p values) are retained.
Which one of the following statement with respect to bias is false?
C. Bias is defined as any trend in the collection, analysis, interpretation, publication,or review of data that can lead to conclusions that are systematically different from the truth. It can also be termed as a systematic error that influences the result in either direction. Hence a biased study could either overestimate or underestimate the true effect, depending on the direction of the trend. Bias may be introduced by poor study design or poor data collection.Bias cannot be ‘controlled for‘ at the analysis stage. In RCTs, randomization ensures a reduction in selection bias if the process is carried out in a strictly concealed manner. Blinding can reduce the measurement bias if properly executed.
Which one of the following is NOT a major disadvantage of a double blind, well-concealed RCT design?
E. Recall bias refers to the systematic error produced by the tendency of subjects to recall an exposure differently when they are diseased compared with when they are not. Recall bias most often occurs in case–control studies. The remaining choices refer to genuine disadvantages of a well-conducted RCT.
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