The effectiveness of an intervention is measured by using pragmatic trials.
Which trial design is normally employed when carrying out a pragmatic trial?
A. RCTs provide high-quality evidence for or against proposed interventions. But RCTs have a major limitation in terms of generalizability. This is because the trials are conducted in a somewhat artificial experimental setting that is different from clinical practice. So RCTs have high internal validity due to rigorous methodology but poor external validity. Pragmatic RCTs are a type of RCTs introduced with the intention of increasing external validity, i.e. generalizability of RCT results. But this takes place at the expense of internal validity. In pragmatic RCTs the trial takes place in a setting as close as possible to natural clinical practice, i.e. the inclusion and exclusion criteria are less fastidious, often ‘treatment as usual’ is employed for comparisons, instead of placebos and real world, functionally significant outcomes are considered.
Reference:
The probability of detecting the magnitude of a treatment effect from a study when such an effect actually exists is called:
D. The power of a study refers to the ability of the study to show the difference in outcome between studied groups if such a difference actually exists. The term power calculation is often used while referring to sample size estimation before a study is undertaken. In order to carry out power calculation one has to know the expected precision and variance of measurements within the study sample (obtained from a literature search or pilot studies), the magnitude of a clinically significant difference, the certainty of avoiding type 1 error as reflected by the chosen p value, and the type of statistical test one will be performing. There is no point in calculating the statistical power once the results of a study are known. On completion of trials, measures such as confidence intervals indicate the power of a study and the precision of results.
Power is the ability of a study to detect an effect that truly exists.
Power can also be defined as:
E. Power refers to the probability of avoiding a type 2 error. To calculate power, one needs to know four variables:
Underpowered trials are those that enroll too few participants to identify differences between interventions (arbitrarily taken as at least 80% of the time) when such differences truly exist. Underpowered RCTs are prone to false-negative conclusions (type 2 errors). Somewhat controversially, underpowered trials are considered to be unethical, as they expose participants to the ordeals of research without providing an adequate contribution to clinical development.
A new diagnostic test detects 60 out of 100 schizophrenia patients correctly. It does not wrongly diagnose anyone in a sample of 100 controls.
The positive predictive value of this test is:
D. It is useful to construct a 2 × 2 table for calculating properties of reported diagnostic tests. From the given information we can draw the following:
Now, positive predictive value = true positive/total positive = 60/60 = 100%.
How sensitive is this test in detecting schizophrenia?
A.
Using the table above:
Sensitivity = true positive/total diseased (schizophrenia subjects) = 60/100 = 60%
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