Dictionary of Evidence-based Medicine.pdf

34 Dictionary of Evidence-based Medicine
Nearly all theories in psychology refer to constructs rather than to specific
behaviours (Nunnally JC, Bernstein IH (1994) Psychometric theory. 3rd edn.
McGraw-Hill, New York). Anxiety and intelligence are examples of
constructs. We cannot measure these directly but have to use surrogate
measures such as the intelligence quotient (IQ) test, with all the associated
problems of validity which such an approach brings about.
Consumer surplus
Consumer surplus refers to the difference between what a consumer actually
pays for a good or service and the most that he or she would be willing
to pay.
Contestable market
A contestable market is one in which there are no entry and exit barriers.
Context effect
It is being increasingly recognized that patients' responses to treatments
may be affected by various factors such as how the investigator presents
the interventions. These non-specific effects are referred to as context
effects. To neutralize such effects, randomization, concealed assignment of
treatment and blinding are used in well-conducted trials. The term 'context
effect' has also been suggested as a better way of describing the 'placebo
effect', as the latter has derogatory connotations.
Contingency table
A contingency table is one in which subjects or objects from a group are
assigned to mutually exclusive categories or cells. In other words, each
individual is entered in one cell only. Each cell gives the total number (or
counts) of subjects or objects belonging to a subgroup. An example of a
contingency table is shown in Table 1.
Table I Contingency table showing hypothetical data from a comparative trial of three
drugs on mortality. Each arm of the study entered 100 patients
Drug Deaths Survived Total
Drug A
Drug B
Placebo
Total
5
20
40
65
95
80
60
235
100
100
100
300