Dictionary of Evidence-based Medicine.pdf

92 Dictionary of Evidence-based Medicine
Logic
Logic can be defined as the scientific evaluation of arguments where an
argument is a group of statements, one or more of which are put forward
to support one or more of the others. More succinctly, an argument is a
statement which includes a premise and a consequential conclusion. The
study of logic is aimed at developing the skills necessary for making sound
arguments and for critically assessing those of others (Hurley PJ (1994)
A concise introduction to logic. 5th edn. Wadsworth, Belmont, CA).
Logistic model
In many situations, we may wish to model the probability of a dichotomous
outcome (e.g. dead or alive) as a function of several variables. The
logistic model, denned by the equation below, is often useful.
f
1 +
where § is the probability of success for the zth group, a ; is a vector of
known constants, a' is the corresponding transpose and P is a vector of
unknown parameters which are to be estimated.
Logistic regression
A form of regression analysis used when the response (or dependent)
variable is a dichotomous (binary, yes/no) variable. Suppose that the
probability of an event which is dependent on a series of k variables (x or
predictor variables) is given by p, then logistic regression takes the form:
where the P values are unknown coefficients to be estimated in the
regression analysis.
Logistic transformation (see Logit)
Logit
Suppose that the probability of an event is p. The logit or logistic
transformation is given by log e /r^-\- Such a transformation is useful, for