Dictionary of Evidence-based Medicine.pdf

104 Dictionary of Evidence-based Medicine
ABSTINENCE
BrThorSoc(1983)
BrThorSoc(1983)
Russell (1983)
Russell (1983)
Fagerstrom (1984)
Hjalmarson (1984)
Killen (1984)
Clavel (1985)
Hall (1985)
Campbell (1987)
Campbell (1987)
Sutton (1987)
Harackiewicz (1988)
Llvina (1988)
Sutton (1988)
Tonnesen(1988b)
Blondal (1989)
Gilbert (1989)
Hughes (1989)
Campbell (1991)
Segnan(1991)
Pirie (1992)
Pirie (1992)
Zeiman (1992)
Herrera(1995)
TOTAL
POINT
PREVALENCE
Fee (1982)
Jarvis (1982)
Schneider (1983)
Jarvik(1984)
Hall (1987)
Tonnesen (1988a)
Killen (1990)
Killen (1990)
Richmond (1990)
McGovern (1992)
Nebot(1992)
Niaura(1994)
Fortmann (1995)
TOTAL
Figure 17 Meta-analysis: Comparison of conventional meta-analysis (left) and cumulative
meta-analysis (right) of nicotine chewing gum in smoking cessation at 12 months. Odds
ratios and associated 95% confidence intervals are shown
Model assessment
Model assessment refers to the validation of a mathematical model, in
which the focus is on how well the model predicts the observations rather
than how well it fits the data. In such an assessment, it is usual to replicate
design points to estimate pure error and then estimate lack of fit by adding
additional design points within the domain of the predictor (X) variables.
Consider a simple straight line model of the form Y = a X + b where Y is
the response variable and a and b are the intercept and slope respectively.
In estimating the coefficients of the model, Y values will be obtained for
various X values. Replicates (repeat observations of Y at the same X value)
are obtained to estimate the pure error. Y values corresponding to new X
values, within the domain of the original X values, are obtained to test for
lack of fit.