Description

In the original data 368 patients, measured at 18 times after treatment with one of 7 drug treatments (including placebo), plus a baseline measure (time=0) and one or more pre-baseline measures (time=-1). Here for illustration we will ignore the repeated measure nature of the data and we shall use data from time 5 only (364 observations). The VAS scale response variable, Y, is assumed to be distributed as BEINF(mu,sigma,nu,tau) where any of the distributional parameters mu, sigma, nu and tau are modelled as a constant or as a function of the treatment,

Usage

Format

A data frame with 364 observations on the following 3 variables.

patient

a factor indicationg the patient

treat

the treatment factor with levels 1 2 3 4 5 6 7

vas

the response variable

Details

The Visual analog scale is used to measure pain and quality of life. For example patients are required to indicate in a scale from 0 to 100 the amount of discomfort they have. This can be easily translated to a value from 0 to 1 and consequently analyzed using the beta distribution. Unfortunately if 0's or 100's are recorded the beta distribution is not appropriate since the values 0 and 1 are not allowed in the definition of the beta distribution. Note that the inflated beta distribution allows values at 0 and 1. This is a mixed distribution (continuous and discrete) having four parameters, nu for modelling the probability at zero p(Y=0) relative to p(0<Y<1), tau for modelling the probability at one p(Y=1) relative to p(0<Y<1), and mu and sigma for modelling the between values, $0<Y<1$, using a beta distributed variable BE(mu,sigma) with mean mu and variance sigma*mu*(1-mu).

Source

The data were provided by Dr. Peter Lane

Examples