gamlss.data (version 4.2-7)

vas5: Visual analog scale (VAS) data

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

data(vas5)

docType

data

source

The data were provided by Dr. Peter Lane

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(0tau for modelling the probability at one p(Y=1) relative to p(0mu and sigma for modelling the between values, $0BE(mu,sigma) with mean mu and variance sigma*mu*(1-mu).

Examples

data(vas5)