R: Visual analog scale (VAS) data

vas5 {gamlss.data} | R Documentation

## 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)

### 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

    data(vas5)

[Package gamlss.data version 5.1-0 Index]