schizophrenia: National Institute of Mental Health Schizophrenia...

In mixor: Mixed-Effects Ordinal Regression Analysis

Description

In the NIMH Schizophrenia Collaborative Study, patients were randomized to receive one of four medications, either placebo or one of three different anti-psychotic drugs. The protocol indicated subjects were to then be evaluated at weeks 0, 1, 3, 6 to assess severity of illness; additionally some measurements were made at weeks 2, 4, and 5.

Usage

data(schizophrenia)

Format

A data frame with 1603 observations on the following 9 variables.

id

a numeric vector indicating the unique patient identifier

imps79

a numeric vector from item 79 on the Inpatient Multidimensional Psychiatric Scale indicating severity of illness. The scores were applied to be interpreted as follows: 1 = normal, not ill at all; 2 = borderline mentally ill; 3 = mildly ill; 4 = moderately ill; 5 = markedly ill; 6 = severly ill; 7 = among the most extremely ill

imps79b

a binary version of imps79

imps79o

an ordinally scaled version of imps79

int

a numeric vector of ones; used in stand-alone package to indicate intercept

TxDrug

a numeric vector indicating treatment with drug (1) or placebo (0)

Week

a numeric vector indicating time, in weeks

SqrtWeek

the square root of the Week variable

TxSWeek

a variable representing the TxDrug x Week interaction

Source

From http://tigger.uic.edu/~hedeker/SCHIZX1.DAT.txt

References

Hedeker D. and Gibbons R.D. (1996) A computer program for mixed-effects ordinal regression analysis. Computer Methods and Programs in Biomedicine 49, 157-176. Hedeker D and Gibbons R.D. (2006) Longitudinal Data Analysis, Wiley, Hoboken, New Jesery.

Examples

library("mixor")
data("schizophrenia")
### Random intercept
SCHIZO1.fit<-mixor(imps79o ~ TxDrug + SqrtWeek + TxSWeek, data=schizophrenia, 
     id=id, link="probit")
summary(SCHIZO1.fit)
### Random intercept and slope	
SCHIZO2.fit<-mixor(imps79o ~ TxDrug + SqrtWeek + TxSWeek, data=schizophrenia, 
     id=id, which.random.slope=2, link="probit")
summary(SCHIZO2.fit)
# random intercept and trend with independent random effects; using logit link
SCHIZO3.fit<-mixor(imps79o ~ TxDrug + SqrtWeek + TxSWeek, data=schizophrenia, 
     id=id, which.random.slope=2, indep.re=TRUE, link="logit")
summary(SCHIZO3.fit)

Example output

Loading required package: survival

Call:
mixor(formula = imps79o ~ TxDrug + SqrtWeek + TxSWeek, data = schizophrenia, 
    id = id, link = "probit")

Deviance =         3399.475 
Log-likelihood =  -1699.737 
RIDGEMAX =         0.2 
AIC =             -1706.737 
SBC =             -1721.017 

                    Estimate Std. Error z value   P(>|z|)    
(Intercept)         3.366361   0.186700 18.0308 < 2.2e-16 ***
TxDrug             -0.051665   0.177811 -0.2906    0.7714    
SqrtWeek           -0.459124   0.067960 -6.7558 1.420e-11 ***
TxSWeek            -0.672261   0.074807 -8.9866 < 2.2e-16 ***
Random.(Intercept)  1.227397   0.155361  7.9003 2.887e-15 ***
Threshold2          1.729302   0.070308 24.5963 < 2.2e-16 ***
Threshold3          2.939707   0.089910 32.6960 < 2.2e-16 ***
---
Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1

Call:
mixor(formula = imps79o ~ TxDrug + SqrtWeek + TxSWeek, data = schizophrenia, 
    id = id, which.random.slope = 2, link = "probit")

Deviance =         3327.048 
Log-likelihood =  -1663.524 
RIDGEMAX =         0 
AIC =             -1672.524 
SBC =             -1690.884 

                         Estimate Std. Error z value   P(>|z|)    
(Intercept)              4.101157   0.250907 16.3453 < 2.2e-16 ***
SqrtWeek                -0.505920   0.129339 -3.9116 9.169e-05 ***
TxDrug                   0.032407   0.222863  0.1454   0.88438    
TxSWeek                 -0.942635   0.147621 -6.3855 1.708e-10 ***
(Intercept) (Intercept)  2.171988   0.415157  5.2317 1.679e-07 ***
(Intercept) SqrtWeek    -0.452598   0.164452 -2.7522   0.00592 ** 
SqrtWeek SqrtWeek        0.619333   0.138302  4.4781 7.531e-06 ***
Threshold2               2.179066   0.109954 19.8179 < 2.2e-16 ***
Threshold3               3.643421   0.144105 25.2831 < 2.2e-16 ***
---
Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1

Call:
mixor(formula = imps79o ~ TxDrug + SqrtWeek + TxSWeek, data = schizophrenia, 
    id = id, which.random.slope = 2, link = "logit", indep.re = TRUE)

Deviance =         3338.65 
Log-likelihood =  -1669.325 
RIDGEMAX =         0 
AIC =             -1677.325 
SBC =             -1693.645 

                   Estimate Std. Error z value   P(>|z|)    
(Intercept)         6.79432    0.40000 16.9858 < 2.2e-16 ***
SqrtWeek           -0.69872    0.19527 -3.5783 0.0003459 ***
TxDrug              0.08664    0.31505  0.2750 0.7833147    
TxSWeek            -1.66334    0.22432 -7.4151 1.215e-13 ***
Random.(Intercept)  4.10323    0.73666  5.5700 2.547e-08 ***
Random.SqrtWeek     1.24592    0.27490  4.5323 5.834e-06 ***
Threshold2          3.77717    0.20157 18.7386 < 2.2e-16 ***
Threshold3          6.19845    0.26300 23.5680 < 2.2e-16 ***
---
Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1

mixor documentation built on May 2, 2019, 5:56 a.m.