mhgr {Hmisc}  R Documentation 
Miscellaneous Functions for Epidemiology
Description
The mhgr
function computes the CochranMantelHaenszel stratified
risk ratio and its confidence limits using the GreenlandRobins variance
estimator.
The lrcum
function takes the results of a series of 2x2 tables
representing the relationship between test positivity and diagnosis and
computes positive and negative likelihood ratios (with all their
deficiencies) and the variance of
their logarithms. Cumulative likelihood ratios and their confidence
intervals (assuming independence of tests) are computed, assuming a
string of all positive tests or a string of all negative tests. The
method of Simel et al as described in Altman et al is used.
Usage
mhgr(y, group, strata, conf.int = 0.95)
## S3 method for class 'mhgr'
print(x, ...)
lrcum(a, b, c, d, conf.int = 0.95)
## S3 method for class 'lrcum'
print(x, dec=3, ...)
Arguments
y 
a binary response variable 
group 
a variable with two unique values specifying comparison groups 
strata 
the stratification variable 
conf.int 
confidence level 
x 
an object created by 
a 
frequency of true positive tests 
b 
frequency of false positive tests 
c 
frequency of false negative tests 
d 
frequency of true negative tests 
dec 
number of places to the right of the decimal to print for

... 
addtitional arguments to be passed to other print functions 
Details
Uses equations 4 and 13 from Greenland and Robins.
Value
a list of class "mhgr"
or of class "lrcum"
.
Author(s)
Frank E Harrell Jr fh@fharrell.com
References
Greenland S, Robins JM (1985): Estimation of a common effect parameter from sparse followup data. Biometrics 41:5568.
Altman DG, Machin D, Bryant TN, Gardner MJ, Eds. (2000): Statistics with Confidence, 2nd Ed. Bristol: BMJ Books, 105110.
Simel DL, Samsa GP, Matchar DB (1991): Likelihood ratios with confidence: sample size estimation for diagnostic test studies. J Clin Epi 44:763770.
See Also
Examples
# Greate Migraine dataset used in Example 28.6 in the SAS PROC FREQ guide
d < expand.grid(response=c('Better','Same'),
treatment=c('Active','Placebo'),
sex=c('female','male'))
d$count < c(16, 11, 5, 20, 12, 16, 7, 19)
d
# Expand data frame to represent raw data
r < rep(1:8, d$count)
d < d[r,]
with(d, mhgr(response=='Better', treatment, sex))
# Discrete survival time example, to get CoxMantel relative risk and CL
# From Stokes ME, Davis CS, Koch GG, Categorical Data Analysis Using the
# SAS System, 2nd Edition, Sectino 17.3, p. 596599
#
# Input data in Table 17.5
d < expand.grid(treatment=c('A','P'), center=1:3)
d$healed2w < c(15,15,17,12, 7, 3)
d$healed4w < c(17,17,17,13,17,17)
d$notHealed4w < c( 2, 7,10,15,16,18)
d
# Reformat to the way most people would collect raw data
d1 < d[rep(1:6, d$healed2w),]
d1$time < '2'
d1$y < 1
d2 < d[rep(1:6, d$healed4w),]
d2$time < '4'
d2$y < 1
d3 < d[rep(1:6, d$notHealed4w),]
d3$time < '4'
d3$y < 0
d < rbind(d1, d2, d3)
d$healed2w < d$healed4w < d$notHealed4w < NULL
d
# Finally, duplicate appropriate observations to create 2 and 4week
# risk sets. Healed and not healed at 4w need to be in the 2week
# risk set as not healed
d2w < subset(d, time=='4')
d2w$time < '2'
d2w$y < 0
d24 < rbind(d, d2w)
with(d24, table(y, treatment, time, center))
# Matches Table 17.6
with(d24, mhgr(y, treatment, interaction(center, time, sep=';')))
# Get cumulative likelihood ratios and their 0.95 confidence intervals
# based on the following two tables
#
# Disease Disease
# +  + 
# Test + 39 3 20 5
# Test  21 17 22 15
lrcum(c(39,20), c(3,5), c(21,22), c(17,15))