\title{studies on the effectiveness of warfarin for preventing strokes}
\description{results from 6 clinical trials examining the effectiveness of adjusted-dose warfarin for preventing strokes in patients with atrial fibrillation.}
\bold{trial}    \tab \code{numeric}   \tab trial number \cr
\bold{study}    \tab \code{character} \tab study name (abbreviated) \cr
\bold{x1i}      \tab \code{numeric}   \tab number of strokes in the warfarin group \cr
\bold{n1i}      \tab \code{numeric}   \tab number of patients in the warfarin group \cr
\bold{t1i}      \tab \code{numeric}   \tab total person-time (in years) in the warfarin group \cr
\bold{x2i}      \tab \code{numeric}   \tab number of strokes in the placebo/control group \cr
\bold{n2i}      \tab \code{numeric}   \tab number of patients in the placebo/control group \cr
\bold{t2i}      \tab \code{numeric}   \tab total person-time (in years) in the placebo/control group \cr
\bold{compgrp}  \tab \code{character} \tab type of comparison group (placebo or control) \cr
\bold{prevtype} \tab \code{character} \tab type of prevention (primary or secondary) \cr
\bold{trinr}    \tab \code{character} \tab target range for the international normalized ratio (inr)
the 6 studies provide data with respect to the number of strokes in the warfarin and the comparison (placebo or control) group. in addition, the number of patients and the total person-time (in years) is provided for the two groups. the goal of the meta-analysis was to examine the effectiveness of adjusted-dose warfarin for preventing strokes in patients with atrial fibrillation.
hart, r. g., benavente, o., mcbride, r., & pearce, l. a. (1999). antithrombotic therapy to prevent stroke in patients with atrial fibrillation: a meta-analysis. \emph{annals of internal medicine}, \bold{131}(7), 492--501. \verb{https://doi.org/10.7326/0003-4819-131-7-199910050-00003}
### calculate log incidence rate ratios and corresponding sampling variances
dat <- escalc(measure="irr", x1i=x1i, x2i=x2i, t1i=t1i, t2i=t2i, data=dat)
### meta-analysis of log incidence rate ratios using a random-effects model
### average incidence rate ratio with 95\% ci
ilab=cbind(paste(x1i, "/", t1i, sep=" "),
### meta-analysis of incidence rate differences using a random-effects model
res <- rma(measure="ird", x1i=x1i, x2i=x2i, t1i=t1i, t2i=t2i, data=dat)