diff --git a/R/define.R b/R/define.R
index 6f5c12c3..14ed6eb9 100644
--- a/R/define.R
+++ b/R/define.R
@@ -18,7 +18,18 @@
 
 #' Define enrollment rate
 #'
-#' @param duration A numeric vector of piecewise study duration interval.
+#' Define the enrollment rate of subjects for a study as following a piecewise
+#' exponential distribution.
+#'
+#' @details
+#' The `duration` are ordered piecewise for a duration equal to
+#' \eqn{t_i - t_{i-1}}, where \eqn{0 = t_0 < t_i < \cdots < t_M = \infty}.
+#' The enrollment rates are defined in each duration with the same length.
+#'
+#' For a study with multiple strata, different duration and rates can be
+#' specified in each stratum.
+#'
+#' @param duration A numeric vector of ordered piecewise study duration interval.
 #' @param rate A numeric vector of enrollment rate in each `duration`.
 #' @param stratum A character vector of stratum name.
 #'
@@ -35,9 +46,9 @@
 #'
 #' # Define enroll rate with stratum
 #' define_enroll_rate(
-#'   stratum = c("low", "low", "high"),
-#'   duration = c(2, 2, 10),
-#'   rate = c(3, 6, 9)
+#'   duration = rep(c(2, 2, 2, 18), 3),
+#'   rate = c((1:4) / 3, (1:4) / 2, (1:4) / 6),
+#'   stratum = c(array("High", 4), array("Moderate", 4), array("Low", 4))
 #' )
 define_enroll_rate <- function(
     duration,
@@ -74,12 +85,27 @@ define_enroll_rate <- function(
   df
 }
 
-#' Define fail rate
+#' Define failure rate
+#'
+#' Define subject failure rate for a study with two treatment groups.
+#' Also supports stratified designs that have different failure rates in
+#' each stratum.
 #'
-#' @param duration A numeric vector of piecewise study duration interval.
-#' @param fail_rate A numeric vector of failure rate in each `duration`.
+#' @details
+#' Define the failure and dropout rate of subjects for a study as following
+#' a piecewise exponential distribution.
+#' The `duration` are ordered piecewise for a duration equal to
+#' \eqn{t_i - t_{i-1}}, where \eqn{0 = t_0 < t_i < \cdots < t_M = \infty}.
+#' The failure rate, dropout rate, and hazard ratio in a study duration
+#' can be specified.
+#'
+#' For a study with multiple strata, different duration, failure rates,
+#' dropout rates, and hazard ratios can be specified in each stratum.
+#'
+#' @param duration A numeric vector of ordered piecewise study duration interval.
+#' @param fail_rate A numeric vector of failure rate in each `duration` in the control group.
 #' @param dropout_rate A numeric vector of dropout rate in each `duration`.
-#' @param hr A numeric vector of hazard ratio.
+#' @param hr A numeric vector of hazard ratio between treatment and control group.
 #' @param stratum A character vector of stratum name.
 #'
 #' @return A `fail_rate` data frame.
@@ -87,7 +113,7 @@ define_enroll_rate <- function(
 #' @export
 #'
 #' @examples
-#' # Define enroll rate without stratum
+#' # Define enroll rate
 #' define_fail_rate(
 #'   duration = c(3, 100),
 #'   fail_rate = log(2) / c(9, 18),
@@ -97,11 +123,11 @@ define_enroll_rate <- function(
 #'
 #' # Define enroll rate with stratum
 #' define_fail_rate(
-#'   duration = c(3, 100),
-#'   fail_rate = log(2) / c(9, 18),
-#'   hr = c(.9, .6),
+#'   stratum = c(rep("Low", 2), rep("High", 2)),
+#'   duration = 1,
+#'   fail_rate = c(.1, .2, .3, .4),
 #'   dropout_rate = .001,
-#'   stratum = c("low", "high")
+#'   hr = c(.9, .75, .8, .6)
 #' )
 define_fail_rate <- function(
     duration,
diff --git a/man/define_enroll_rate.Rd b/man/define_enroll_rate.Rd
index 0893cd5f..6c254adc 100644
--- a/man/define_enroll_rate.Rd
+++ b/man/define_enroll_rate.Rd
@@ -7,7 +7,7 @@
 define_enroll_rate(duration, rate, stratum = "All")
 }
 \arguments{
-\item{duration}{A numeric vector of piecewise study duration interval.}
+\item{duration}{A numeric vector of ordered piecewise study duration interval.}
 
 \item{rate}{A numeric vector of enrollment rate in each \code{duration}.}
 
@@ -17,7 +17,16 @@ define_enroll_rate(duration, rate, stratum = "All")
 An \code{enroll_rate} data frame.
 }
 \description{
-Define enrollment rate
+Define the enrollment rate of subjects for a study as following a piecewise
+exponential distribution.
+}
+\details{
+The \code{duration} are ordered piecewise for a duration equal to
+\eqn{t_i - t_{i-1}}, where \eqn{0 = t_0 < t_i < \cdots < t_M = \infty}.
+The enrollment rates are defined in each duration with the same length.
+
+For a study with multiple strata, different duration and rates can be
+specified in each stratum.
 }
 \examples{
 # Define enroll rate without stratum
@@ -28,8 +37,8 @@ define_enroll_rate(
 
 # Define enroll rate with stratum
 define_enroll_rate(
-  stratum = c("low", "low", "high"),
-  duration = c(2, 2, 10),
-  rate = c(3, 6, 9)
+  duration = rep(c(2, 2, 2, 18), 3),
+  rate = c((1:4) / 3, (1:4) / 2, (1:4) / 6),
+  stratum = c(array("High", 4), array("Moderate", 4), array("Low", 4))
 )
 }
diff --git a/man/define_fail_rate.Rd b/man/define_fail_rate.Rd
index 906df3f4..162bce66 100644
--- a/man/define_fail_rate.Rd
+++ b/man/define_fail_rate.Rd
@@ -2,18 +2,18 @@
 % Please edit documentation in R/define.R
 \name{define_fail_rate}
 \alias{define_fail_rate}
-\title{Define fail rate}
+\title{Define failure rate}
 \usage{
 define_fail_rate(duration, fail_rate, dropout_rate, hr = 1, stratum = "All")
 }
 \arguments{
-\item{duration}{A numeric vector of piecewise study duration interval.}
+\item{duration}{A numeric vector of ordered piecewise study duration interval.}
 
-\item{fail_rate}{A numeric vector of failure rate in each \code{duration}.}
+\item{fail_rate}{A numeric vector of failure rate in each \code{duration} in the control group.}
 
 \item{dropout_rate}{A numeric vector of dropout rate in each \code{duration}.}
 
-\item{hr}{A numeric vector of hazard ratio.}
+\item{hr}{A numeric vector of hazard ratio between treatment and control group.}
 
 \item{stratum}{A character vector of stratum name.}
 }
@@ -21,10 +21,23 @@ define_fail_rate(duration, fail_rate, dropout_rate, hr = 1, stratum = "All")
 A \code{fail_rate} data frame.
 }
 \description{
-Define fail rate
+Define subject failure rate for a study with two treatment groups.
+Also supports stratified designs that have different failure rates in
+each stratum.
+}
+\details{
+Define the failure and dropout rate of subjects for a study as following
+a piecewise exponential distribution.
+The \code{duration} are ordered piecewise for a duration equal to
+\eqn{t_i - t_{i-1}}, where \eqn{0 = t_0 < t_i < \cdots < t_M = \infty}.
+The failure rate, dropout rate, and hazard ratio in a study duration
+can be specified.
+
+For a study with multiple strata, different duration, failure rates,
+dropout rates, and hazard ratios can be specified in each stratum.
 }
 \examples{
-# Define enroll rate without stratum
+# Define enroll rate
 define_fail_rate(
   duration = c(3, 100),
   fail_rate = log(2) / c(9, 18),
@@ -34,10 +47,10 @@ define_fail_rate(
 
 # Define enroll rate with stratum
 define_fail_rate(
-  duration = c(3, 100),
-  fail_rate = log(2) / c(9, 18),
-  hr = c(.9, .6),
+  stratum = c(rep("Low", 2), rep("High", 2)),
+  duration = 1,
+  fail_rate = c(.1, .2, .3, .4),
   dropout_rate = .001,
-  stratum = c("low", "high")
+  hr = c(.9, .75, .8, .6)
 )
 }