diff --git a/R/define.R b/R/define.R
index f2935f0a..14ed6eb9 100644
--- a/R/define.R
+++ b/R/define.R
@@ -26,7 +26,7 @@
 #' \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 rate can be
+#' 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.
@@ -88,7 +88,7 @@ define_enroll_rate <- function(
 #' Define failure rate
 #'
 #' Define subject failure rate for a study with two treatment groups.
-#' Also supports stratified designs that have different failure rate in
+#' Also supports stratified designs that have different failure rates in
 #' each stratum.
 #'
 #' @details
@@ -99,8 +99,8 @@ define_enroll_rate <- function(
 #' The failure rate, dropout rate, and hazard ratio in a study duration
 #' can be specified.
 #'
-#' For a study with multiple strata, different duration, failure rate,
-#' dropout rate, and hazard ratio can be specified in each stratum.
+#' 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.
diff --git a/man/define_enroll_rate.Rd b/man/define_enroll_rate.Rd
index 50c827db..6c254adc 100644
--- a/man/define_enroll_rate.Rd
+++ b/man/define_enroll_rate.Rd
@@ -25,7 +25,7 @@ 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 rate can be
+For a study with multiple strata, different duration and rates can be
 specified in each stratum.
 }
 \examples{
diff --git a/man/define_fail_rate.Rd b/man/define_fail_rate.Rd
index 5740943a..162bce66 100644
--- a/man/define_fail_rate.Rd
+++ b/man/define_fail_rate.Rd
@@ -22,7 +22,7 @@ A \code{fail_rate} data frame.
 }
 \description{
 Define subject failure rate for a study with two treatment groups.
-Also supports stratified designs that have different failure rate in
+Also supports stratified designs that have different failure rates in
 each stratum.
 }
 \details{
@@ -33,8 +33,8 @@ The \code{duration} are ordered piecewise for a duration equal to
 The failure rate, dropout rate, and hazard ratio in a study duration
 can be specified.
 
-For a study with multiple strata, different duration, failure rate,
-dropout rate, and hazard ratio can be specified in each stratum.
+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