diff --git a/R/expected_event.R b/R/expected_event.R
index 223be66d..36b959f9 100644
--- a/R/expected_event.R
+++ b/R/expected_event.R
@@ -107,6 +107,22 @@
 #'   fail_rate = define_fail_rate(duration = 100, fail_rate = log(2) / 6, dropout_rate = .01),
 #'   total_duration = 22, simple = FALSE
 #' )
+#'
+#' # Single time period example, multiple strata
+#' enroll_rate <- define_enroll_rate(stratum = rep(c("Biomarker-positive", "Biomarker-negative"), each = 4),
+#'                                   duration = c(2, 2, 2, 6, 2, 2, 2, 6),
+#'                                   rate = c(1:4, 1:4))
+#' failure_rate <- define_fail_rate(stratum = rep(c("Biomarker-positive", "Biomarker-negative"), each = 2),
+#'                                  duration = c(3, 100, 3, 100),
+#'                                  fail_rate = log(2) / c(8, 12, 8, 10),
+#'                                  dropout_rate = 0.001)
+#' # Number of expected events by stratum
+#' sapply(c("Biomarker-positive", "Biomarker-negative"),
+#'        function(ss){
+#'          expected_event(enroll_rate = enroll_rate[enroll_rate$stratum == ss, ],
+#'                         fail_rate = failure_rate[failure_rate$stratum == ss, ],
+#'                         total_duration = 36,
+#'                         simple = TRUE)})
 expected_event <- function(
     enroll_rate = define_enroll_rate(
       duration = c(2, 2, 10),
@@ -120,6 +136,9 @@ expected_event <- function(
     total_duration = 25,
     simple = TRUE) {
 
+  # Report error where there is >=2 strata
+  if(length(unique(fail_rate$stratum)) >= 2 || length(unique(enroll_rate$stratum)) >= 2) {stop("Please calculate the expected event by stratum, see examples. ")}
+
   # Divide the time line into sub-intervals ----
 
   ## by piecewise enrollment rates
diff --git a/man/expected_event.Rd b/man/expected_event.Rd
index 5e6eaef3..a729d69a 100644
--- a/man/expected_event.Rd
+++ b/man/expected_event.Rd
@@ -112,4 +112,20 @@ expected_event(
   fail_rate = define_fail_rate(duration = 100, fail_rate = log(2) / 6, dropout_rate = .01),
   total_duration = 22, simple = FALSE
 )
+
+# Single time period example, multiple strata
+enroll_rate <- define_enroll_rate(stratum = rep(c("Biomarker-positive", "Biomarker-negative"), each = 4),
+                                  duration = c(2, 2, 2, 6, 2, 2, 2, 6),
+                                  rate = c(1:4, 1:4))
+failure_rate <- define_fail_rate(stratum = rep(c("Biomarker-positive", "Biomarker-negative"), each = 2),
+                                 duration = c(3, 100, 3, 100),
+                                 fail_rate = log(2) / c(8, 12, 8, 10),
+                                 dropout_rate = 0.001)
+# Number of expected events by stratum
+sapply(c("Biomarker-positive", "Biomarker-negative"),
+       function(ss){
+         expected_event(enroll_rate = enroll_rate[enroll_rate$stratum == ss, ],
+                        fail_rate = failure_rate[failure_rate$stratum == ss, ],
+                        total_duration = 36,
+                        simple = TRUE)})
 }