diff --git a/3_Epidemiology_Analysis/a_basics/1_basic_measures.ipynb b/3_Epidemiology_Analysis/a_basics/1_basic_measures.ipynb
index b7b8ed2..769a1a4 100644
--- a/3_Epidemiology_Analysis/a_basics/1_basic_measures.ipynb
+++ b/3_Epidemiology_Analysis/a_basics/1_basic_measures.ipynb
@@ -278,7 +278,7 @@
     "\n",
     "$$\\widehat{IRR} = \\frac{\\frac{a}{T_1}}{\\frac{b}{T_0}}$$\n",
     "\n",
-    "where $a$ is the number of individuals given ART and died, $T_1$ is the person-time contributed by individuals treated with ART, $b$ is the number of number of individuals not given ART and died, and $T_0$ is the person-time contributed by individuals treated with ART. The incidence rate ratio assumes that hazards follow an exponential distribution, meaning they are constant over time. This assumption may be more or less reasonable. If unreasonable, survival analysis methods like Kaplan-Meier, used be instead.\n",
+    "where $a$ is the number of individuals given ART and died, $T_1$ is the person-time contributed by individuals treated with ART, $b$ is the number of individuals not given ART and died, and $T_0$ is the person-time contributed by individuals not treated with ART. The incidence rate ratio assumes that hazards follow an exponential distribution, meaning they are constant over time. This assumption may be more or less reasonable. If unreasonable, survival analysis methods like Kaplan-Meier, used be instead.\n",
     "\n",
     "To calculate the incidence rate ratio, we use the following code"
    ]