minor edit

vignettes/mediation_analysis.Rmd

@@ -90,7 +90,8 @@ diagnosis <- diagnose_design( mediation_analysis_designer(rho = 0))
 kable(reshape_diagnosis(diagnosis)[, -c(1, 4:6, 13,14)], digits = 2)
 ```
 
-We can see that when the error terms of the mediator regression and the outcome regression are not correlated the direct and indirect effects can be estimated without bias. Unfortunately, the assumption of no correlation is not always guaranteed since $M$ is not assigned at random and can be correlated with $Y$.
+We can see that when the error terms of the mediator regression and the outcome regression are not correlated the direct and indirect effects can be estimated without bias. Unfortunately, the assumption of no correlation is not always guaranteed since $M$ is not assigned at random and might be correlated with $Y$.
+
 ### Using the Mediation Analysis Designer
 
 In R, you can generate a mediation_analysis design using the template function `mediation_analysis_designer()` in the `DesignLibrary` package by running the following lines, which install and load the package: