Update readme

Author: Dominic Muston

README.md

@@ -54,10 +54,9 @@ Given this, the package enables:
   for each of the 3 model structures (given a time horizon), to evaluate
   plausibility and structural sensitivity. Additional functionality:
 
-  - Constraining the estimates to ensure that mortality survival is no greater than background mortality.
-  
+  - Constraining the estimates to ensure that mortality hazards are at
+    least as great as background morality.
   - Applying discounting to obtained discounted restricted means.
-  
   - Bootstrap standard errors can be derived.
 
 - Graphically illustrate observed and fitted membership probabilities,
@@ -81,7 +80,8 @@ be used for the one-piece parametric and spline modeling.
 A second vignette, `vignette("background-mortality")` illustrates how,
 after fitting models, estimates of restricted mean durations in health
 states can be calculated after constraining for background mortality
-from a given life table. Projected survival in the modeled dataset is assumed to be no greater than background survival.
+from a given life table. This mortality is assumed to add to the
+mortality hazard observed in the dataset.
 
 ## Installation
 
@@ -136,4 +136,3 @@ different licenses.
     application to prognostic modelling and estimation of treatment
     effects. Statistics in Medicine 21(1):2175-2197; 2002. [DOI:
     10.1002/sim.1203](https://doi.org/10.1002/sim.1203)
-