Update docs/source/models/other_models/alzheimers_proportional_multistate_life_table/index.rst

Co-authored-by: Nathaniel Blair-Stahn <ndbs@uw.edu>

Author: SylLutze

docs/source/models/other_models/alzheimers_proportional_multistate_life_table/index.rst

@@ -264,7 +264,7 @@ On each time step, simulants in the negative test states are advanced to the nex
 
 A fraction of 
 incident 65 year olds that are selected for testing based on the current test rate. Additionally, a number :math:`U` of the untested state simualants are also
-selected for testing based on the increase in test rate compared to last year, :math:`\Delta_{\text{test_rates}}`:
+selected for testing based on the increase in test rate compared to last year, :math:`\Delta_{\text{test\_rates}}`:
 
 :math:`U = \Delta_{\text{test_rates}} * \text{total_age_pop}`, where :math:`\text{total_age_pop}` is the sum of all simulants 
 in the age/sex group (among all states- untested, positive and negative).