fix grammatical error

Author: drbenvincent

docs/source/notebooks/did_pymc_banks.ipynb

@@ -835,7 +835,7 @@
     "\n",
     "The TWFE model is equivalent to the classic 2$\\times$2 DiD model (Model 1) - but only in the situation of two groups and two time periods. Outside of this special case the approach is not equivalent and can potentially have some problems {cite:p}`imai2021twfepanel`. Readers should proceed with caution when using the TWFE model outside of the 2$\\times$2 case - see for example{cite:p}`kropko2018two,collischon2020let`.\n",
     "\n",
-    "The TWFE approach similar to the previous model in that the `district:post_treatment` interaction term still gives you a treatment indicator variable and the assiated coefficient $\\beta_{\\Delta}$ is the causal effect of the intervention. But it is different in that there is no _linear_ `year` term, instead we have a _categorical_ `year` variable. This means that the model can capture any temporal trends in the data. These can be thought of as capturing time based schocks that affect all units.\n",
+    "The TWFE approach is similar to the previous model in that the `district:post_treatment` interaction term still gives you a treatment indicator variable and the assiated coefficient $\\beta_{\\Delta}$ is the causal effect of the intervention. But it is different in that there is no _linear_ `year` term, instead we have a _categorical_ `year` variable. This means that the model can capture any temporal trends in the data. These can be thought of as capturing time based schocks that affect all units.\n",
     "\n",
     "The equation for the expected values is:\n",
     "\n",