update model 2 wilkinson notation

Author: drbenvincent

examples/generalized_linear_models/GLM-simpsons-paradox.ipynb

@@ -949,9 +949,10 @@
    "metadata": {},
    "source": [
     ":::{note}\n",
-    "We can also express this Model 2 in Wilkinson notation as `y ~ g + x:g`.\n",
+    "We can also express this Model 2 in Wilkinson notation as `y ~ 0 + g + x:g`.\n",
     "\n",
     "* The `g` term captures the group specific intercept $\\beta_0[g_i]$ parameters.\n",
+    "* The `0` means we do not have a global intercept term, leaving the group specific intercepts to be the only intercepts.\n",
     "* The `x:g` term captures group specific slope $\\beta_1[g_i]$ parameters.\n",
     ":::"
    ]

examples/generalized_linear_models/GLM-simpsons-paradox.myst.md

@@ -288,9 +288,10 @@ Where $g_i$ is the group index for observation $i$. So the parameters $\beta_0$
 +++
 
 :::{note}
-We can also express this Model 2 in Wilkinson notation as `y ~ g + x:g`.
+We can also express this Model 2 in Wilkinson notation as `y ~ 0 + g + x:g`.
 
 * The `g` term captures the group specific intercept $\beta_0[g_i]$ parameters.
+* The `0` means we do not have a global intercept term, leaving the group specific intercepts to be the only intercepts.
 * The `x:g` term captures group specific slope $\beta_1[g_i]$ parameters.
 :::