Added another exercies to section 4

Author: Christopher Fonnesbeck

4. Statistical Data Modeling.ipynb

@@ -1438,6 +1438,23 @@
      "metadata": {},
      "outputs": []
     },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "### Exercise: multivariate logistic regression\n",
+      "\n",
+      "Which other variables might be relevant for predicting the probability of surviving the Titanic? Generalize the model likelihood to include 2 or 3 other covariates from the dataset."
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [],
+     "language": "python",
+     "metadata": {},
+     "outputs": []
+    },
     {
      "cell_type": "markdown",
      "metadata": {},