he difference between two potential outcomes. </td>
  </tr>
  <tr>
   <td style="text-align:left;"> introduction-7 </td>
   <td style="text-align:left;"> question </td>
   <td style="text-align:left;"> The fundamental problem of causal inference is that we can only observe one potential outcome. </td>
  </tr>
  <tr>
   <td style="text-align:left;"> introduction-8 </td>
   <td style="text-align:left;"> question </td>
   <td style="text-align:left;"> outcome variable is arrested </td>
  </tr>
  <t