bj</th>
      <td><p>ggplot object</p></td>
    </tr>
    <tr>
      <th>pairs</th>
      <td><p>a list pairs of comparison. Groups indicated by integer numbers counted from left to right. e.g. list(c(1, 2), c(2, 3))
will compare first group with second, second group with third</p></td>
    </tr>
    <tr>
      <th>test</th>
      <td><p>character of statistical testing method. e.g. t.test, wilcox.test. Default wilcox.test</p></td>
    </tr>
    <tr>
      <th>heights</th>
      <td><p>integer or vector of 