For example, a paediatric registrar in a district general hospital is investigating the amount of lead in the urine of children from a nearby housing estate. To do this we need to abbreviate the observations to two significant digits. We first write the stems in order down the page. Thus, for the first data point, we write a 6 opposite the 0 stem. These are as given in Figure 1.1 .
Simple inspection can disclose irregularities.
Furthermore, a glance at the figures gives information on their range. The smallest value is 0.1 and the largest is 3.2 . For 15 points, the mid point is clearly the eighth largest, so that seven points are less than the median, and seven points are greater than it. This is easily obtained from Figure 1.2 by counting the eighth leaf, which is 1.5 . To find the median for an even number of points, the procedure is as follows.