   ## Examples
 
       iex> run_times = [200, 400, 400, 400, 500, 500, 500, 700, 900]
-      iex> Benchee.Statistics.job_statistics(run_times, :run_time)
+      iex> Benchee.Statistics.job_statistics(run_times)
       %Benchee.Statistics{
         average:       500.0,
-        ips:           2000.0,
+        ips:           nil,
         std_dev:       200.0,
         std_dev_ratio: 0.4,
-        std_dev_ips:   800.0,
+        std_dev_ips:   nil,
         median:        500.0,
         percentiles:   %{50 => 500.0, 99 => 900.0},
         mode:          [500, 400],

            },
            memory_usage_statistics: %Benchee.Statistics{
              average:       500.0,
              ips:           0.0,
              std_dev:       200.0,
              std_dev_ratio: 0.4,
              std_dev_ips:   0.0,
              median:        500.0,
              percentiles:   %{50 => 500.0, 99 => 900.0},
              mode:          [500, 400],

        sample_size:   9
      }

      iex> Benchee.Statistics.job_statistics([100])
      %Benchee.Statistics{
        average:       100.0,
        ips:           nil,
        std_dev:       0,
        std_dev_ratio: 0.0,
        std_dev_ips:   nil,
        median:        100.0,
        percentiles:   %{50 => 100.0, 99 => 100.0},
        mode:          nil,
