  Asymmetric statistical errors arise for experimental results obtained by
Maximum Likelihood estimation, in cases where the number of results is finite
and the log likelihood function is not a symmetric parabola. This note
discusses how separate asymmetric errors on a single result should be combined,
and how several results with asymmetric errors should be combined to give an
overall measurement. In the process it considers several methods for
parametrising curves that are approximately parabolic.
