  For each of the three indicators used, we have conducted a thorough error
analysis, and identified systematic errors in the computational procedures. For
the population ratio R = N_HB / N_RGB, we find that there is no evidence of a
trend with metallicity, although there appears to be real scatter in the values
derived. Although this indicator is the one best able to provide useful
absolute helium abundances, the mean value is Y approximately 0.20, indicating
the probable presence of additional systematic error.
  For the magnitude difference from the horizontal branch to the main sequence
Delta and the RR Lyrae mass-luminosity exponent A, it is only possible to
reliably determine relative helium abundances. This is due to continuing
uncertainties in the absolute metallicity scale for Delta, and uncertainty in
the RR Lyrae temperature scale for A. Both indicators imply that the helium
abundance is approximately constant as a function of [Fe/H]. According to the A
indicator, both Oosterhoff I and II group clusters have constant values
independent of [Fe/H] and horizontal branch type. In addition, the two groups
have slopes d log P / d[Fe/H] that are consistent with each other, but
significantly smaller than the slope for the combined sample.
