A statistical assessment of zero-polarization catalogues

The statistical bebaviour associated with polarization measurements is presented. The cumulative distribution function for measurements of unpolarized sources normalised by the measurement error is considered and Kolmogorov tests have been applied to data which might be considered as being representative of assemblies of unpolarized stars. Tinbergen's (1979, 1982) and Piirola's (1977) catalogues have been examined and reveal short-comings, the former indicating the presence of uncorrected instrumental polarization in part of the data and both suggesting that the quoted errors are in general slightly underestimated. Citings of these catalogues as providing evidence that middle-type stars in general exhibit weak intrinsic polarizations are shown to be invalid