Control variables
All the further analyses used the same set of control variables. The majority reflect
previous research concerning the determinants of unionisation: size, industry, ownership,
region, female and part-time proportions in the workforce, whether a single-site
organisation or part of a multi-site organisation, and time at the present location.
Other variables, not found in previous analyses of unionisation, concerned the number
of job levels, and the workplace’s opening days and opening hours: these have recently
been found to be significant influences on many aspects of employers’ workplace
practices (White
et al. , 2004).