Most studies of what causes people to leave their current job (employee turnover) have focused exclusively on full-time employment. Much of this research draws attention to four categories of influence on turnover: work-related factors, such as low job satisfaction; external factors, such as wage-earner status in the household and attractive job alternatives; individual characteristics, such as education and age; and job performance (how well an individual functions in a particular job). A question that arises for industries that rely heavily on part-time labor is whether these factors influence turnover among part-time employees in the same manner that they do among full-time employees. Studies focusing on full-time employment have posited that the higher the employee's educational level, the higher that individual's expectations, leading to greater job dissatisfaction and increased likelihood of turnover. A recent study that focused on turnover among part-time workers suggests that when an individual assumes a part-time job as a secondary activity to supplement household income, it is probable that because of its lower importance, the job will cause considerably less frustration for the individual than will a job that provides a household's primary income. On the other hand, the same study finds support for applying to part-time workers the assertion found in full-time turnover literature that household primary-income earners are less likely than are other workers to leave a job voluntarily.
According to the passage, which of the following is true of the majority of studies of employee turnover?
They have focused primarily on turnover that is influenced by external factors.
They have shifted their emphasis in response to hiring trends in certain industries.
They have not examined differences in turnover between male and female employees.
They have not considered wage-earner status in the household as a factor in turnover.
They have not examined the reasons for turnover among part-time employees.