Micro studies in the US find that part-time employees who prefer to work full-time (involuntary part-timers) are more likely to move to full-time employment than those who work part-time voluntarily. These findings are taken as evidence that the subjective classification of involuntary part-timers has a behavioral content. In contrast, the tendency of Israeli involuntary part-timers to move to full-time jobs is similar to that of voluntary ones. Nevertheless, we argue that the raw rate of transition is not a conclusive test and suggest an alternative one: observing the differences in the response of voluntary and involuntary part-timers to changes in labor demand. Using the repeated interviews in Israeli Labor Force Surveys, we create a dataset that covers the period 1991-2004 and find that GDP growth and changes in labor demand increase the probability that involuntary part-timers will move to full-time jobs, but have no effect on voluntary part-timers. Therefore, despite the virtually identical raw transition rates of voluntary and involuntary part-timers, this subjective classification appears to have a significant behavioral content.