کلاسیک یا مونوپسونی جدید؟ جستجو برای شواهد در بازار کار پرستاری

The market for registered nurses (RNs) is often offered as an example of “classic” monopsony, while a “new” monopsony literature emphasizes that firm labor supply is upward sloping independent of market structure. Using data from multiple sources, we explore the relationship between nursing wages in hospitals and measures of classic and new monopsony. Wage level analysis fails to provide support for classic monopsony, the relative wages of RNs in 240 U.S. labor markets being largely uncorrelated with hospital system concentration. Longitudinal analysis shows nursing wages declining with increases in hospital concentration. We interpret these results as providing support for classic monopsony effects in the short run, but question whether wage effects are sustained in the long run. No relationship is found between nursing wages and a new monopsony measure of mobility, but support for new monopsony is found for women elsewhere in the labor market. RNs display greater inter-employer mobility than do women (or men) in general. Two conclusions follow. First, upward sloping labor supply need not imply monopsonistic outcomes. Second, absent more compelling evidence, nursing should not be held up as a prototypical example of monopsony—classic or new.

A common textbook example of monopsony is the market for registered nurses (RNs) employed in hospitals.2 The empirical literature, however, provides mixed conclusions. One strand focuses on empirical estimates of RN labor supply elasticities facing hospitals. This research is supportive of monopsony, in general finding upward sloping labor supply curves. A second strand investigates whether relative wage and/or employment outcomes vary with respect to hospital concentration, labor market size, and the like. Such studies provide little support for the classic monopsony model.3 These disparate results might be reconciled in several ways. One argument is that monopsony or oligopsony need not produce stable labor market outcomes; these may vary across time and with respect to market conditions. By this argument, one must search across different time periods and labor markets to determine the prevalence of oligopsonistic outcomes. A second argument is that monopsony is widespread, with employers in both concentrated and non-concentrated labor markets facing upward sloping firm-level supply curves owing to imperfect worker mobility (Manning, 2003). Following the argument of the “new monopsony” literature, market structure measures have limited relevance. Employers in large and small markets alike may face upward sloping supply curves and behave as oligopsonistic competitors. A third argument is that upward sloping labor supply is a necessary but not sufficient condition for monopsonistic outcomes (Hirsch and Schumacher, 1995). Although evidence may support existence of upward sloping supply facing individual employers, it need not follow that monopsonistic outcomes result.4 This paper addresses these contrasting views in an examination of wage determination in nursing labor markets. We provide tests of “classic” and “new” monopsony. The search for classic monopsony first examines whether relative wages of hospital RNs in urban markets is related to hospital system concentration and market size, the latter approximating the number of non-nursing and non-hospital nursing employers. We next examine whether changes in hospital concentration across markets lead to changes in relative RN wages, suggesting that this relationship represents a short-run but not necessarily long-run outcome. The search for new monopsony relies on a simple measure of oligopsonistic power proposed by Manning (2003)—the proportion of new hires from outside employment. If the proportion of new hires from employment (i.e., from other jobs) is high, the suggestion is that workers are mobile (an elastic firm-level labor supply) and monopsonistic power is weak. If new hires come primarily from outside employment (unemployment or out of the labor force), there may exist little mobility across employers. We calculate job transition rates for hospital RNs and a control group of female workers across urban labor markets.

Nursing is frequently proffered as an example of a monopsonistic labor market. This paper attempts to reconcile what has been rather mixed evidence on the topic. RNs and a control group of college-educated women are segmented into 240 urban and non-urban labor markets over the periods 1993–1997 and 1998–2002. Evidence consistent with classic monopsony is found using longitudinal analysis between the two periods, increases in hospital system concentration being associated with moderately lower RN wage growth and staffing ratios. Using wage level analysis, however, no evidence is found for higher relative nursing wages or staffing in larger markets or in markets with lower hospital concentration. For reasons stated earlier, our preferred interpretation is that the wage level analysis is likely to measure long-run outcomes. We conclude that short-run effects on wages and staffing from classic monopsony are unlikely to be sustained over time. Readers concerned that wage level results might be biased (toward zero) due to omitted fixed effects, however, might reasonably conclude that the longitudinal results reflect the long-run as well as short-run effects of classic monopsony. Little or no relationship is found across labor markets between RN wages and M, a mobility measure offered in the new monopsony literature as a proxy for the inverse supply elasticity. Values of M are substantially lower for hospital RNs than for women (or men) economy-wide, reflecting nursing skills that are readily transferable and the presence of multiple hospital and non-hospital employment options for RNs. We find a weak negative relationship between wages and M for the college-educated female control group, and a more substantial negative relationship between M and the wages of less-educated female workers. Because of data limitations, we were unable to provide longitudinal analysis relating wage changes to changes in M. Two principal conclusions follow from our analysis. First, evidence of upward sloping labor supply is not sufficient to infer monopsonistic outcomes. We do not dispute that workers are often immobile over the short and medium runs and that employers face upward sloping labor supply. It does not follow that differences in supply elasticities necessarily generate differences in wages. Before concluding that monopsony is important, one should measure outcomes. Second, whatever one thinks about the importance of monopsony, classic or new, the market for hospital RNs is a questionable example given the relatively high mobility of RNs across employers. Absent more compelling evidence of monopsonistic outcomes in nursing labor markets, economists should look elsewhere for a prototypical example of monopsony.