Limited Intragenerational Mobility of Surgical Caseload of Iowa Hospitals.

We previously calculated the Gini index for 121 Iowa hospitals over the ten-year period 2007-2016. The Gini index is a statistic used in economics to assess difference in the distribution of wealth among groups. We reported a high degree of "inequality" among hospitals. In this paper, we extend this work by calculating the intragenerational mobility for the hospitals present in 2007-2008 and 2015-2016. Whereas in economics intragenerational mobility often is measured as changes in income over time within a group, we study changes in hospitals' surgical caseloads. Intragenerational mobility was quantified using the Spearman rank correlation, the slope of the ordinary least squares (OLS) regression line in the log scale, and the Shorrocks trace index. The results were consistent across the three measures. There was a low degree of mobility for the surgical caseloads of the hospitals during the 10-year period under study. For example, based on the slope of the OLS regression, intragenerational mobility was not significantly different from zero (P > 0.05). None (0%) of the 113 hospitals with at least 10 cases both periods increased from the 1st to 5th quintile, 1st to 4th quintile, 2nd to 5th quintile, 2nd to 4th quintile, or even from 3rd to 5th quintile. The results show the importance of hospitals not investing irrationally based on false hope of surgical growth.