Did they explore control of extraneous variables?
Coyne: They concluded that size and ownership type make a difference in reported levels of efficiency. Not for profits seem to achieve higher performance levels, and medium and large not for profits operate more efficiently than industry average. The same results were found for cost levels, in that size and ownership type do make a difference, with medium sized hospitals reporting lower costs than large or small hospitals.
Yes, when they called for national studies that controlled for case mix, scope of services, and payer mix, all of which could have affected the results in this study in an unmeasured way.