The current retrospective study with descriptive-analytical design employed surgical interventions as output variable in the employed model, and the psychiatric hospital was excluded from the study due to lack of surgery ward. In addition, the two newly established Shaheed Rahimi and Shahid Valian hospitals in Aligudarz City were also excluded from the study due to lack of records in the defined period. Finally, all of the hospitals affiliated to Lorestan University of Medical Sciences (N = 12), except for the three abovementioned hospitals, were studied from 2010 to 2016. In order to observe ethical considerations, the results were provided with relevant numbers assigned to each hospital. The data and information required by the studied hospitals and the Treatment Department of Lorestan University of Medical Sciences were collected using a researcher-made checklist. According to previous studies, a combination of the most important and common inputs and outputs was selected to estimate the changes in total factor productivity. The data included inpatient and outpatient admissions, the number of surgeries, and bed occupancy rate as outputs, and the number of active beds, doctors, nurses, and other personnel as inputs (
18,
20-
23).
Data analysis was conducted in three phases as follows: in the 1st phase, after collecting data from the hospitals, the DEA method was employed to study hospitals from 2010 to 2016. There are several DEA models of which three classic models are extensively used to measure relative efficiency and productivity. The Malmquist index is one of the most significant models to measure and analyze five factors including total technical efficiency changes, technological efficiency changes, managerial efficiency changes (or pure technical efficiency), scale efficiency changes, and total factor productivity changes (ΔTFP) for hospitals based on DEA. The Malmquist productivity index is defined using distance functions as follows:
Where, , and are total factor productivity index, technological changes and efficiency changes, respectively. Distance function (Di) shows the relative distance of hospital from the efficient frontier. Output and input values in t and t+1 periods are shown with (qt, Xt) and (qt+1, Xt+1), respectively. The Malmquist index for the estimation of is:
Total productivity changes = Managerial efficiency changes × Scale efficiency changes technological changes
If the Malmquist index, with minimization of production factors assumption, is less than 1, it indicates better performance; but if the Malmquist index is greater than 1, it implies the performance worsening in the study period (
17).
The Deap 2.1 software was employed to measure the Malmquist productivity index.
Since DEA standard approach includes a relative measurement in which the efficiency and productivity scores of hospitals are calculated in comparison with those of the best hospitals in the model, there is always at least one hospital that achieves the performance score of 1 with 100% efficacy; and if the number of variables used to measure the relative efficiency of hospitals increases, the number of efficient hospitals also increases, which can lead to inability to identify hospitals with poor and good performances (
21). Therefore, the main DEA models, due to the lack of full ranking between the efficient units, do not support comparison between efficient units and, accordingly, the need to rank effective units is inevitable (
24,
25). In the 2nd phase, in order to rank the efficient hospitals, the Anderson-Peterson (AP) coefficient, which is a non-relative performance, was employed. Another approach to rank efficient hospitals noted in other studies was the evaluation of the number of referrals to each unit and assessing hospitals` positive/negative slacks to such an extent that hospitals with more referrals as well as the ones with negative slacks were more efficient, and there was usually a general agreement between this method and the AP coefficient to identify hospitals with super-efficiency (
21).
In the 3rd phase, the Kendrick-Creamer index was used to measure TFP. To calculate the index, the elasticity of total production with respect to the factors of production should be estimated and for this purpose, the production function should be estimated first. To estimate the production function, Frontier 4.1 software was employed, and accordingly, it was a Cobb-Douglas function. In this function, the coefficients of each of the production factors indicate its corresponding elasticity.
Function of production:
In this phase, using the elasticity of the production factors, the TFP of the studied hospitals were calculated with the Kendrick- Creamer index. The mathematical form of the Kendrick-Creamer function is as follows:
where TPi is the total productivity of hospital; Oi output, which in the current study was bed occupancy rate; P, the number of physicians; N, the number of nurses; B, the number of active beds; op, the number of other personnel; ep, elasticity of physicians; en, elasticity of nurses; eb, elasticity of active beds and eop, elasticity of other personnel in the studied hospitals.
Productivity growth, based on the Kendrick- Creamer index, was calculated using the following equation:
In the abovementioned equation, if all the production values are related to the physical quantity of the production factors, the equation value is zero, and the production growth is totally attributed to the growth of production factors. But if the value is positive, it indicates increased productivity in the studied hospitals (
4).
Finally, the marginal productivity of production factors; i.e., the amount of change in total production per unit of change in the application of the production factor, was estimated using the production function; and the elasticity obtained for the inputs was estimated by the following equations:
where Q/P is the minor (medium) productivity for the physician; Q/N, the minor productivity (medium) for the nurse; Q/B, the minor productivity (medium) for the active bed; Q/OP, the minor productivity (medium) for other personnel; α, the elasticity output with regards to the physicians; β, the elasticity output with regards to the nurses; γ, the elasticity output with regards to active beds, and ρ, the elasticity output with regards to other personnel.