Firm, patient, and process variables associated with length of stay in four diseases

An application of mixture distributions in modelization of length of hospital stay

Length of hospital stay (LOS) is an important indicator of the hospital activity and management of health care. The skewness exhibited by this variable poses problems in statistical modeling. The aim of this work is to model the variable LOS within diagnosis-related groups (DRG) through finite mixtures of distributions. A mixture of the union of Gamma, Weibull and Lognormal families is used in the model, instead of a mixture of a unique distribution family. Some theoretical questions regarding the model, such as the identifiability and study of asymptotic properties of ML estimators, are analyzed. The EM algorithm is proposed for performing these estimators. Finally, this new proposed model is illustrated by using data from different DRGs.

Fitting the distributions of length of stay by parametric models

OBJECTIVES

The purpose of this study was to assess the adequacy of three widely used models--Lognormal, Weibull, and Gamma--for describing the distribution of length of stay. This is a fundamental step in the development of outliers resistant (robust) methods for the statistical analysis of this kind of data, where the main objective is to determine measures of average and total resource consumption of groups of patients. Current practice uses several types of trimming rules, many of which are based on the Lognormal model, although theoretical and experimental bases are still insufficient.

METHODS

The three models were adjusted using robust procedures based on M-estimators to approximately 5 million stays grouped by Diagnosis-Related Groups (DRGs). The resulting 3,279 samples were collected in five European countries during 3 years.

RESULTS

Most of the distributions observed could be fitted with one of these models. The descriptions provided by the Gamma and the Weibull models were similar, and the Gamma model could be omitted. The casemix description provided by the Log-normal-Weibull family was, for certain countries, significantly better than the one provided by the single Lognormal model. Often, for a given DRG and a given country, length of stay distributions could be described with the same model during several years. A given DRG, however, usually had to be described by means of different models for different countries.

CONCLUSIONS

Practical and conceptual consequences of the results are discussed. They can be extended to the analyses of other consumption variables used in health services. Statistical procedures for casemix description, including current rules of trimming, should be improved by means of more flexible families of models.

Why does length of stay vary for orthopaedic surgery?

This study examines the variation in length of stay in orthopaedic surgery in Grampian in 1988. It highlights the extent of variability across clinicians for patients with the same condition. The results indicate the importance of patient's age, type of admission and Diagnosis-Related Group. The inclusion of variables to identify the consultant in charge significantly improves the explanatory power of the model for all of the seven conditions investigated.

Variations in lengths of stay and rates of day case surgery: implications for the efficiency of surgical management

Variability in lengths of acute hospital stay and rates of day case surgery is shown to be a continuing pattern which occurs both between and within countries. A model of the determinants of health service activity is presented and the contribution of different factors to the observed variations is assessed. Differences in methods of funding health services are identified as a major determinant of the between country variations, while the within country variations largely reflect the influence of local differences in facilities and services and the organisation of care at a hospital level, as well as the independent effects of differences in clinical practice style. The main rationale for advocating a reduction in length of stay and increased use of day surgery is to increase efficiency by reducing costs per case while maintaining the quality of care. These criteria of costs, clinical outcomes and patient acceptability are examined in relation to day case surgery for an intermediate surgical procedure (inguinal hernia repair) and short stay surgery for cholecystectomy. The precise cost savings are shown to depend on the methods of costing, assumptions made and facilities employed, while factors influencing the outcomes achieved include the criteria of patient selection, the surgical techniques employed, and the adequacy of preoperative communication. Barriers to the more widespread adoption of short stay and day case surgery include practical and organisational constraints on clinical practice at a hospital level, lack of awareness among clinicians as to how far their practices differ from current norms, and clinical barriers raised by surgeons who do not see short stay policies as advantageous. Mechanisms to promote changes in clinical practice styles include independent professional audit, peer review, and involvement of clinicians in budgeting and resource allocation. Assessing quality requires that attention is given to patient acceptability and satisfaction as well as to the monitoring of clinical outcomes.

The management of acute cholecystitis and its hospital cost

This retrospective study compares the hospital costs of early and delayed cholecystectomy in the treatment of patients presenting with acute gallbladder disease. Of patients on the waiting list for delayed cholecystectomy, 27 per cent were readmitted as emergencies. The operating time was the same for early and delayed cholecystectomy. The overall average length of stay in the delayed group (16.1 days) was significantly greater (P < 0.001) than in the early group (12.4 days). The main difference in length of stay was due to the initial medical admission in the delayed group. The hospital costs, calculated on the basis of length of stay and hospital attendances, were pounds 156 cheaper (at 1977/78 prices) for early than for delayed cholecystectomy. Although the numbers were too small for valid statistical analysis, surgical outcome as measured by numbers of deaths, complications and readmissions was similar in the two groups. If more early cholecystectomies were performed, costs might be saved and surgical waiting lists reduced.