Occupational injury and illness rates are used by employers and regulatory agencies to monitor the health and safety of workers. Changes in the rates are interpreted to reflect actions taken or not taken by the employer. The purpose of this study was to delineate external factors, those factors outside the control of employers, which influence occupational injury and illness rates. The results of this study are useful in interpreting changes in the occupational injury and illness rates as a function of changes in the external factors. A review of the literature provided information on the type of external forces which would be expected to influence occupational injury/illness rates. The factors selected for the data analysis included economic indicators, regulatory budget and performance measures, firm size, and leniency in workers' compensation claim determination as measured by the proportion of denied claims. Data were collected on the injury/illness incidence, lost workday case incidence, and lost workday rates for the state of Oregon for 1978 through 1987. Multiple linear regression models were constructed for each of the injury/illness rates using a step-down variable selection process to determine the predictor variables for each model. Separate models were constructed for each dependent variable using the values of the predictor variables for the same year and for the preceding year. The results supported the hypotheses that the unemployment rate, gross state product, number of serious violations cited by OSHA, and percentage of claims denied by the Workers' Compensation Board influence occupational injury and illness rates. Total OSHA expenditures and the number of inspections conducted by OSHA in a given year demonstrated positive relationships with lost workday cases incidence and injury/illness incidence rates, respectively; the positive associations were contrary to the hypothesized relationships. Models can be constructed using data on external factors to predict injury/illness incidence, lost workday case incidence, and lost workday rates. The unemployment rate was the most useful variable in predicting occupational injury and illness rates. / Graduation date: 1991