NIOSH Publication No. 2004-146

Worker Health Chartbook 2004

Worker Health Chartbook > Appendix B > Survey of Occupational Injuries and Illnesses (SOII)

Appendix B

Survey of Occupational Injuries and Illnesses (SOII)

Survey Measures

The number of injuries and illnesses are reported nationwide and by industry for three basic types of cases:

Lost-workday cases
Cases involving days away from work
Nonfatal cases without lost workdays

Lost-workday cases may include (1) cases involving days away from work, or (2) cases involving restricted work activity only, or (3) both. For cases involving days away from work, the survey presents numeric and percent distributions by occupation and by the worker demographic traits and case characteristics, such as the part of body involved, the nature of the injury or illness, the source of the injury or illness, and the event or exposure in which the injury or illness was produced or inflicted. In addition, the survey includes two measures of severity for lost work-time cases: median number of workdays lost and a percent distribution of days-away-from-work cases by their duration. The latter measures are presented nationwide by industry and for the aforementioned worker and case characteristics.

In addition to injury and illness counts, the survey also reports on the frequency (incidence rate) of such cases. Incidence rates permit comparison among industries and establishments of varying sizes. They express various measures of injuries and illnesses in terms of a constant, i.e., exposure hours in the work environment (for example, 200,000 employee hours or the equivalent of 100 FTE employees working for 1 year), thus allowing for a common statistical base across industries regardless of employment size of establishments.

Incidence rates also are useful in evaluating the safety performance of an industry over time or in comparing State-to-State variations in an industry’s safety record. Such comparisons are possible using the total case rate or the rate for lost-workday cases, days-away-from-work cases, or nonfatal cases that do not involve lost workdays. These measures are available for injuries only and for injuries and illnesses combined. For illnesses, rates are available for total cases and separately for the seven illness categories (see Chapters 1 and 3). Rates for days-away-from-work injuries and illnesses are also available for the various categories of the four case characteristics studied, for example, the incidence rates associated with carpal tunnel syndrome, back cases, injuries inflicted by health care patients, or disabling falls to a lower level.

Incidence Rate Calculation

Incidence rates are calculated using the total obtained through BLS weighting and benchmarking procedures [BLS 2003]. The adjusted estimates for a particular characteristic, for example injury and illness cases involving days away from work, are aggregated to the appropriate level of industry detail. The total is multiplied by 200,000 (the base number of hours worked by 100 full-time employees for one year). The product is then divided by the weighted and benchmarked estimate of hours worked as reported in the survey for the industry segment.

The formula for calculating the incidence rate at the lowest level of industry detail is

Incidence rate =	(Sum of characteristic reported) • 200,000
	(Sum of the number of hours worked)

Incidence rates for higher levels of industry detail are produced using aggregated weighted and benchmarked totals. Rates may be computed by industry, employment size, geographic area, extent or outcome of case, and case characteristic category. Rates for illnesses and rates for case characteristic categories are published per 10,000 full-time employees using 20,000,000 hours instead of 200,000 hours in the formula shown above. Rates per 10,000 workers can be converted to rates per 100 workers by moving the decimal point left two places and rounding the resulting rate to the nearest tenth.

State Participation

Federal grants covering portions of the operating costs permit States to develop estimates of occupational injuries and illnesses and to provide the data from which BLS produces national results. National data for selected States that do not have operational grants are collected directly by BLS. The participating State agencies collect and process the data and prepare estimates using standardized procedures established by BLS to insure uniformity and consistency among the States. To further insure comparability and reliability, BLS designs and identifies the survey sample for each State. Through its regional offices, BLS validates the survey results and provides technical assistance to the State agencies on a continuing basis.

Publication Guidelines

The estimating procedure generates occupational injury and illness estimates for approximately 900 SIC codes. Industry estimates are not published if one of the following situations occurs:

Estimates for the industry are based on reports from fewer than three companies; the industry had fewer than six employees; or, if three or more companies report data for the industry, one firm employs more than 60% of the workers.
Average employment for the industry was fewer than 10,000 in the survey year. However, data for an industry with an annual average employment of less than 10,000 can be published if most of the employment was reported in the survey.
The relative standard error on total lost-workday cases for the industry exceeds a specified limit.
The benchmark factor for the industry is less than 0.90 or greater than 1.49.
Publication might disclose confidential information.

Data for an unpublished industry are included in the total for the broader industry level. In addition, selected items of data are suppressed for publishable industries if the sampling error for the estimate exceeds a specified limit, typically 60% at the national level.

For the case characteristics and demographic data, items of data are suppressed at the national level if one of the following situations occurred:

The number of cases is fewer than five.
The number of cases is greater than 5 and fewer than or equal to 20 and the sampling error for the estimate is greater than 60%.
The number of cases is greater than 20 and the sampling error is greater than 40%.

For further information, contact

U.S. Bureau of Labor Statistics
OCWC/OSH–Suite 3180
2 Massachusetts Avenue, NE
Washington, DC 20212–0001

Nonfatal summary information: 202–691–6179
Nonfatal case and demographic information: 202–691–6170
Fax: 202–691–6196
Nonfatal injuries and illnesses questions: oshstaff@bls.gov
www.bls.gov/iif/