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Work-RISQS Technical Information


Data source Sample design Case definition Case exclusions Case identification
Injury estimates Rate estimates Injury estimate confidence bounds Injury rate confidence bounds Worker population
Treatment year Treatment month Age group Sex Race/ethnicity
Diagnosis Part of body ED disposition Event or exposure Source of injury/illness
Secondary source of
Data reports Minimum reporting


Back To Top Data source

Work-RISQS is an online data access system for NIOSH surveillance data on nonfatal work-related injuries and illnesses treated in U.S. hospital emergency departments (EDs). NIOSH collaborates with U.S. Consumer Product Safety Commission (CPSC) to collect these data through a supplement to the CPSC National Electronic Injury Surveillance System (NEISS). The occupational supplement is referred to as NEISS-Work. The occupational injury and illness supplemental data are collected without regard to consumer product involvement, whereas the CPSC NEISS data exclude work-related injuries and illnesses.

Back To Top Sample design

NEISS-Work is a national stratified probability sample of hospitals in the U.S. and its territories that have a minimum of six beds and that operate a 24-hour emergency department. Hospitals in the sample were selected from the approximately 5,300 rural and urban U.S. hospitals after stratification by total annual emergency department visits. Nominally, 67 geographically distributed sample hospitals capture work-related injuries and illnesses every day of the year (note: the occupational injury hospital sample is a subset (2/3) of the hospital sample used by CPSC for capture of product-related injuries). All treated cases that are identifiable as work-related are captured and information is abstracted from the medical record.

Each case is assigned a statistical weight based on the inverse probability of selection. National estimates are obtained by summing weights for all cases or particular cases of interest. Statistical weights are adjusted within a sample year to account for hospital mergers, hospital closings or withdrawal from NEISS-Work (i.e., less than 67 hospitals reporting information), and incomplete reporting. Statistical weights are adjusted annually based on the number of U.S. hospitals and their total number of ED visits as determined by a census of U.S. hospitals one year prior to the data year.

Back To Top Case definition

  • Nonfatal injuries and illnesses treated in an emergency department
  • Civilian non-institutionalized workers
  • Doing work for pay or other compensation, including arriving or leaving work but on the employer's premises, during transportation between locations as a part of the job (excluding commuting to or from home)
  • Doing agricultural production activities
  • Working as a volunteer for an organized group (e.g., volunteer fire department)
             More detailed guidelines...
  • All workers without restriction by age, type of employer or industry (e.g., self-employed, private industry, or government), or employer size

Back To Top Case exclusions

  • Injuries or illnesses to active duty Military, National Guard, and State Militia
  • Injuries or illnesses to institutionalized persons including prisoners or mental health patients
  • Common illnesses (e.g., colds and flu)
  • Routine drug and alcohol screening
  • Revisits to the same ED for a previously treated injury or illness

Back To Top Case identification

Work-related cases are identified from admissions information and emergency department chart review by hospital coders. A workers' compensation claim is not required for inclusion.


Back To Top Injury/illness estimates

NEISS-Work is designed to produce national estimates and is not suitable for regional, state, or local injury and illness estimates. A national estimate is obtained by extrapolating the number of cases seen in the approximately 67 hospitals by using the statistical weight of each case. The statistical weight varies depending upon the size of the hospital and the number of patients typically treated in their ED. In other words, each case captured in a sample hospital may represent 20 to more than 100 cases seen in other U.S. hospitals. By summing the weights for similar cases a national estimate is obtained for a specific demographic group, type of injury, injury circumstances, or all injuries and illnesses. In Work-RISQS, national estimates are expressed in thousands of injuries and illnesses for a given year. For example, in 1998 there were an estimated 3,559.5 thousand or 3,559,500 occupational injuries and illnesses treated in U.S. hospital emergency departments. Other surveillance systems may produce different estimates.

Back To Top Injury/illness estimate confidence bounds

Because the NEISS-Work system is just a sample of all U.S. hospitals and does not count every injury or illness treated in all hospitals, the national estimates may be in error. However, because the sample was statistically selected, we can calculate what the error due to sampling is likely to be. Each estimate produced by Work-RISQS has confidence bounds listed. The error estimates are based on the 95% confidence interval and are expressed as a value that should be subtracted from the estimate to get the lower confidence bound and added to it to get the upper bound. For example, in 1998, there were an estimated 3,559.5 thousand work-related injuries and illnesses with 95% confidence bounds of 605.1 thousand cases. In other words, we expect the true value from this system is likely to be in the range of 2,954,400 to 4,173,600 injuries and illnesses. Simply put--there were about three to four million non-fatal occupational injuries and illnesses treated in U.S. ED's in 1998.

The confidence bounds do not account for biases (nonsampling error) in the estimates that arise from the way in which data are collected or defined, ability to identify all work-related cases, or mistakes in data collection or coding.

The 95% confidence bounds are an approximation based on the classical formula for variance of a total from a stratified sample. These confidence bounds are an approximation of the general magnitude of error about an estimate and are not precise values.

The variance estimating formula currently used by Work-RISQS is:

Equation for the estimated variance, (sigma sub x)squared, of a stratified sample

m = Number of strata in the sample during the given time period
N sub h = Number of hospitals in the sampling frame for stratum h
n sub h = Number of hospitals selected for the sample for stratum h
n prime sub h = Number of in-scope hospitals in the sample for stratum h
r sub h = Number of hospitals participating in stratum h for the given time period
x sub hi = Number of occupational cases for a specific type of injury reported by hospital i in stratum h for the given time period
wgt sub hi = Weight of hospital i in stratum h
Equation for the average number of cases per hospital (x bar sub h) in stratum h Equation for the average total weight of cases per hospital in stratum h

The 95% confidence bounds, expressed as an amount to be subtracted or added to the national estimate, are then calculated as:

Confidence bounds = plus or minus the square root ((sigma sub x)squared) * 1.96
(sigma sub x)squared = Variance of the injury estimate x
x = Injury estimate
Effective with the December 2008 update to Work-RISQS a minor modification was made to the variance calculation in the way that the number of reporting hospitals was determined (r sub h) for all data years. Previously, hospitals were included in r sub h (an integer value) if the hospital reported for 7 or more months of the calendar period. To minimize issues with negative variances, r sub h is currently calculated as a fractional r sub h value where r sub h equals the sum of number of months that all hospitals within a strata reported during the calendar period divided by 12 months. Thus, current confidence bounds may not equal previously reported results, but the differences will generally be insignificant or undetectable.

Back To Top Worker population

The employment estimates used in Work-RISQS are derived from the U.S. Bureau of Labor Statistics Current Population Survey (CPS) of civilian non-institutionalized workers. Employment estimates are calculated for Work-RISQS as full-time equivalent workers (FTE), where one FTE equals 2,000 hours worked per year. The FTE estimates account for hours worked in all jobs reported to CPS. At Work-RISQS, FTE estimates may be obtained by month, quarter, or year for workers 15 years and older. Also, FTE estimates may be obtained by age group or sex.

Volunteer workers are not included in CPS estimates, although they are included in the Work-RISQS injury/illness counts. This creates a small, but insignificant, bias in rate estimates.

Approximate standard errors are calculated for CPS employment estimates by using parameters for selected demographic characteristics in a generalized variance function provided by the Bureau of Labor Statistics (see for example, USDOL Bureau of Labor Statistics Employment and Earnings Online, 2008: v. 55(1), 274-294). Parameters are independent of the time period selected within a given year, although they may change from year to year. In the calculation of error in the employment estimate, the selection of the variance parameters for the specific year are chosen based on the appropriate employment characteristics. When multiple characteristics apply for specific subsets of sex and/or age groups, the parameters are chosen to provide the most conservative error estimate (i.e., the largest error estimate). The errors generally decrease with longer time periods and when a specific sex or age group < 20 yrs is selected. However, the errors resulting from these calculations are only an approximation of the true sampling error and do not account for systematic biases in the data.

Back To Top Injury/illness rate estimates

In workplace safety, the injury/illness rate is calculated commonly as the frequency of injuries divided by the number of workers or the number of hours worked within a specific time period. Work-RISQS only provides rates as the number of injuries and illnesses per 200,000 hours worked (i.e., 100 FTE) for time periods of a month, quarter, or year. A rate estimate query at Work-RISQS produces a table that includes the number of injuries and illnesses treated in an ED (the rate numerator) , the FTE (the rate denominator), the rate per 100 FTE, and the confidence bounds expressed as a value to be added and subtracted from the rate value.

Back To Top Injury/illness rate confidence bounds

The variance of the rate estimate is the pooling of the variances for the injury estimate and the FTE estimate. In general, the variance about the injury estimate is large with respect to the variance in the FTE estimate. The confidence bounds, expressed as an amount to be subtracted or added to the injury/illness rate, are:

Confidence bounds = plus or minus the rate x (square root ((cv sub x)squared + (cv sub FTE)squared)) x 1.96


R sub FTE = Rate of injury/illness per 100 FTE
(cv sub x) squared = Coefficient of variation of the injury/illness estimate
(cv sub FTE) squared = Coefficient of variation of the employment FTE estimate


Back To Top Treatment year

Definition: Calendar year in which first emergency department medical treatment was received.

Injuries and illnesses in Work-RISQS may be queried based on the date of first treatment in a NEISS-Work hospital ED. The user may select data to query for one calendar year at a time, beginning in 1998. Multiple years can not be queried simultaneously within Work-RISQS.

Back To Top Treatment month

Definition: Calendar month in which first emergency department medical treatment was received.

Queries may be made for cases treated in one or more months. The months need not be consecutive. Injury estimates are based on the actual number of cases treated within a calendar month. In the determination of injury rates, the numerator is also based on the number of injuries treated within a calendar month. However, the FTE denominator assumes that all months have 30 days.

Back To Top Age group

Definition: Inclusive range of ages of patients (in years)

Injured or ill workers are grouped by age ranges (typically a 5 year range). One or more age groups may be selected. There are no age restrictions for cases captured in NEISS-Work providing they meet the definition of a work-related case. However, injury rates are not available for youth less than 15 years of age because data on hours worked are not available. Age is unknown for a small proportion of cases.

Back To Top Sex

Definition: The distinction between male and female.

A worker's sex is indicated as male, female, or not stated. In any given year's data, the number of cases with sex listed as not stated is very small (e.g., typically < 0.01% of all cases).

Back To Top Race/ethnicity

Definition: Construct for classifying people with similar biological, social, and cultural heritage into four race groups (White, Black, American Indian/Alaska Native, and Asian/Pacific Islander) and one ethnicity group (Hispanic or Latino) as recorded on the emergency department chart.

Within the original NEISS-Work data, race and ethnicity of an injured worker are collected as a two-part question. In the first part, race is coded as "white," "black," "other," or "not stated." In the second part which is free text, other races may be described such as Asian or American Indian or ethnicity may be entered such as Hispanic or Latino. Because NEISS-Work hospitals do not collect race and ethnicity uniformly, if they collect or report it at all, and the two-part nature of the NEISS-Work race/ethnicity question, consistent reporting of race and ethnicity is not always achieved. For example, a Hispanic patient might be indicated as: (1) white or black with the free text blank (only race reported); (2) white or black with Hispanic entered into the free text (both race and ethnicity reported); and (3) as "other" with Hispanic in the free text field (only ethnicity reported).

Within Work-RISQS, race and ethnicity were recoded under a single combined data structure where Hispanic ethnicity was indicated preferentially as opposed to white or black race. Thus, for the purposes of estimating injuries and illnesses, workers who were identified as white or black and Hispanic or Latino were counted under their Hispanic ethnicity. If originally race was listed as "other" and the free text contained a country of origin or ancestry, those cases were recoded to the race or ethnicity category predominant for the region (e.g., Chinese was recoded as Asian and Mexican was recoded as Hispanic). Race was recoded as "not stated" if the free text listed "Indian" without an indication that the patient was American Indian or Native American. However, Indian was recoded to American Indian if the NEISS-Work hospital where the case was seen generally treated a large population of American Indians.

WARNING: Because of the problems outlined and others in the collection of race and ethnicity information as well as missing information for approximately 20% of cases, Work-RISQS estimates for specific race or Hispanic worker populations should be used with caution.

Back To Top Diagnosis

Definition: The nature of the most severe injury or illness as described by the attending physician or other medical staff. If a medical diagnosis is missing from the ED record, the chief complaint is commonly used for coding diagnosis.

For Work-RISQS queries, diagnosis is coded into one of 24 categories. Coding of specific injury types may not always be uniform because of multiple diagnoses listed in the ED record and ambiguities in terminology. For example, a worker may strain or sprain their lower back while lifting an object. In one ED chart this may be noted as a strained back and coded as strain or sprain whereas in another case the chart may simply state "patient presented with back pain" resulting in a diagnosis code of "other, n.e.c." To the extent possible these types of issues have been minimized in the diagnosis data. Definitions of individual diagnoses commonly follow standard medical practice. Anoxia, aspirated foreign object, ingested foreign object, and poisoning have specific definitions to help distinguish particular injuries.

  Anoxia is used when the patient cannot obtain sufficient oxygen, owing to hampered breathing or lack of oxygen itself. For example, this category is used when the diagnosis is strangulation, suffocation, asphyxia, or the patient has inhaled combustion products such as carbon monoxide (CO), smoke, soot, etc.

Aspirated foreign object is used when an insoluble object causes choking or is caught in the nose, lungs, or other parts of the airways and the object does not lead to poisoning or anoxia.

Ingested foreign object is used when a patient swallowed an insoluble object that is not likely to cause poisoning.

Poisoning is used when a patient swallowed liquid or soluble chemicals, drugs, or medications including liquids such as bleach, fuel, or alcohol, and non-liquids such as powdered detergents or cleaning products. Poisoning is also used when a patient inhaled vapors, fumes, or gases (e.g., chemicals, cleaners, or fuels), except when the vapors are carbon monoxide or other combustion products such as smoke.

For Work-RISQS queries the 31 diagnosis categories used by NEISS-Work hospital abstracters have been condensed to 24 categories. Categories with few cases such as diagnoses of "Burn: electrical" and "Burn: not specified" have been combined into a larger reportable group ("Burn: other"). Diagnoses of "Ingested foreign object," "Aspirated foreign object," "Dental injury," "Hemorrhage," "Nerve damage," "Other," and "Submersion" have been combined as "Other, n.e.c." (not elsewhere classified). The diagnosis categories available for querying in Work-RISQS are:

All (default) Burn: other Contusions, abrasions Foreign body Poisoning
Amputation Burn: radiation Crushing Fracture Puncture
Anoxia Burn: scald Dermatitis, conjunctivitis Hematoma Strain or sprain
Avulsion Burn: thermal Dislocation Internal organ Other, n.e.c.
Burn: chemical Concussions Electric shock Laceration Not stated

Back To Top Part of body affected

Definition: The region or part of the body most seriously hurt.

The part of the body primarily or most severely affected by the injury or illness is coded. However, the injured body part may overlap two coding categories such as a laceration to a finger and palm where one coder may list the body part affected as finger and another as hand. Similarly an injury to the eye may be coded as eyeball or face depending upon the information and wording provided in the ED chart. Caution should be used in interpreting Work-RISQS estimates by body part when comparing to adjoining body parts or a specific part within a larger body region. Selected injury types have coding rules to minimize this issue.

  Back injuries are coded as upper trunk when the injury is above the waist or navel and lower trunk when below. A simple diagnosis of "back injury" is coded as upper trunk.

Burn injuries involving less than 25% of the body are coded as the most severely burned body part. More extensive burn injuries are coded as 25 to 50% of the body or all parts of the body (i.e., more than 50% of the body).

Eye injuries are coded as eyeball when the injury occurred directly to the eye itself, whereas injuries to the eyelids, eye brows, or the area immediately around the eyes are coded as face injuries in the original hospital data collection. However, NIOSH recodes eye and face injuries to conform to the BLS Occupational Injury and Illness Classification System definition of eye as the part of body affected. This definition classifies the sense organs of sight located in the frontal portion of the head and is used for either one or both eyes or when loss or impairment of sight is involved. In this definition the eye includes: conjunctiva, cornea, eyeball, inside and outside of the eyelids, iris, lacrimal glands, lens, optic nerve, orbit, retina, and upper and lower eyelashes. Injuries to the eye brow area originally misclassified as eye injuries have been recoded to face injuries.

Face injuries to primarily the eye area, as defined above, have been recoded to eye injuries. Injuries to the facial area that were unspecified or more generally involved a broader extent of the face are classified as face injuries although damage to one or both eyes or mouth may have occurred.

Head injuries with general diagnoses of "head trauma," "closed head injury," or "blunt head injury" and that do not have a specific diagnosis such as laceration or concussion are coded as internal organ.

Anoxia, electric shock, poisoning, and submersion are coded as all parts of the body.

Aspirated or ingested foreign object injuries are coded as internal organ.

The 26 individual part of body categories used by NEISS-Work hospital abstracters are all available for use in Work-RISQS queries. The part of body categories are:

All (default) Eye Internal Pubic Region 25-50% of body
Ankle Face Knee Shoulder All parts of body (>50%)
Arm, lower Finger Leg, lower Toe Not stated
Arm, upper Foot Leg, upper Trunk, lower
Ear Hand Mouth Trunk, upper
Elbow Head Neck Wrist

Back To Top ED disposition (treated and released vs hospitalized)

Definition: The status of a patient after treatment in the ED categorized as treated and released, treated and transferred/hospitalized, or unknown.

About half of treated and transferred/hospitalized patients are hospitalized in the same facility as the ED. The other half are transferred to a different facility, generally a specialty services hospital (e.g., a burn or pediatric hospital) or other higher level care facility. Many of the transferred patients are hospitalized in the new facility, but the final disposition is not always known.

Back To Top Event or exposure

Definition: The manner in which the injury or illness was produced or inflicted as coded in the BLS Occupational Injury and Illness Classification System (OIICS). The OIICS coding manual is available online from the BLS.

The event or exposure is classified in a hierarchical structure with general divisions:
  • contact with objects
  • falls
  • bodily reaction and exertion
  • exposure to harmful substances or environments
  • transportation accidents
  • fires and explosions
  • assaults and violent acts
  • other events or exposures
  • Nonclassifiable
Each case is coded to the most significant level of detail permitted by using the information abstracted from the ED record. Work-RISQS queries may be made to the four-digit level (most detailed) for specific events or reported by all subgroups by using the advance sort options. However, the more detailed levels may not produce tables with reportable results because of the rarity of the event or lack of detail in the ED record. For example, a worker who falls from a loading dock to the ground below may be coded as 1123 Fall from loading dock if the ED record and the abstractor provide that level of detail in the final NEISS-Work data. However, the same injury might also be described in the ED chart as "fell at work." In this instance, the event would be coded as 10 Fall, unspecified. This same circumstance gives rise to injury estimates for specific events that may significantly under estimate the true number because event details are never reported in the ED record. Thus, estimates for individual events should be considered as minimum estimates.

Back To Top Source of injury/illness

Definition: The object, substance, bodily motion, or exposure which directly produced or inflicted the injury or illness as coded in the BLS Occupational Injury and Illness Classification System.

The source is classified in a hierarchical structure with general divisions:
  • Chemicals and chemical products
  • Containers
  • Furniture and fixtures
  • Machinery
  • Parts and materials
  • Persons, plants, animals, and minerals
  • Structures and surfaces
  • Tools, instruments, and equipment
  • Vehicles
  • Other sources
  • Nonclassifiable
The injury source is coded in a similar fashion and level of detail as the injury event. However, there are far more codes available for source than event because of the diversity of objects etc. that could produce an injury. For example, if a worker were struck in the eye by a nail or brad, the source code would be 4212. Other fasteners such as bolts, screws, and staples each have separate 4-digit source codes. Estimates of specific sources should also be considered minimum estimates as described for injury event estimates.

Back To Top Secondary source of injury/illness

Definition: The object, substance, or person that generated the source of the injury or illness or that contributed to the event or exposure as coded in the BLS Occupational Injury and Illness Classification System.

The secondary source is classified in a hierarchical structure with the same codes as the source that inflicted the injury. An example of a secondary source would be a hand tool that generated a flying object where the object struck a worker. That is, if the worker noted above who was injured by a flying nail were hammering at the time, the hammer would be the secondary source that generated or contributed to the injury. Tools are common secondary sources, however, a secondary source is not coded for every case because of a lack of injury event details or because there simply was not a secondary source. About 80% of cases have no secondary source coded.

Back To Top Data reports

National Injury/Illness Estimates: A Work-RISQS injury estimate query results in a table of national injury and illness estimates where each table lists the query parameters selected for this particular estimate and results. The table includes a "National Estimate" in thousands, the percentage of the total estimated injuries/illnesses for the year, and the confidence bounds expressed as a value to be added to and subtracted from the national estimate to give the 95% confidence interval.

National Injury/Illness Rates: A Work-RISQS injury rate query results in a table of national injury and illness rate estimates where each table lists the query parameters selected and results. The table includes a "National Estimate" in thousands (i.e., the rate numerator and the same value that would be obtained from the injury estimate report option), the worker population in full time equivalent workers (i.e., the rate denominator), the injury/illness rate in incidents per 100 FTE during the time period, and the confidence bounds expressed as a value to be added to and subtracted from the national rate to give the 95% confidence interval.

Data notes: Accompanying each query results table are data notes that pertain to that specific query as well as several general notes.

Minimum reporting requirements: Work-RISQS uses three criteria to determine if a national estimate is reportable. First, estimates must be based on a minimum number of cases among the small sample of U.S. hospitals within NEISS-Work. Second, the national estimate must exceed a minimum number of injuries/illnesses. Third, the error associated with an estimate must be small enough to indicate that the estimate would be reasonably reproducible (i.e., the coefficient of variation is less than or equal to 33%). To be reportable a national estimate must meet all three criteria. Work-RISQS automatically checks that results meet the reporting requirements.

Disclaimer: Although NIOSH extends considerable effort to insure reasonable data quality for Work-RISQS estimates, there are no warranties expressed or implied with these data. The underlying data for queries are subject to change without notice as errors, inconsistencies, or other data issues arise. The objective of Work-RISQS is to provide public access to occupational injury and illness data for use in workplace safety and injury prevention activities where understanding the general magnitude of injuries, worker characteristics, and injury events are important. Use of these data for other purposes should be done with caution.

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