1 

Full Title: Injury classification agreement in linked Bureau of Labor Statistics and Workers’ 

Compensation data 

Running Title: Injury classification agreement in linked BLS and Workers’ Compensation data

ABSTRACT

BACKGROUND: Estimates of select occupational injuries and illnesses often differ across data sources. 

We explored agreement in injury classifications and the impact of differences on case estimates among 

records reported to multiple data sources. 

METHODS: We linked cases reported in the Bureau of Labor Statistics (BLS) annual Survey of 

Occupational Injuries and Illnesses (SOII) to Washington State workers’ compensation (WC) claims and 

evaluated agreement in injury characteristics coded in each data source according to the same 

occupational injury and illness classification system. 

RESULTS: Agreement between data sources was greatest for body part and lowest for event or 

exposure. Agreement on nature of injury varied by condition. WC-assigned injury codes estimated 94% 

more amputations than SOII-assigned codes while SOII-assigned codes estimated 34% more workrelated MSD cases. 

CONCLUSIONS: Accounting for classification differences may improve case ascertainment within 

individual data sources help align injury and illness estimates derived from different data sources. 

Corresponding author and contact information: 

Sara Wuellner, MPH 

Washington State Department of Labor and Industries 

Safety and Health Assessment and Research for Prevention (SHARP) Program 

PO Box 44330 

Olympia, WA 98504 

ph: 360-902-6727 

fx: 360-902-5672 

sara.wuellner@lni.wa.gov

Co-author: 

David K. Bonauto, MD, MPH 

Washington State Department of Labor and Industries 

Safety and Health Assessment and Research for Prevention (SHARP) Program 

Olympia, WA 

Conflict of Interest Statement: 

Neither author has a conflict of interest. 

Word count: 

5,060 
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INTRODUCTION 

Occupational health surveillance data are used to monitor workplace exposures and health effects, 

develop workplace interventions, and guide policy. Accurate data are essential to inform the 

appropriate allocation of limited research and prevention resources. The United States Bureau of Labor 

Statistics’ (BLS) Survey of Occupational Injuries and Illnesses (SOII), an annual survey of sampled 

business establishments, is one of the primary sources of work-related injury and illness data in the US, 

providing both national, and for most states, state level estimates of nonfatal occupational injuries and 

illnesses based on employer reports of OSHA recordable cases (US Department of Labor, 2012a). Over 

the years, SOII has been the focus of many researchers, policy analysts, and others in the occupational 

health community who question the completeness of the survey data. Several studies report a failure 

by SOII to capture all eligible injuries (Boden and Ozonoff, 2008; Leigh et al., 2004; Rosenman et al., 

2006) and other studies comparing SOII estimates of select conditions to cases identified through other 

data sources have concluded that SOII underestimates such conditions (Friedman et al., 2013; Kica and 

Rosenman, 2012; Lipscomb et al., 2008a; Morse et al., 2001). 

Potential reasons for the observed SOII undercount are many: incomplete employer reports of injuries 

and illnesses, whether intentional or inadvertent; inadequate understanding of the reporting 

requirements; and constraints of the survey’s methodology which limits the reporting of certain cases, 

including illnesses with long latencies, injuries that worsen over time, and those that are difficult to 

attribute to work (Azaroff et al., 2002; Dong et al., 2011; Nestoriak and Pierce, 2009; Pransky et al., 

1999; Ruser, 2008; Seligman et al., 1988). 

Another possible explanation for apparent low SOII case capture, yet to be explored, is the 

characterization of reported cases and whether it is consistent across data sources or differs by source. 

Identical injury events can appear distinct if the characterization of the injury differs by data source. For 

example, based on variant incident descriptions, a case may be coded as a crushing injury in the SOII but 

as an amputation in another data source. Depending on the data source used for case surveillance, this 

incident would be counted toward the total number of one condition instead of the other. Thus, 

differences in case classification may lead to divergent estimates of specific conditions. 

In this study, we assessed injury coding agreement among cases reported to multiple data sources and 

examined the impact of coding differences on estimates of select occupational injuries and illnesses. 
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METHODS 

Data Sources and Codes 

We linked three years of BLS SOII case data to Washington WC claims data to assess injury classification 

agreement among cases reported to both systems. 

During the study period, both data sources coded injury and illness characteristics according to the 

Occupational Injury and Illness Classification manual (OIICS) from 1992, with minor revisions adopted in 

2007. OIICS, developed by BLS, provides a classification system for coding four aspects of a work-related 

injury or illness: the principal physical characteristic or nature of the injury or illness; part of body 

affected; the source, namely objects, substances or other factors responsible for the injury or illness; 

and the event or exposure to describe the manner in which the injury or illness occurred (US 

Department of Labor, 1992, 2007). 

OIICS employs a hierarchical structure with up to four digits used to describe each aspect of the case. 

The first digit designates the division that represents general categories of case characteristics. The 

second digit designates the major group, and, in certain prescribed instances, a third and sometimes 

fourth digit are used to designate the group and subgroup, respectively. For example, for the 

characteristic nature of injury, the division Traumatic injuries and disorders (0*) contains ten major 

groups including Open wounds (03*) (an asterisk indicates the inclusion of all codes that begin with the 

character(s) listed). Nine of the ten groups within Open wounds, a partial list of which includes Animal 

or insect bites (032), Cuts, lacerations (034), and Gunshot wounds (036), allows for no more detail 

beyond the three digit group level. Among the groups in Open wounds, only Amputations (031*) 

includes subgroups: Amputations, fingertip (0311) and Amputations, except fingertip (0319). 

BLS SOII Data 

The BLS administers the SOII annually in partnership with participating states to estimate the incidence 

of nonfatal OSHA-recordable occupational injuries and illnesses. BLS collects work-related injury and 

illness data from sampled private sector employers as well as state and local governments. Sampled 

establishments are asked to submit the number of OSHA recordable cases that occurred within the 

survey year. For injuries and illnesses resulting in at least one day of missed work following the date of 

injury, employers send detailed worker and incident characteristics including worker name, date of birth 

or age, sex, date of injury, and a description of the injury or illness as well as the activity immediately 
4 

preceding the incident. Survey respondents are instructed to report detailed case information from any 

of the following sources: the OSHA Form 301; a workers’ compensation report; an accident report; or an 

insurance form. Following a protocol established by BLS, participating states code the injury descriptions 

according to OIICS. 

Washington State SOII data for survey years 2006-2008 were obtained through a cooperative agreement 

between the BLS and the Washington State Department of Labor and Industries (L&I). 

Washington WC Data 

L&I regulates workers’ compensation insurance for all non-federal employers operating in Washington 

State (Washington Revised Code, 1972). In addition, L&I administers the Washington state fund (SF) 

workers’ compensation insurance program which is the sole workers’ compensation insurance provider 

for all employers in the state except those covered by an alternate workers’ compensation system (e.g. 

Longshore and Harbor Workers’ Compensation Act, Federal Employees’ Compensation Act), specific 

employers or occupations exempt from mandatory coverage (e.g. self-employed), or those who are able 

to self-insure. Approximately 70% of workers under L&I jurisdiction are covered by SF employers and 

30% work for a self-insured employer. 

A workers’ compensation claim is initiated when a worker and the health care provider complete and 

submit a report of industrial injury or occupational disease (RIIOD). All filed SF claims, regardless of 

claim acceptance or award, are coded by trained L&I staff who review the narrative description of the 

incident and the resulting injury or illness as provided on the RIIOD to assign codes according to OIICS. 

In contrast, only a portion of self-insured claims awarded indemnity payments are coded for injury 

characteristics (in Washington, the waiting period for indemnity is three calendar days following the day 

of injury). 

All filed workers’ compensation claims with an injury date in 2006-2008 were extracted from the L&I 

workers’ compensation database on July 13, 2010. The claims data extracted included claimant name, 

sex, date of birth, date of injury or illness, employer name and address, and OIICS Nature, Event or 

Exposure, and Part of Body codes. 

Record Linkage 

Record linkage procedures were patterned after those developed by researchers for another study 

linking similar BLS case data to WC claims data (Boden and Ozonoff, 2008). In preparation for linking, 
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first names and addresses were standardized using the US Census Bureau’s data standardization 

software GDRIVER (US Bureau of the Census, 1999). Linking was attempted between SOII cases (OSHA 

recordable injuries and illnesses resulting in one or more days of missed work) and all filed WC claims 

among SF and self-insured employers, and was conducted in two stages. First, we linked cases to claims 

through identical matches on eight of the nine common variables: worker last name, first initial, sex, 

date of birth or age at injury, date of injury, employer name, employer address, zip code or city, and 

federal employer identification number. We then linked the remaining unmatched cases using the 

probabilistic software program LinkPlus (US Department of Health and Human Services, 2007), which 

assigns a score to each potential matched pair based on the degree of similarity in the common 

variables. Two researchers reviewed pairs with lower scores to determine whether to accept the 

potential match. Disagreements between the two reviewers were settled by a third reviewer. We 

allowed some difference in injury dates between data sources, although date differences were not 

allowed to exceed two months. Because the injury date in WC is adjudicated to reflect the last injurious 

exposure, the date reported by the employer may not be identical, especially for non-traumatic 

conditions with no clear precipitating event. The injury date documented by the employer may be the 

date the worker received medical treatment or the date of missed or restricted work. Injury dates more 

than two months apart were assumed to reflect separate injury events rather than differences in the 

characterization of one singular event. 

Data Analysis 

The analysis of injury and illness classification agreement was limited to linked SF claims because injury 

classification codes are not systematically assigned to self-insured claims. More commonly assigned 

OIICS codes were assessed individually while less common codes were aggregated within major groups 

or divisions. 

The BLS assigns each reported case a sample weight that is used to estimate the number and rate of 

nonfatal occupational injuries and illnesses among the population. Using the SOII sample weights 

assigned to each case, two population estimates for each selected condition were calculated for 

comparison: one based on injury and illness characteristics as coded in SOII and a second based on 

characteristics as coded in WC. We selected for estimation two conditions that state-based surveillance 

efforts monitor using the SOII data: amputations and musculoskeletal disorders (Council of State and 

Territorial Epidemiologists, Updated 2012). The CSTE surveillance definitions of amputations and 

musculoskeletal disorders (MSD) are based on 1992 OIICS codes. Amputations are defined as cases with 
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an Amputation Nature code (031*). Musculoskeletal disorders are defined as cases with an MSD-related 

Nature code and an MSD-related Event code (OIICS Nature codes: 021 (Sprains, strains, tears); 0972 

(Back pain, hurt back); 0973 (Soreness, pain, hurt, except back); 1241 (Carpal tunnel syndrome); 153* 

(Hernia); or 17* (Musculoskeletal system and connective tissue diseases and disorders) and OIICS Event 

codes: 211 (Bending, climbing, crawling, reaching, twisting); 22* (Overexertion); or 23* (Repetitive 

motion)). 

Kappa statistics, a measure of agreement adjusted for chance (Landis and Koch, 1977), were used to 

measure agreement in OIICS codes among matched SOII-WC records for three injury characteristics: 

Nature, Part of Body, and Event. Agreement was assessed for divisions, major groups, groups, and 

subgroups. When a major group or group was the greatest level of detail available in OIICS, the case 

was included in the analysis of more detailed classifications. McNemar’s test was used to assess 

differences in proportions of select injury classifications among the matched cases (McNemar, 1947). 

Neither data source was regarded as the referent. All analyses were performed using SAS version 9.3. 

The Washington State Institutional Review Board approved the study. 

RESULTS

Record linkage procedures matched 90% of the 29,862 SOII cases to WC claims, a total of 26,925 linked 

records. Links among SF WC claims totaled 15,447 claims (57%) and the remaining cases linked to WC 

claims among self-insured employers. SOII and WC data documented identical injury dates in 14,049 SF 

claims (91% of linked SF claims); injury dates were within 7 days in 14,943 linked SF claims (97%). 

Among the 15,447 SOII cases linked to SF WC claims, Sprains, strains, tears were the most common 

injury or illness assigned in either SOII or WC (48% and 40%, respectively) and backs were the most 

frequently affected body part (23% of linked SOII cases, 24% of linked WC claims). WC classified more 

cases than SOII as non-traumatic (1519 records compared with 1099 records, p<.01) although SOII coded 

27 more cases as Carpal tunnel syndrome, the most frequently assigned non-traumatic Nature 

classification in either data source (236 records based on SOII-assigned codes, 209 records based on WCassigned codes). Overexertion, specifically in lifting, was the most frequently-assigned exposure, with a 

similar number of cases classified as Overexertion in SOII (4299 records) as in WC (4300 records). 
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One in five linked records (3,205 cases) was classified identically in both data sources for all three injury 

characteristics: Nature, Part of Body, and Event. For 1,426 linked records (9%), none of the injury 

characteristics matched across data sources. 

Classification agreement varied by injury characteristic and level of coding detail, with the portion of 

records in agreement decreasing as coding detail increased (Table I). For each injury characteristic 

(Nature, Body Part, and Event), at least 85% of cases linked to SF claims were coded identically in both 

data sources at the most general (1 digit) division level. For Nature and Body Part, one in three cases 

were assigned to groups (3-digit codes) that differed by data source. For Event, over half were assigned 

to groups (3-digit codes) that differed by data source. 

Nature of Injury Classification 

Over 90% of linked records were classified in SOII as one of thirteen 3-digit group codes: ten within 

traumatic injuries and three within systemic conditions or disorders. Among those thirteen group codes, 

agreement with WC-assigned Nature was lowest for Nonspecified injuries and disorders (k=0.19), and 

greatest for Hernia (k=0.89) and Heat burns, scalds (k=0.89). Agreement for the most frequentlyassigned code, Sprains, strains, tears (k=0.68), was exceeded only by agreement among cases classified 

as Hernia or Heat burns, scalds, although one in four cases classified in SOII as Sprains, strains, tears was

classified differently in WC. Twenty percent of SOII-designated Sprains, strains, tears were classified in 

WC as some other traumatic injury or disorder, including: 7% as Multiple Traumatic Injuries and 

Disorders; 4% as Dislocations; and 4% as Nonspecified injuries and disorders. Four percent of SOIIdesignated Sprains, strains, tears were classified in WC as Systemic diseases and disorders. For four of 

the thirteen most frequently SOII-assigned groups, cases not coded identically in WC were most often 

assigned another group within the SOII-assigned major group. When not coded identically in WC, SOIIassigned Cuts, lacerations were classified in WC as some other Open wound more than any other group 

code; SOII-assigned Abrasions, scratches and Foreign bodies were most often classified as some other 

Surface wounds and bruises in WC; and SOII-assigned Heat burns, scalds appeared in WC as some other 

burn. More than 10% of cases within each of the following six SOII-assigned groups had codes assigned 

in WC that differed at the 1-digit division level: Rheumatism; Peripheral nerve damage; Nonspecified 

injuries and disorders; Hernia; Foreign bodies; and Punctures. When not classified identically in WC, 

cases classified in SOII as Bruises, contusions or Fractures were more often assigned the code for 

Multiple Traumatic Injuries and Disorders than any other classification. 
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Table II presents the distribution of cases by the 2-digit major group codes assigned in each data source 

characterizing Nature. Even at this more general level of detail, coding disagreements between the two 

data sources persist. Of the 1344 cases coded as Traumatic injuries to bones, nerves, spinal cord (9% of 

linked records), 72% were classified the same in WC, 15% had a WC-assigned code for Multiple 

traumatic injuries and disorders, and the remaining 13% of SOII-designated cases of traumatic injuries to 

bones, nerves, spinal cord were classified in WC as one of twelve other major groups, including nontraumatic conditions or disorders. For most traumatic major groups, injuries not classified the same in 

both data sources were often classified as Multiple traumatic injuries and disorders in WC. 

Agreement was better among traumatic injuries than non-traumatic conditions or disorders. Of the 

14,348 linked records classified in SOII as Traumatic injuries or disorders, 66% had an identical Nature 

code assigned in WC, and 29% had a non-identical WC-assigned code within the traumatic injury 

division, including 8% with a WC-assigned code for multiple traumatic injuries. Among SOII’s 1035 

Systemic diseases and disorders, 55% were coded identically in WC, 21% were assigned a different code 

within the Systemic diseases and disorders division, and another 21% had a WC-assigned code within the 

Traumatic injuries or disorders. An additional 3% of SOII-designated Systemic diseases and disorders

were classified in WC within some division other than Systemic diseases and disorders or Traumatic 

injuries or disorders. 

Over 75% of linked cases were categorized in SOII using one of twelve body part codes. Among those 

twelve, high agreement with WC coding was found for five body parts (33% of SOII-designated cases): 

Eye, Knee, Finger, Ankle, and Shoulder (k>0.80), and lower agreement was found for Wrist(s), Foot, 

Lumbar region, Hand, and External neck injuries (kappa ranged from 0.76 to 0.60). Among body parts 

with less agreement, often codes assigned in WC described proximate body parts. Of the SOIIdesignated wrist injuries, 71% not coded identically in WC were coded as Finger, Hand, Arm, or Multiple 

upper extremities. Among SOII-classified injuries involving an unspecified part of the foot, 81% of cases 

those without a matching code in WC were classified in WC as Toe(s), Ankle(s), or some other part of the 

foot. Three out of four cases coded in SOII as involving the lumbar region and a different body part 

assigned in WC were classified as some other region of the back in WC, often Multiple back regions or 

Back, including spine, spinal cord, unspecified. Among SOII hand injuries, 85% of those not classified as 

such in WC were classified as Finger(s), Wrist(s), Arm(s), or Multiple upper extremities. 
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Body part classifications not in agreement at the division level were often coded as injuries to Multiple 

Body Parts in one of the two data sources (Table III). In both data sources, 11% of records were 

classified as injuries to Multiple Body Parts (p=0.86), however, within-case agreement was modest 

(k=0.49). 

Over ninety percent of cases were classified in SOII within three Event or Exposure divisions: Bodily 

reaction and exertion (44%); Contact with objects and equipment (27%); and Falls (19%). Within Bodily 

reaction and exertion, Overexertion (28%, k=0.77) was most commonly assigned, followed by Bodily 

reaction (12%, k=0.55), and Repetitive motion (4%, k=0.59) (Table IV). When not assigned an identical 

code in WC, Bodily reaction cases were generally classified as Overexertion and SOII-designated 

Overexertion cases were often coded in WC as Bodily reaction. 

Within the division Contact with objects and equipment, agreement was greatest for Rubbed or abraded 

by fiction or pressure (k=0.74) and lowest for Struck against object or equipment (0.43). Like Bodily 

reaction and exertion, differences in coding were usually limited to the major group level, and 

agreement was high for the division (k=0.81). Among Falls, agreement was greater for Falls to lower 

level (k=0.71) than Falls on same level (k=0.65). More than one in three cases classified in SOII as Falls 

on same level were classified as some other event or exposure in WC including: Falls to lower level; 

Bodily reaction; and Struck against object or equipment. 

Impact of discordant injury characterization on case estimates of select conditions 

BLS weights each case reported in SOII to estimate the incidence of cases among the population. To 

examine the impact of coding differences on occupational injury and illness case estimates, we applied 

the SOII sample weights to reported cases of amputations and musculoskeletal disorders, identified 

through SOII-assigned codes or WC-assigned codes. 

Among the 15,447 matched cases, 98 amputations were identified from the SOII-assigned codes and 119 

from the WC-assigned codes (k=0.65). Among the 119 cases classified in WC as Amputations, 60% were 

classified in SOII as Amputations, 18% as Cuts, lacerations, 8% as Avulsions, 6% as Fractures, 5% as 

Crushing injuries, and the remaining 3% as some other traumatic injury. Among the 98 SOII-identified 

Amputations, 72% appeared in WC as Amputations, 11% as Multiple traumatic injuries and disorders, 

11% as some other Open wound, and 5% as some other traumatic injury. Applying the SOII sample 

weights, there were an estimated 449 amputations based on the SOII nature of injury classifications and 

an estimated 871 amputations based on the WC classifications, an increase of 94% over the SOII 
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estimate. Based on classification codes assigned in either SOII or WC, 146 cases were identified as 

amputations, representing an estimated 985 amputations. 

SOII-designated coding identified 5922 MSD cases, 1299 more cases than the 4623 MSD cases based on 

WC classifications (k=0.71). Among the 2071 cases identified as an MSD in one data source but not the 

other, 57% were assigned an MSD related nature of injury code but lacked an MSD related event or 

exposure code, 29% had an MSD related event or exposure code but lacked an MSD related nature of 

injury code, and 14% lacked both the event or exposure codes and the nature of injury codes used to 

identify MSD. After applying the SOII sample weights, the estimated number of MSD cases was 34% 

higher based on the SOII-assigned classification codes compared with the WC-assigned codes (32,172 

estimated cases compared with 24,066 estimated cases). Based on classification codes assigned in 

either SOII or WC, 6278 cases were identified as MSD, representing an estimated 34,216 MSD cases. 

DISCUSSION 

Linking occupational injury and illness records from multiple data sources allowed us to compare injury 

classification codes assigned by two different systems to the same work-related incident. This is the first 

study we know of to measure agreement in injury coding between SOII cases and WC claims and to 

assess the impact of coding differences on case estimates. 

There are several possible explanations for the differences in the injury classification codes assigned in

SOII compared with WC. First, the forms used to collect the descriptions of the events differ. Compare 

the questions posed by each system to illicit the injury narratives that are then coded. 

SOII form: 

 What happened? Tell us how the injury or illness occurred. Examples: “When ladder slipped on 

wet floor, worker fell 20 feet”; “worker was sprayed with chlorine when gasket broke during 

replacement”: “Worker developed soreness in wrist over time” and 

 What was the injury or illness? Tell us the part of the body that was affected and how it was 

affected; be more specific than “hurt”, “pain”, or “sore”. Examples: “strained back”; chemical 

burn, hand”; “carpal tunnel syndrome” 

WC accident report: 
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 Describe in detail how your injury or exposure occurred. Include tools, machinery, chemicals, or 

fumes that may have been involved. 

 Part of body injured or exposed

The examples provided in the SOII questions may lead the survey respondent’s description of the 

incident and injury or illness to conform to the examples provided. Indeed, among matched cases, a 

greater portion was coded in SOII as “strained backed” and “carpal tunnel syndrome” while WC codes 

reflected a greater variety of injury types. 

Another possible explanation for differences in injury assignments may relate to the individuals involved 

in the documentation of the incidents. An injury or illness record keeper from the sampled 

establishment provides the narrative description of the incident for the SOII. There may be a desire to 

downplay the severity of the injury (more injuries characterized in SOII as Surface Wounds or Bruises, 

injuries classified in WC as Amputations that were classified in SOII as Cuts, Lacerations, Avulsions, or 

some other injury) or, in characterizing the event, shifting blame on the worker to mitigate an 

employer’s sense of culpability. 

WC claims are coded from injured workers’ narratives of the injury and event on the initial accident 

report. The report is completed by the worker and the attending physician, each of whom are 

responsible for separate sections of the form. The worker’s interaction with the health care provider 

likely influences the worker’s description of the injury. The worker’s account may be more medically 

technical and detailed after discussing the condition with the health care provider. This may explain the 

higher portions of systemic diseases and multiple injuries among WC codes compared with SOII codes. 

Additionally, when coders are unable to classify the injury based on the accident report, they review the 

medical records related to the WC claim to gather the necessary information. Employer injury and 

illness records are unlikely to include the detail contained in medical documents, and can be expected to 

describe the injuries using commonplace terms rather than medical terminology. 

The timing of the injury reports may offer yet another explanation for the differences in codes. 

Employers are required to record injuries on their OSHA logs (which provide the source data for SOII) 

within seven days of recordability. In Washington, workers, with their health care providers, are entitled 

to file a WC claim within one year of injury and within two years of written notification of an 

occupational disease and the ability to file a claim. Descriptions of injuries may be modified over time as 

the injury is evaluated and diagnoses are refined so that the employer’s description of the injury or 
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illness at the time the case is recorded on the OSHA log may differ from the description provided by the 

worker at the time of claim filing. 

Compared to SOII estimates, studies utilizing other sources of occupational injury and illness data 

including medical, hospital, WC data, or data combined from multiple sources consistently identify more 

cases of select conditions including amputations(Anderson et al., 2010; Friedman et al., 2013), burns 

(Kica and Rosenman, 2012), and musculoskeletal disorders (Lipscomb et al., 2008b; Silverstein et al., 

1998). While other factors may contribute to differences in case capture (including different case 

definitions, inclusion of non-surveyed populations, and underreporting to SOII), some of the 

discrepancy between the SOII case estimate and the case ascertainment achieved using other data 

sources may be explained by discordant injury characterization. The degree of discordant injury 

classification can be determined only by matching complete data sources, prior to applying exclusion or 

selection criteria. The implication of not doing so is the possible erroneous conclusion of incomplete 

case capture within individual data systems. 

In this study, estimates of amputations and MSD varied based on the source of the injury and illness 

classification. WC classifications resulted in an estimated number of amputations that was nearly twice 

the number of cases estimated from SOII classifications, while approximately one-third more MSD cases 

were estimated from SOII injury classifications compared to WC injury classifications. The greater 

difference in the amputation estimate may be due to the restrictiveness of the surveillance definition 

that is limited to a single group code. The MSD definition employed by CSTE is broader and 

encompasses multiple possible codes. For example, a case classified as Sprains, strains, tears in one 

data source and as a Back pain in another source could be included in the estimate of MSD cases. Also, 

as a rare occurrence, each amputation reported constitutes a greater portion of the total number of 

amputation cases compared to the contribution of a single MSD case to the total number of MSD cases. 

Classification differences among rare events may have a substantial impact on case estimates compared 

to estimates of more common injuries and conditions. 

There are several limitations to this study. Narrative descriptions of the injuries were not reviewed to 

assess the accuracy of the assigned codes. Thus, we are unable to know whether the assigned codes 

appropriately characterized the incident. Additionally, we were unable to assess the training provided to 

either group of coders to determine whether it might account for differences between SOII-assigned 

codes and WC-assigned codes. Another limitation is that the WC data for the study was limited to SF 

claims data from Washington State. Data from WC systems with different coding procedures, claim 
13

filing processes, and injury documentation may result in alternate findings. Coding agreement will likely 

be greater in systems with higher source dependence between SOII data and WC records, and less in 

systems with independent data sources. 

Our record linking procedures may not have identified all true matches between SOII cases and WC 

claims, failing to link some true matches and, conversely, linking some false matches. False linkages 

would likely have dissimilar injury characteristics, artificially lowering coding agreement. True matches 

left unlinked because of dissimilar record linkage variables may or may not have dissimilar injury 

characteristics. It is unknown whether omitting these true matches improves coding agreement. 

Further studies comparing the description of the injury provided in SOII to the description reported on 

the WC incident report, as well as any available incident or medical documentation would be able to 

assess whether classification differences are attributable to inter-rater coding choices, injury 

development that occurred between employer recording and WC claim filing, or the individual 

perspectives of those providing the narratives. 

BLS adopted a new version of the injury and illness classification system, OIICS 2.0 followed shortly by 

version 2.01, beginning with 2011 SOII data (US Department of Labor, 2012b). One of the objectives of 

the major revision was to increase uniformity by clarifying coding rules (Northwood et al., 2012). This 

newer version of the classification system may ease the selection of codes among conditions more 

difficult to characterize using the old version, potentially improving the accuracy of SOII estimates and 

reducing some of the observed differences in injury classification by data source. Additional coder 

training focused on the appropriate use of non-specific and multiple injury codes may further improve 

injury data. 

Given the differences in injury and illness classifications, surveillance efforts that compare estimates of 

select conditions across data sources without matching cases undoubtedly will conclude that case 

numbers or estimates differ by data source. Injuries reported to a system, such as SOII or WC, but 

classified in a way that excludes them from meeting a particular surveillance definition can make a 

valuable contribution to surveillance data. A multi-facetted approach that incorporates various aspects 

of the incident may improve case ascertainment; however it may do so at the expense of specificity. 
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ACKNOWLEDGEMENTS

The study was supported by Cooperative Agreement Number OS-20358-11-75-J-53 from the Bureau of 

Labor Statistics. 
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17

Table I. Agreement in injury classification codes* by level of coding detail among 15,447 SOII cases linked to Washington State Fund WC claims. 

Data presented are number of linked records with matching codes, percent of total linked records, and kappa statistic. 

Division

(1-digit code)

Major Group

(2-digit code)

Group

(3-digit code)

Subgroup 

(4 digit-code)

n % kappa n % kappa n % kappa n % kappa

Nature of injury or illness

 

14,525 94% 0.62

 

10,966 71% 0.62

 

10,268 67% 0.57

 

10,041 65% 0.55

Part of body

 

13,376 87% 0.82

 

11,844 77% 0.74

 

10,100 65% 0.63

 

10,091 65% 0.63

Event or exposure

 

13,055 85% 0.78

 

10,672 69% 0.64

 

6,875 45% 0.42

 

6,647 43% 0.40

*Both the SOII and WC cases were coded using the Occupational Injury and Illness Classification System, a hierarchical classification system with 

general categories containing codes of greater specificity. Most codes available in OIICS are 3- or 4-digits in length, although some are limited to 

1- or 2-digits. The most general category, the Division, is designated by the first digit of the code. To assess agreement in assignment of the 

Division, codes were aggregated to the first digit. Major Group included aggregation to the 2-digit level plus codes with no more detail beyond 

the 1-digit Division level. Group included aggregation to the 3-digit level plus terminal 1- and 2-digit codes. Subgroup consists of all codes as 

assigned with no aggregation. 
18

Table II. Linked records by WC and SOII nature of injury coding† (n=15,447). Data presented are n (%). 

WC-assigned codes

SOII-assigned codes

Traumatic 

injuries to 

bones, 

nerves, 

spinal cord 

(01*)

Traumatic 

injuries to 

muscles, 

tendons, 

ligaments, 

joints, etc. 

(02*)

Open 

wounds 

(03*)

Surface 

wounds 

and 

bruises 

(04*)

Burns 

(05*)

Multiple 

traumatic 

injuries 

and 

disorders 

(08*)

Other 

traumatic 

injuries 

and 

disorders 

(09*)

Systemic 

diseases 

and 

disorders 

(1*)

All others Total

Traumatic injuries to bones, nerves, 

spinal cord (01*)

972 (6) 378 (2) 55 (<1) 41 (<1) 0 (0) 84 (1) 57 (<1) 7 (<1) 3 (<1) 1597 (10)

Traumatic injuries to muscles, 

tendons, ligaments, joints, etc. (02*)

62 (<1) 5760 (37) 15 (<1) 94 (1) 1 (<1) 91 (1) 227 (1) 93 (1) 8 (<1) 6351 (41)

Open wounds (03*) 28 (<1) 28 (<1) 1145 (7) 46 (<1) 2 (<1) 39 (<1) 52 (<1) 9 (<1) 4 (<1) 1353 (9)

Surface wounds and bruises (04*) 39 (<1) 149 (1) 59 (<1) 1257 (8) 9 (<1) 89 (1) 62 (<1) 31 (<1) 11 (<1) 1706 (11)

Burns (05*) 0 (0) 2 (<1) 1 (<1) 6 (<1) 204 (1) 1 (<1) 3 (<1) 23 (<1) 0 (0) 240 (2)

Multiple traumatic injuries and 

disorders (08*)

199 (1) 520 (3) 123 (1) 241 (2) 2 (<1) 561 (4) 72 (<1) 18 (<1) 57 (<1) 1793 (12)

Other traumatic injuries and 

disorders (09*)

24 (<1) 362 (2) 18 (<1) 78 (1) 3 (<1) 29 (<1) 213 (1) 29 (<1) 11 (<1) 767 (5)
19

Systemic diseases and disorders (1*) 6 (<1) 303 (2) 33 (<1) 60 (<1) 17 (<1) 4 (<1) 73 (<1) 794 (5) 11 (<1) 1301 (8)

All others 14 (<1) 76 (<1) 10 (<1) 41 (<1) 4 (<1) 18 (<1) 36 (<1) 31 (<1) 109 (1) 339 (2)

Total 1344 (9) 7578 (49) 1459 (9) 1864 (12) 242 (2) 916 (6) 795 (5) 1035 (7) 214 (1) 15,447 (100)

† Both the SOII and WC cases were coded using the Occupational Injury and Illness Classification System. 

* Codes with greater detail aggregated at the level indicated. 
20

Table III. Linked records by WC and SOII body part coding† (n=15,447). Data presented are n (%).

WC-assigned codes

SOII-assigned codes

Head 

(0*)

Neck, 

including 

throat (1*)

Back, 

including 

spine, 

spinal cord 

(23*)

Trunk, 

excluding 

back (2* 

other than 

23) 

Finger(s), 

fingernail(s) 

(34)

Upper 

extremities,

excluding 

fingers (3* 

other than 

34) 

Lower 

Extremities 

(4*)

Multiple 

Body Parts 

(8) All others Total

Head (0*) 914 (6) 7 (<1) 4 (<1) 3 (<1) 7 (<1) 11 (<1) 7 (<1) 37 (<1) 1 (<1) 991 (6)

Neck, including throat (1*) 7 (<1) 163 (1) 5 (<1) 12 (<1) 0 (0) 5 (<1) 2 (<1) 50 (<1) 1 (<1) 245 (2)

Back, including spine, spinal cord 

(23*)

5 (<1) 43 (<1) 3228 (21) 114 (1) 4 (<1) 8 (<1) 22 (<1) 345 (2) 2 (<1) 3771 (24)

Trunk, excluding back (2* other 

than 23)

7 (<1) 8 (<1) 132 (1) 1640 (11) 3 (<1) 38 (<1) 20 (<1) 167 (1) 19 (<1) 2034 (13)

Finger(s), fingernail(s) (34) 6 (<1) 0 (0) 9 (<1) 3 (<1) 1229 (8) 108 (1) 19 (<1) 6 (<1) 4 (<1) 1384 (9)

Upper extremities, excluding 

fingers (3* other than 34) 

5 (<1) 6 (<1) 10 (<1) 53 (<1) 155 (1) 1766 (11) 35 (<1) 79 (1) 12 (<1) 2121 (14)

Lower Extremities (4*) 2 (<1) 1 (<1) 24 (<1) 28 (<1) 7 (<1) 20 (<1) 2945 (19) 64 (<1) 5 (<1) 3096 (20)

Multiple Body Parts (8) 109 (1) 67 (<1) 149 (1) 200 (1) 12 (<1) 90 (1) 121 (1) 904 (6) 15 (<1) 1667 (11)

All others 10 (<1) 1 (<1) 5 (<1) 15 (<1) 1 (<1) 8 (<1) 11 (<1) 8 (<1) 79 (1) 138 (1)
21

Total 1065 (7) 296 (2) 3566 (23) 2068 (13) 1418 (9) 2054 (13) 3182 (21) 1660 (11) 138 (1) 15,447 (100)

† Both the SOII and WC cases were coded using the Occupational Injury and Illness Classification System. 

* Codes with greater detail aggregated to the level indicated. 
22

Table IV. Linked records by WC and SOII event or exposure coding† (n=15,447). Data presented are n (%).

WC-assigned codes

SOII-assigned codes

Contact 

with 

objects and 

equipment 

(0*) Falls (1*)

Bodily 

reaction 

(21*)

Overexertion 

(22*)

Repetitive 

motion (23*)

Exposure to 

harmful 

substances or 

environments 

(3*)

Transportation 

accidents (4*) All others Total

Contact with objects and 

equipment (0*)

3646 (24) 204 (1) 155 (1) 106 (1) 15 (<1) 42 (<1) 94 (1) 26 (<1) 4288 (28)

Falls (1*) 145 (1) 2367 (15) 190 (1) 41 (<1) 0 (0) 1 (<1) 14 (<1) 11 (<1) 2769 (18)

Bodily reaction (21*) 76 (<1) 217 (1) 1087 (7) 265 (2) 83 (1) 0 (0) 2 (<1) 1 (<1) 1731 (11)

Overexertion (22*) 152 (1) 48 (<1) 290 (2) 3601 (23) 175 (1) 5 (<1) 3 (<1) 26 (<1) 4300 (28)

Repetitive motion (23*) 7 (<1) 5 (<1) 18 (<1) 59 (<1) 333 (2) 0 (0) 0 (0) 3 (<1) 425 (3)

Exposure to harmful substances or 

environments (3*)

34 (<1) 2 (<1) 2 (<1) 3 (<1) 5 (<1) 467 (3) 0 (0) 7 (<1) 520 (3)

Transportation accidents (4*) 37 (<1) 14 (<1) 5 (<1) 5 (<1) 0 (0) 1 (<1) 453 (3) 3 (<1) 518 (3)

All others 132 (1) 94 (1) 114 (1) 219 (1) 61 (<1) 51 (<1) 14 (<1) 211 (1) 896 (6)

Total 4229 (27) 2951 (19) 1861 (12) 4299 (28) 672 (4) 567 (4) 580 (4) 288 (2) 15,447 (100)

† Both the SOII and WC cases were coded using the Occupational Injury and Illness Classification System. 

* Codes with greater detail aggregated to the level indicated.