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Thursday, 24 March 2011 16:26

Risk Analysis of Nonfatal Workplace Injuries and Illnesses

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The United States Bureau of Labor Statistics routinely classifies nonfatal workplace injuries and illnesses by worker and case characteristics, using data from the US Survey of Occupational Injuries and Illnesses. While these counts identify groups of workers who experience large numbers of workplace injuries, they do not measure risk. Thus a particular group may sustain many workplace injuries simply because of the large number of workers in that group, and not because the jobs performed are especially hazardous.

In order to quantify actual risk, data on workplace injuries must be related to a measure of exposure to risk, such as number of hours worked, a labour supply measure which may be available from other surveys. The rate of nonfatal workplace injuries for a group of workers may be calculated by dividing the number of injuries recorded for that group by the number of hours worked during the same time period. The rate obtained this way represents the risk of injury per hour of work:

A convenient way of comparing the risk of injury among various groups of workers is to compute the relative risk:

The reference group may be a special group of workers, such as all managerial and professional specialty workers. Alternatively, it might consist of all workers. In any case, the relative risk (RR) corresponds to the rate ratio commonly used in epidemiological studies (Rothman 1986). It is algebraically equivalent to the percentage of all injuries which occur to the special group divided by the percentage of hours accounted for by the special group. When the RR is greater than 1.0, it indicates that members of the selected group are more likely to sustain injuries than members of the reference group; when the RR is less than 1.0, it indicates that, on the average, members of this group experience fewer injuries per hour.

The following tables show how indexes of relative risk for different groups of workers can identify those at greatest risk of workplace injury. The injury data are from the 1993 Survey of Occupational Injuries and Illnesses (BLS 1993b) and measure the number of injuries and illnesses with days away from work. The calculation relies upon estimates of annual hours worked taken from the microdata files of the US Bureau of the Census Current Population Surveys for 1993, which is obtained from household surveys (Bureau of the Census 1993).

Table 1 presents data by occupation on the share of workplace injuries, the share of hours worked and their ratio, which is the RR for injuries and illnesses with days away from work. The reference group is taken to be “All nonfarm private industry occupations” with workers of age 15 and older, which comprises 100%. As an example, the group “Operators, fabricators and labourers” experienced 41.64% of all injuries and illnesses, but contributed only 18.37% of the total hours worked by the reference population. Therefore, the RR for “Operators, fabricators and labourers” is 41.64/18.37 = 2.3. In other words, workers in this group of occupations have on average 2.3 times the injury/illness rate of all nonfarm private industry workers combined. Furthermore, they are about 11 times as likely to sustain a serious injury as employees in a managerial or professional specialty.

Table 1. Risk of occupational injuries and illnesses

Occupation

Percentage1

Index
of relative risk

 

Injury and illness cases

Hours worked

 

All nonfarm private industry occupations

100.00

100.00

1.0

Managerial and professional specialty

5.59

24.27

0.2

Executive, administrative and managerial

2.48

13.64

0.2

Professional specialty

3.12

10.62

0.3

Technical, sales and administrative support

15.58

32.19

0.5

Technicians and related support

2.72

3.84

0.7

Sales occupations

5.98

13.10

0.5

Administrative support, including clerical

6.87

15.24

0.5

Service occupations2  

18.73

11.22

1.7

Protective service3

0.76

0.76

1.0

Service occupations, except protective  service

17.97

10.46

1.7

Farming, forestry and fishing occupations4

1.90

0.92

2.1

Precision production, craft and repair

16.55

13.03

1.3

Mechanics and repairers

6.30

4.54

1.4

Construction trades

6.00

4.05

1.5

Extractive occupations

0.32

0.20

1.6

Precision production occupations

3.93

4.24

0.9

Operators, fabricators and labourers

41.64

18.37

2.3

Machine operators, assemblers and  inspectors

15.32

8.62

1.8

Transportation and material moving  occupations

9.90

5.16

1.9

Handlers, equipment cleaners, helpers  and laborers

16.42

4.59

3.6

1 Percentage of injuries and illnesses, hours worked and index of relative risk for occupational injuries and illnesses with days away from work, by occupation, US nonfarm private industry employees 15 years and over, 1993.
2 Excludes private household workers and protective service workers in the public sector
3 Excludes protective service workers in the public sector
4 Excludes workers in agricultural production industries
Sources: BLS Survey of Occupational Injuries and Illnesses, 1993; Current Population Survey, 1993.

 

The various occupational groups may be ranked according to degree of risk simply by comparing their RR indices. The highest RR in the table (3.6) is associated with “handlers, equipment cleaners, helpers and labourers”, while the group at lowest risk is managerial and professional specialty workers (RR = 0.2). More refined interpretations may be made. While the table suggests that workers with lower levels of skills are in jobs with higher risks of injury and illness, even among blue-collar occupations the injury and illness rate is higher for less-skilled operators, fabricators and labourers compared to precision production, craft and repair workers.

In the above discussion, the RRs have been based upon all injuries and illnesses with days away from work, since these data have long been readily available and understood. Using the extensive and newly developed coding structure of the Survey of Occupational Injuries and Illnesses, researchers may now examine specific injuries and illnesses in detail.

As an example, table 2 shows the RR for the same set of occupation groupings, but restricted to the single outcome “Repetitive Motion Conditions” (event code 23) with days away from work, by occupation and gender. Repetitive motion conditions include carpal tunnel syndrome, tendonitis and certain strains and sprains. The group most severely affected by this type of injury is quite clearly female machine operators, assemblers and inspectors (RR = 7.3), followed by female handlers, equipment cleaners, helpers and labourers (RR = 7.1).

Table 2. Index of relative risk for repetitive motion conditions with days away from work, by occupation and gender, US nonfarm private industry employees 15 years and over, 1993

Occupation

All

Men

Women

All nonfarm private industry occupations

1.0

0.6

1.5

Managerial and professional specialty

0.2

0.1

0.3

Executive, administrative and managerial

0.2

0.0

0.3

Professional specialty

0.2

0.1

0.3

Technical, sales and administrative support

0.8

0.3

1.1

Technicians and related support

0.6

0.3

0.8

Sales occupations

0.3

0.1

0.6

Administrative support, including clerical

1.2

0.7

1.4

Service occupations1

0.7

0.3

0.9

Protective service2

0.1

0.1

0.4

Service occupations, except protective service

0.7

0.4

0.9

Farming, forestry and fishing occupations3

0.8

0.6

1.8

Precision production, craft and repair

1.0

0.7

4.2

Mechanics and repairers

0.7

0.6

2.4

Construction trades

0.6

0.6

Extractive occupations

0.1

0.1

Precision production occupations

1.8

1.0

4.6

Operators, fabricators and laborers

2.7

1.4

6.9

Machine operators, assemblers and inspectors

4.1

2.3

7.3

Transportation and material moving occupations

0.5

0.5

1.6

Handlers, equipment cleaners, helpers and laborers

2.4

1.4

7.1

1 Excludes private household workers and protective service workers in the public sector
2 Excludes protective service workers in the public sector
3 Excludes workers in agricultural production industries
Note: Long dashes — indicate that data do not meet publication guidelines.
Source: Calculated from the BLS Survey of Occupational Injuries and Illnesses, 1993, and Current Population Survey, 1993.

 

The table shows striking differences in the risk of repetitive motion conditions that depend on the gender of the worker. Overall, a woman is 2.5 times as likely as a man to lose work due to repetitive motion illness (2.5 = 1.5/0.6). However, this difference does not simply reflect a difference in the occupations of men and women. Women are at higher risk in all of the major occupational groups, as well as the less aggregated occupational groupings reported in the table. Their risk relative to men is especially high in sales and blue-collar occupations. Women are six times as likely as men to lose work time from repetitive motion injuries in sales and in precision production, craft and repair occupations.

 

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