Determining whether work-related musculoskeletal problems are apparent and whether job conditions exist that pose a significant risk for such disorders involves different but interrelated data collection methods. As noted in the main text, entries of musculoskeletal problems in company medical records and OSHA Form 200 logs can be tallied for use in calculating incidence and prevalence measures. These measures, in turn, may be compared with those from other departments or those reported for the industry as a whole in making judgments concerning excess cases. The incidence rate (IR) is defined as the number of new cases per 100 worker years (which is equivalent to 200,000 work hours). It may be computed for all musculoskeletal disorders and by disorders of body part (i.e., disorders specific to the wrist, back, shoulders, etc.) The following formula is used in these IR calculations:

IR =	Number of new cases during a time period x 200,000 hr Total hours worked by all workers for that time period

The prevalence rate (PR) calculation is similar, except that all existing numbers of cases for a given time period are used in the formula. Hence,

PR =	Number of all cases during a time period x 200,000 hr Total hours worked by all workers for that time period

Examples of computations of IR and PR are shown in Tray 4–A.

Tray 4–A. Examples of IR and PR Calculations A manufacturer of small electronic products employed an average of 125 full-time production employees—75 working on circuit board assembly tasks and 50 on product assembly tasks. A check of the company medical records in 1994 indicated a total of 20 workers had entries reflecting hand/wrist disorders; 14 of these cases were workers engaged in circuit board wiring; 6 were in assembly work. Medical records for 1995 indicated 5 new cases—4 in circuit wiring board and 1 in product assembly. Calculating the IRs: Five new cases for the total plant were reported in 1995. Time sheets for the workforce indicated a total of 250,000 hours of work time for that year. Thus, the IR for the total plant is: 5 (new cases) x 200,000 250,000 = 1,000,000 250,000 = 4.0 Calculating the PRs: The existing 20 cases of WMSDs noted in 1994 and the 5 new cases for 1995 would indicate a total of 25 cases for the 2-year time period. The total number of work hours time expended by the workforce, based on time sheets for the 2-year time period, equaled 500,000 hours. Thus the PR for the total plant for the 2-year period would be: 25 (existing + new case) x 200,000 50,000 = 5,000,000 500,000 = 10.0

Several different decision rules concerning what constitutes excessive numbers of musculoskeletal problems have been proposed. The following reference suggests that more than one work-related case of musculoskeletal disorders per 200,000 hours or more than a twofold difference in either IR or PR between departments indicates a need for evaluations to determine the basis for the problem:

Kuorinka I, Forcier L eds. [1995]. Health and risk factor surveillance for work-related musculoskeletal disorders. Chapter 5. Work-related musculoskeletal disorders (WMSDs): a reference book for prevention. Taylor and Francis (1900 Frost Road, Suite 101, Bristol, PA 19007).

California is in the process of enacting an ergonomic rule which would require interventions when at least two workers doing the same job develop similar forms of musculoskeletal disorders within a 12-month period (Occupational Safety and Health Standard, Title 8, Chapter 4, Group 15, Article 106, Section 5110, Ergonomics, California Occupational Safety and Health Board, Sacramento, CA, October 1, 1996). For a discussion of decision rules, see Chapter 5 above.

Evidence that excessive numbers of cases of musculoskeletal problems are due to workplace factors will invariably require other forms of data collection. As noted in the main text (Step 4), interviews and questionnaire surveys can furnish added information about the onset and nature of such problems as related to the worker's job. Symptom surveys and special tests can also offer a means for detecting problems that may be missed in more general medical exams and reports. Workers completing a symptom survey form such as shown in Tray 4–B can identify parts of their bodies that are experiencing increased levels of discomfort as a result of poor job design. Although this survey is fairly easy to administer, the following procedures should be followed for best results:

• No names should be required on the forms, and the collection process should ensure anonymity.

• Survey participation should be voluntary in nature.

• Workers should fill out the form on their own (but if needed, the surveys should be administered to groups by a trained person offering explanations).

• The survey should be conducted on work time.

Unless the company is prepared to act on the results of a symptom survey, it should not be conducted. Analysis of the information from a symptom survey is complex. One of the major difficulties is deciding what responses on the questionnaire indicate a problem that may need further evaluation. One approach for scoring results from a survey of this type is to rank-order the number and severity of complaints by body part from the highest to the lowest in frequency and severity. Those jobs linked with the body part showing the most complaints or the highest severity ratings would become the primary candidates for followup efforts at analyzing job risk factors and determining needs for risk reduction measures. A second survey, using the same form, completed after ergonomic changes have been made to correct problem jobs, can indicate whether the intended benefits have been achieved. Comparisons of the worker survey data gathered before and after ergonomic changes can furnish this information. One caution here is to allow sufficient time after the intervention to permit the workers to become accustomed to the job change and allow other novelty effects to subside. The second survey should be made no less than 2 weeks (and preferably 1 month) after the changes and should be made at the same time and day of the week as the initial survey. Comparisons of Monday morning results with those obtained on Friday afternoon may give faulty results because of differences in employee motivation.

The health care professional providing medical services to an employer may use special tests for medical screening or more in-depth diagnostic purposes to confirm suspected cases of musculoskeletal disorders. These may involve the worker moving his or her limbs through a range of motions or various maneuvers, with or without resistance applied by the examiner, to determine whether distinctive signs of pain occur. By pressing their fingers against a body part, examiners can also determine areas of tenderness. Range of motion tests for upper extremity disorders are described in the articles listed in the Health Care Management section of the Toolbox (Tray 8).

Tray 4-B. Symptoms Survey Form

Symptoms Survey: Ergonomics Program

Date ____/____/________

__________ Plant __________ Dept # Job Name______________________________ ________ ______________________ _____ Years _____ Months Shift Hours worked/week Time on THIS Job Other jobs you have done in the last year (for more than 2 weeks) ______ Plant ______ Dept # ______________ Job Name _____months _____weeks Time on THIS Job ______ Plant ______ Dept # ______________ Job Name _____months _____weeks Time on THIS Job (If more than 2 jobs, include those you worked on the most) Have you had pain or discomfort during the last year? [ ] Yes [ ] No (if NO, Stop here) If YES, carefully shade in the area of the drawing which bothers you the MOST. (Complete a separate page for each area that bothers you) Check Area: [ ]Neck [ ]Shoulder [ ]Elbow/Forearm [ ]Hand/Wrist [ ]Fingers [ ]Upper Back [ ]Low Back [ ]Thigh/Knee [ ]Low Leg [ ]Ankle/Foot 1. Please put a check by the word(s) that best describe your problem [ ]Aching [ ]Numbness (asleep) [ ]Tingling [ ]Burning [ ]Pain [ ]Weakness [ ]Cramping [ ]Swelling [ ]Other [ ]Loss of Color [ ]Stiffness 2. When did you first notice the problem?__________(month) __________(year) 3. How long does each episode last? (Mark an X along the line) _____/_____/______/______/______/ 1 hour 1 day 1 week 1 month 6 months 4. How many seperate episodes have you had in the past year?____________________ 5. What do you think caused the problem?________________________________________ ________________________________________________________________________ 6. Have you had the problem in the last 7 Days? [ ]Yes [ ]No 7. How would you rate this promlem? (mark an X on the line) NOW None___________________________________________________________Unbearable When it is the WORST None___________________________________________________________Unbearable 8. Have you had medical treatment for this problem? [ ]Yes [ ]No 8a. If NO, why not? ________________________________________ 8a. If YES, where did you recieve treatment [ ] 1. Company Medical Times in past year ____________________ [ ] 2. Personal doctor Times in past year ____________________ [ ] 3. Other Times in past year ____________________ Did treatment help? [ ]Yes [ ]No 9. How much time have you lost in the last year because of this problem? _____ days 10. How many days in the last year were you on restricted or light duty because of this problem? _____ days 11. Please comment on what you think would improve you symptoms _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________

THIS PAGE WAS LAST UPDATED ON SEPTEMBER 11, 1997