Comparative Analyses of Three Measures of Concordance between Current and Longest Held Jobs

Orlando Gómez-Marín MSc PhD, Lora E. Fleming MD PhD, William LeBlanc PhD, David J. Lee PhD , Terry Pitman BA, Alberto Caban MPHUniversity of Miami School of Medicine

Departments of Epidemiology & Public Health, and PediatricsFunding provided in part by NIOSH Grant number R01 0H03915; Worker Photographs by Dr David Parker

http://www.rsmas.miami.edu/groups/niehs/niosh/

BackgroundIn occupational epidemiologic research, databases such as death certificates, insurance and hospital records, cancer registries, employment and union records, and licensure records are often the only source of the subject’s occupation and/or industry. Derived from these records, current or most recent occupation and industry have been used by researchers as a surrogate for longest held job (and its exposures), particularly when lifetime work histories are not available. Previous studies have raised the issue of the validity of using current or most recent occupation or industry to represent the longest held job, especially with rapidly changing employment patterns in the US and elsewhere. Several measures of concordance between current and longest held job have been proposed, but an assessment of their performance has not been published.

ObjectiveTo evaluate three measures of concordance between current and longest held job in a large, population-based, representative sample of US workers.

MethodsThe National Health Interview Survey (NHIS), conducted annually by the National Center for Health Statistics (NCHS), is a continuous, multipurpose, and multistage area probability cross-sectional survey of the US civilian non-institutionalized population living at addressed dwellings.

We used combined data from the 1986 NHIS Supplement on Longest Held Job, and the 1988 NHIS Supplement on Occupational Health. Included in the analyses were data on over 49,000 workers, age 18 years and over, in occupational groups with an estimated employment of 100,000 persons or more. There were different sets of occupational categories: 13-category groupings, more refined list of 41 occupations, and a detailed list of 206 occupations. Within each occupation several subgroups were analyzed: Females and Males; Whites, Blacks, and Others; Hispanics and Non Hispanics.

Three measures of concordance were used and compared in terms of their ability to produce similar rankings. The concordance measures used can be defined in terms of the observed cell frequencies a, b, c, and d in a 2x2 table with columns corresponding to recent work (Yes vs No) in a given occupation, and rows corresponding to longest held job (Yes vs No) in the same given occupation, as follows:

• Burnett's index = a/(a + c)• Dice’ s Coincidence Index = 2a/(2a + b + c)• Cohen’s Kappa = (2*[a*d - b*c])/([a+b]*[b+d) + [a+c]*[c+d])

The performance of the above indices, in terms of their ability to produce similar rankings for different sets of occupational categories, and different gender, race, and ethnic subgroups was assessed by the use of Spearman's rank order correlations.

RESULTSComplete data for occupations with an estimated employment of 100,000 persons or more were available for 49,234 participants of the 1986 and the 1988 NHIS Supplements combined. Included were

•23,820 females (48.4%) and 25,414 males (51.6%); •41,556 Whites (84.4%), 6,268 Blacks (12.7%), and 1410 Other Races (2.9%); •3,035 Hispanics (6.2%) and 46,199 non Hispanics (93.8%).

Comparison of the rankings of the occupations showed highly significant values of Spearman Correlation Coefficients ranging from 0.73 for Dice's and Burnett's and also for Kappa and Burnett's indices (p = 0.006), to 0.96 for Kappa and Dice's index (p < 0.001).

Conclusions

High levels of agreement between current and longest held occupation were observed using three different indices. Although not directly comparable, the Kappa and Dice’s indices performance is almost identical and superior to that of Burnett’s index. Because of its known statistical properties and wide availability in most statistical packages, Kappa is the recommended index.

Results of these analyses in terms of additional tables can be obtained from our Study Web page at www.rsmas.miami.edu/groups/niehs/niosh/.

Occupation Sample Cohen's 99% CI for Cohen's Dice's Burnett's [K,D,B] Size Kappa±SE Kappa Kappa Index Index Ranks Professional specialty 49,234 71.2±0.4 [70.2,72.2] 71.2 75.6 73.4 [1,1,1] Farming, forestry, fishing 49,234 64.7±1.0 [62.1,67.3] 64.7 65.8 63.0 [2,3,6] Transportation/ material moving 49,234 62.6±0.9 [60.3,64.9] 62.6 64.1 65.3 [3,5,4] Administrative support occs, including clerical 49,234 61.2±0.5 [59.9,62.5] 61.2 67.5 65.4 [4,2,2] Precision production, craft, repair 49,234 60.1±0.6 [58.6,61.6] 60.1 64.8 62.2 [5,4,8] Protective service 49,234 59.9±1.5 [56.0,63.8] 59.9 60.5 65.4 [6,8,3] Service occs, except protective/household 49,234 58.6±0.6 [57.1,60.1] 58.6 62.8 62.6 [7,6,7] Machine operators, assemblers, inspectors 49,234 57.1±0.7 [55.3,58.9] 57.1 60.5 57.6 [8,7,10] Sales 49,234 54.5±0.6 [53.0,56.0] 54.5 59.3 61.4 [9,9,9] Technicians/related support 49,234 53.0±1.0 [50.4,55.6] 53.0 54.7 53.2 [10,10,12] Private household 49,234 50.6±2.0 [45.4,55.8] 50.6 51.1 55.4 [11,12,11] Executive, administrative managerial 49,234 47.3±0.6 [45.8,48.8] 47.3 53.4 63.5 [12,11,5] Handlers, equipment cleaners, helpers, laborers 49,234 31.7±1.1 [28.9,34.5] 31.7 34.1 30.6 [13,13,13]

Table 1. Three Indices of Concordance Between Current and Longest Held Job for US Workers in 13 broad occupational groups

Figure 1. Scatter diagram for Kappa vs Dice's indices

Table 2. Spearman Rank Correlations for Three Indices of Concordance Between Current and Longest Held Job by Number of Occupational Groups, and Gender, Race, and Ethnic Subgroups.