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Occupational Respiratory Disease Surveillance logo

A selected list of terms used on NORMS Occupational Respiratory Disease Surveillance pages.


Age-adjusted Death Rates

For a given year, the age-adjusted rate represents the rate that would have been observed if the age-specific rates for specified age groups had occurred in a population with the same age distribution as that of the standard population question-mark icon. Either the U.S. Year 1940 Standard Population or the U.S. Year 2000 Standard Population may be used as the standard. The specific age intervals used are 0-14, 15-24, 25-34, 35-44, 45-54, 55-64, 65-74, 75-84, and 85 years and older. Rates for the entire United States population and for each gender/race group are age-adjusted separately, using the same standard population. Age-adjusted rates are computed by the direct method. First, the annual age-specific rates for the population of interest are calculated. The product of the age-specific rates and the number in the comparable age-specific group in the standard population equals the expected number of deaths per million population for each age group. The total expected numbers of deaths are then obtained by summing over all age groups. The total expected number of deaths are divided by the sum of the standard population and the resulting quotient is multiplied by 1,000,000 to produce the age-adjusted rate (per million). For any time period, age-specific rates first are computed by dividing the average annual number of deaths in each age group by the corresponding age-grouped, mid-year population in the comparable geopolitical unit. Age-adjusted rates then are computed as described above. For more information, see Age Adjustment [PDF - 122KB].

Age-specific Death Rates

Same as crude death rates question-mark icon except that an age-specific rate typically is calculated for a particular age group, whereas a crude death rate typically is calculated for all decedents regardless of age.



Code Fields

For analytical purposes, each cause of death that is written on a death certificate is converted into an International Classification of Diseases question-mark icon code. There can be as many as 20 causes of death listed on a death certificate. These causes of death are collectively referred to as a field of codes (i.e., a code field). A "Multiple Cause" query in NORMS is directly comparable to the entity axis question-mark icon multiple cause-of-death question-mark icon code-field data published annually by NCHS. An "Underlying Cause" query in NORMS is directly comparable to the underlying cause-of-death question-mark icon code-field data published annually by NCHS. A "Contributing Cause" code-field query in NORMS generates data for the number of decedents where the selected respiratory conditions are a contributing cause-of-death question-mark icon on the entity axis question-mark icon. The 2005 Control Table 1 is one example of the control-table data published annually by NCHS. The entity axis is probably most useful for analyses of single respiratory conditions, and when the effect of other respiratory conditions does not factor into the interpretation of results. The record axis should be used when the interaction effects of multiple respiratory conditions is of concern, and when conducting joint analysis of underlying cause of death data. Refer to "Section IV: Multiple Cause Data" on pages 6-12 of the 1996 mortality documentation available at for additional discussion of the appropriate uses, advantages, and disadvantages of the code fields. Please note that NCHS record axis question-mark icon code-field data are not included in NORMS.

Comparability Ratios

A comparability ratio estimates the difference between a sample of death certificates for which the causes of death have been coded according to the standards of two International Classification of Diseases question-mark icon revisions. NORMS data users should first read the following selected guidelines and methods for determining and applying [PDF - 337KB] comparability ratios when interpreting or analyzing NORMS trend data that span one or more ICD revisions. The preceding sources contain underlying-cause comparability ratios estimated for some of the respiratory conditions included in the NORMS database.

Contributing Cause-of-Death

A condition listed on a decedent's entity axis question-mark icon code field question-mark icon that is not also coded as the underlying cause-of-death question-mark icon for that decedent.

Crude Death Rates

To compute annual cause-specific crude death rates, the total number of decedents with a specified condition in a given year is divided by the population of the same geopolitical unit in the same year. Race-specific, gender-specific, and/or Hispanic origin-specific rates are computed from the appropriate subsets of the data. For any multi-year period, the average annual number of decedents with a specified condition is divided by the mid-year population of the same geopolitical unit.



Entity Axis

This code field question-mark icon includes all of the diseases, injuries, or medical complications, as well as the location (part, line, and sequence) of the information recorded on each death certificate. See Parts 2b and 2f of the Instruction Manuals for classifying multiple cause-of-death question-mark icon data.




Hispanic Origin

NORMS does not include any data for Hispanic origin prior to 1990. Most states began reporting this information on death certificates in 1990, however, it was not until 1997 that all states adopted the practice. The following states did not report Hispanic origin (in the following years):

  • Louisiana, New Hampshire, and Oklahoma (1990)
  • New Hampshire and Oklahoma (1991-1992)
  • Oklahoma (1993-1996)


International Classification of Diseases (ICD)

The most recent ICD was published by the World Health Organization (WHO). It is used to categorize diseases and other health problems. Depending on the condition/disease of interest, occupational respiratory disease mortality data may span one to three revisions of the ICD: ICDA-8 (1968-1978); ICD-9 (1979-1998); and ICD-10 (1999-present). See the table of the occupational respiratory disease ICD codes that are included in NORMS.


Between 1993 and 1999, the 1990 U.S. Bureau of Census (BoC) Index of Industries and Occupations classification system was used for coding death certificate information on the NCHS multiple cause-of-death data files. Most codes and titles in the 1990 system do not differ from the 1980 BoC system used for coding death certificates between 1985 and 1992. All NORMS tables reporting BoC industry (CIC) and occupation (COC) codes and titles, except those listed in Changes in Bureau of Census Industry and Occupation Codes and Titles, follow the 1980 BoC classification system. Refer to the "Technical Appendix for 1995" at for additional information. For a comparison of the 1990 CIC and COC codes with more recent industrial and occupational coding systems, refer to the U.S Census Bureau Codes and Crosswalks Web page. Use the Job Name Finder to search the lists of CIC and COC titles, or to obtain a complete listing.





Multiple Cause-of-Death

NCHS has made available annual public-use multiple cause-of-death data files since 1968. These files contain records of all deaths in the United States (approximately two million annually) that are reported to state vital statistics offices. Each death record includes codes for up to 20 (14 for ICDA-8 data) conditions derived from the "Cause of Death" section of the death certificate form, in two fields: the entity axis question-mark icon, which preserves diagnostic detail for all listed conditions and their placement on the death certificate; and the record axis question-mark icon, which reorders the codes, removes redundancies, and (infrequently) combines some associated conditions. For additional information concerning multiple cause-of-death, see Please note that record axis data are not included in NORMS.


Number of Deaths

The number of deaths for each occupational respiratory condition is the number of individual decedents for which the condition was coded. Since 1999, deaths with underlying-cause International Classification of Diseases question-mark icon code J65 (pneumoconiosis associated with tuberculosis) are included in the underlying cause-of-death question-mark icon tabulations of each specific type of pneumoconiosis (except byssinosis), and for each type of tuberculosis. Similarly, deaths with underlying-cause code J92.0 (pleural plaque with presence of asbestos) are included in asbestosis underlying cause-of-death tabulations. Data are restricted to United States residents, based on state of residence at death. Race is classified as white, black, and all others.



Population Estimates

National population estimates are based on national, state-level, and county-level data from the United States Bureau of the Census (BoC) and from NCHS. Estimates obtained from unmodified intercensal Demo-Detail files were used for 1970-1979 and for 1980-1989. The unmodified 1970 intercensal population estimates were used for 1968-1969 because no other county-level population estimates were available. NCHS bridged-race estimates have been used since 1990: for data years 1990-1999, we used the bridged-race intercensal estimates of July 1, 1990-July 1, 1999 (file names "IcenA1_1.txt", "IcenA1_2.txt", "IcenA1_3.txt", and "IcenA1_4.txt"); for data years 2000-2008, we used the vintage 2008 bridged race postcensal population estimates of July 1, 2000 to July 1, 2008 (file names "pcen_v2008_y00.txt" to "pcen_v2008_y08.txt"); for data year 2009, we used the vintage 2009 bridged race postcensal population estimates of July 1, 2009 (file name "pcen_v2009_y09.txt"); for data year 2010, we used the vintage 2010 bridged race postcensal population estimates of July 1, 2010 (file name "pcen_v2010_y10.txt"). The Census Database query is available for generating the population estimates used in NORMS.

Proportionate Mortality Ratio (PMR)

The data used for PMR analyses are a subset of the NCHS multiple cause-of-death question-mark icon files for which usual industry and occupation codes are available and meet quality criteria set by NCHS. The PMR is defined as the observed number of deaths with the condition of interest in a specified industry/occupation, divided by the expected number of deaths with that condition. The expected number of deaths is the total number of deaths in BoC industry (CIC) or occupation (COC) of interest multiplied by a proportion defined as the number of cause-specific deaths for the condition of interest in all industries and/or occupations, divided by the total number of deaths in all industries/occupations. The PMRs generated by NORMS are internally adjusted by five-year age groups (i.e., 15-19, 20-24, ...), gender, and race (i.e., white, black, and all other). Confidence intervals are calculated assuming Poisson distribution of the data. A PMR greater than 1.0 indicates that there were more deaths associated with the condition in a specified occupation or industry than expected.



Record Axis

This code field question-mark icon is generated by a computer algorithm that interprets and translates the information on the entity axis question-mark icon by removing duplicate codes and contradictory diagnoses, and reorders them alphanumerically. See Part 2f of the Instruction Manuals for classifying multiple cause-of-death question-mark icon data and ACME and TRANSAX. The record axis data are not included in NORMS.


Standard Population

The Standard Population is the distribution of U.S. residents, by age group, for a given year. NORMS weights age-adjusted death rates question-mark icon by the percentage of the census population within each of the following age groups, for either the 1940 or the 2000 Census. For more information, see Age Standardization of Death Rates: Implementation of the Year 2000 Standard [PDF - 260KB].

The standard-million population distribution is used when the selected lower age limit is less than 15
Age Group 1940 Census 2000 Census
Population Proportion
Population Proportion
0-14 250,416 25.04 214,700 21.47
15-24 181,67718.17 138,64613.86
25-34 162,06616.21 135,57313.56
35-44 139,23713.92 162,61316.26
45-54 117,81111.78 134,83413.48
55-64 80,294 8.03 87,247 8.72
65-74 48,426 4.84 66,037 6.60
75-84 17,303 1.73 44,842 4.48
85+ 2,770 0.27 15,508 1.55
Total 1,000,000100.00 1,000,000100.00

The working-age population distribution is used when the selected lower age limit is 15 or older
Age Group 1940 Census 2000 Census
Population Proportion
Population Proportion
15-24 181,67724.24 138,64617.66
25-34 162,06621.62 135,57317.26
35-44 139,23718.58 162,61320.71
45-54 117,81115.72 134,83417.17
55-64 80,29410.71 87,24711.11
65-74 48,426 6.46 66,037 8.41
75-84 17,303 2.31 44,842 5.71
85+ 2,770 0.37 15,508 1.97
Total 749,584100.00 785,300100.00

Statistical comparisons of rates

Methods for statistical comparison of rates are described on pages 111-118 of [PDF - 3,451KB]. NORMS generates standard errors (pages 113-115), when rates are based on 100 or more deaths, for making statistical comparisons between two rates using the normal approximation method (page 116). NORMS also provides 95% confidence intervals based on the normal approximation (page 116) or the gamma method (pages 116-117) for statistical comparisons when one or both rates are based on fewer than 100 deaths.



Underlying Cause-of-Death

This code field question-mark icon is represented by a single International Classification of Diseases question-mark icon code that is assigned by a computer algorithm based on the information found in the "Cause of Death" section of the death certificate provided by the certifier of the death. The World Health Organization (WHO) defines the underlying cause-of-death as (a) the disease or injury which initiated the train of events leading directly to death, or (b) the circumstances of the accident or violence which produced the fatal injury. See Parts 2a and 2c of the Instruction Manuals for classifying underlying cause-of-death data.

U.S. Census Regions

A map of the United States displaying U.S. Census Regions and Divisions (Source:

The Northeast (CT, ME, MA, NJ, NY, PA, RI, VT) includes the New England (CT, ME, MA, RI, VT) and Middle Atlantic (NJ, NY, PA) divisions. New York City (Bronx, Kings, New York, Queens, and Richmond counties) is within the Middle Atlantic Division. The South (AL, AR, DC, DE, FL, GA, KY, LA, MD, MS, NC, OK, SC, TN, TX, VA, WV) includes the South Atlantic (DC, DE, FL, GA, MD, NC, SC, VA, WV), East South Central (AL, KY, MS, TN), and West South Central (AR, LA, OK, TX) divisions. The Midwest (IL, IN, IA, KS, MI, MN, MO, NE, ND, OH, SD, WI) includes the East North Central (IL, IN, MI, OH, WI) and West North Central (IA, KS, MN, MO, NE, ND, SD) divisions. The West (AK, AZ, CA, CO, HI, ID, MT, NV, NM, OR, UT, WA, WY) includes the Mountain (AZ, CO, ID, MT, NV, NM, UT, WY) and Pacific (AK, CA, HI, OR, WA) divisions, however, NORMS does not include the non-contiguous states (AK and HI) in the Pacific Division.





Years of Potential Life Lost (YPLL)

YPLL are calculated using the method described by the Centers for Disease Control (CDC) (MMWR Surveill Summ 1986/35(2S)). YPLL to age 65 may be considered as a loss of years from a traditional working life, while YPLL to life expectancy may be considered as a loss of years from the overall life span. To compute YPLL to life expectancy, the number of deaths in each race/gender age group (the same age intervals used for computing age-adjusted rates) first is multiplied by the difference between the mid-point of the age group and life expectancy for that race/gender age group. Life tables published annually by NCHS are used to determine race/gender life expectancies for categories male, female, white, black, white/male, white/female, black/male, and black/female. The overall U.S. population life expectancy is used for other, other/male and other/female. Starting with 2006 data, origin/race/gender life expectancies are used for Hispanic, Hispanic male, Hispanic female, Non-Hispanic white, Non-Hispanic white male, Non-Hispanic white female, Non-Hispanic black, Non-Hispanic black male, and Non-Hispanic black female categories. To compute YPLL to age 65, the number of deaths in age groups up to and including 55-64 is multiplied by the difference between 65 years and the mid-point of each age group (e.g., 65 minus 20 years for the 15-24 age group). The age-specific YPLLs then are summed over all specified age groups to obtain the total YPLL.

Life-expectancy estimates were obtained from the following sources:
Year Source
1968 [PDF - 1,403KB]
1969 [PDF - 31,877KB]
1970 [PDF - 1,254KB]
1971-1972 [PDF - 4,070KB]
1973 [PDF - 2,247KB]
1974 [PDF - 1,366KB]
1975 [PDF - 1,300KB]
1976 [PDF - 1,323KB]
1977 [PDF - 2,495KB]
1978 [PDF - 2,383KB]
1979 [PDF - 41,116KB]
1980 [PDF - 2,735KB]
1981 [PDF - 39,018KB]
1982 [PDF - 2,644KB]
1983 [PDF - 2,891KB]
1984 [PDF - 3,038KB]
1985 [PDF - 2,328KB]
1986 [PDF - 2,690KB]
1987 [PDF - 3,414KB]
1988 [PDF - 3,388KB]
1989 [PDF - 3,683KB]
1990 [PDF - 3,368KB]
1991 [PDF - 3,561KB]
1992 [PDF - 1,344KB]
1993 [PDF - 1,086KB]
1994 [PDF - 1,089KB]
1995 [PDF - 1,804KB]
1996 [PDF - 186KB]
1997 [PDF - 311KB]
1998 [PDF - 335KB]
1999 [PDF - 1,964KB]
2000-2005 [PDF - 1,161KB]
2006 [PDF - 978KB]
2006 (Hispanic) [PDF - 775KB]
2007 [PDF - 1,501KB]
2008 [PDF - 1,273KB]
2009-2010 [PDF - 909KB]


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