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PUBLIC HEALTH ASSESSMENT

Evaluation of Exposures in Areas Associated with PAH Contamination

GARDNER-ROUSSEL PARK and DR. NORMAN W. CRISP ELEMENTARY SCHOOL
(a/k/a DR. CRISP SCHOOL/GARDNER ROUSSELL PARK)
NASHUA, HILLSBOROUGH COUNTY, NEW HAMPSHIRE


APPENDIX A: TABLES

Table 1.

Samples from areas of Gardner-Roussel Park not covered with clean soil with at least one PAH above the SQL, Nashua, New Hampshire, November, 2001.
Contaminant Health Comparison Value RH-102 RH-103 RH-123 RH-125 RH-127
Naphthalene 2,800* <0.33† <0.33 <0.33 <0.33 <0.33
2-Methylnaphthalene 2,800‡ <0.33 <0.33 <0.33 <0.33 <0.33
Acenaphthene 8,400* <0.33 <0.33 <0.33 <0.33 <0.33
Fluorene 5,600* <0.33 <0.33 <0.33 <0.33 <0.33
Phenanthrene see below§ 0.74 0.42 <0.33 <0.33 <0.33
Anthracene 140,000* <0.33 <0.33 <0.33 <0.33 <0.33
Fluoranthene 5,600* 1.40 0.84 0.46 0.60 0.62
Pyrene 420‡ 1.20 0.72 0.40 0.53 0.64
Benzo[g,h,i]perylene see below§ <0.33 <0.33 <0.33 <0.33 0.37
Acenaphthylene 300 <0.33 <0.33 <0.33 <0.33 <0.33
Benzo[a]pyrene** 0.1†† 0.61 0.35 <0.33 <0.33 0.48
Benzo[a]anthracene N/A 0.56 0.33 <0.33 <0.33 0.34
Benzo[b]fluoranthene N/A 0.55 0.35 <0.33 <0.33 0.40
Benzo[k]fluoranthene N/A 0.54 <0.33 <0.33 <0.33 0.41
Chrysene N/A 0.71 0.44 <0.33 <0.33 0.48
Dibenzo[a,h]anthracene N/A <0.33 <0.33 <0.33 <0.33 <0.33
Indeno(1,2,3-c,d)pyrene N/A 0.34 <0.33 <0.33 <0.33 0.35
* Environmental Media Evaluation Guide (EMEG) for a 28 kilogram child ingesting 200 mg of soil per day, based on the Minimal Risk Level for intermediate exposure.
† All contaminants are reported in parts per million (ppm). "<" indicates less than the detection limit indicated.
‡ Reference Dose Media Evaluation Guide (RMEG) for a 28 kilogram child ingesting 200 mg of soil per day, based on the EPA Reference Dose.
§ S-1 value from New Hampshire Risk Characterization and Management Policy (RCMP). RCMP screening level for this chemical states that the sum of benzo[g,h,i]perylene, phenanthrene and pyrene must be less than 480 ppm.
S-1 value from New Hampshire RCMP.
** Compounds in bold are carcinogenic PAHs.
†† Cancer Risk Evaluation Guide (CREG) for 1.0x10-6 excess cancer risk.


Table 2.

Samples from areas of Gardner-Roussel Park covered with clean soil with at least one PAH above the SQL, Nashua, New Hampshire, November 2001.
Contaminant Health Comparison Value RH-100 RH105* RH-106 RH-107
Naphthalene 2,800† 2.8‡ 0.660 <0.33 <0.33
2-Methylnaphthalene 2,800§ 1.6 <0.660 <0.33 <0.33
Acenaphthene 8,400† 6.2 1.315 <0.33 <0.33
Fluorene 5,600† 6.7 1.800 <0.33 <0.33
Phenanthrene see below 97 28.00 0.56 2.20
Anthracene 140,000† 20 5.950 <0.33 0.46
Fluoranthene 5,600† 110 37.00 1.20 3.50
Pyrene 420§ 89 29.00 1.10 3.10
Benzo[g,h,i]perylene see below 20 8.300 0.37 0.89
Acenaphthylene 300** 4.5 2.750 <0.33 0.34
Benzo[a]pyrene†† 0.1‡‡ 40 14.00 0.64 1.80
Benzo[a]anthracene N/A§§ 44 12.50 0.50 1.60
Benzo[b]fluoranthene N/A 45 14.00 0.59 1.50
Benzo[k]fluoranthene N/A 31 12.00 0.58 1.70
Chrysene N/A 54 18.50 0.70 2.00
Dibenzo[a,h]anthracene N/A 2 0.810 <0.33 0.37
Indeno(1,2,3-c,d)pyrene N/A 22 8.600 0.36 0.95
* Represents the arithmetic mean for two separate samples.
† Environmental Media Evaluation Guide (EMEG) for a 28 kilogram child ingesting 200 mg of soil per day, based on the Minimal Risk Level for intermediate exposure.
‡ All contaminants are reported in parts per million (ppm). "<" indicates less than the detection limit indicated.
§ Reference Dose Media Evaluation Guide (RMEG) for a 28 kilogram child ingesting 200 mg of soil per day, based on the EPA Reference Dose.
S-1 value from New Hampshire Risk Characterization and Management Policy (RCMP). RCMP screening level for this chemical states that the sum of benzo[g,h,i]perylene, phenanthrene and pyrene must be less than 480 ppm.
** S-1 value from New Hampshire RCMP.
†† Compounds in bold are carcinogenic PAHs.
‡‡ Cancer Risk Evaluation Guide (CREG) for 1.0x10-6 excess cancer risk.
§§ No Health Comparison Value available.


Table 3.

Samples from the grounds of the Dr. Norman W. Crisp Elementary School with at least one PAH above the SQL, Nashua, New Hampshire, November 2001.
Contaminant Health Comparison Value DC-1 DC-5 DC-6 DC-7 DC-9
Naphthalene 2,800* <0.33† <0.33 <0.33 <0.33 <0.33
2-Methylnaphthalene 2,800‡ <0.33 <0.33 <0.33 <0.33 <0.33
Acenaphthene 8,400* <0.33 <0.33 <0.33 <0.33 <0.33
Fluorene 5,600* <0.33 <0.33 <0.33 <0.33 <0.33
Phenanthrene see below§ 1.50 1.80 2.40 0.62 0.45
Anthracene 140,000* 0.35 0.41 0.43 <0.33 <0.33
Fluoranthene 5,600* 2.40 3.20 3.10 0.86 0.70
Pyrene 420‡ 2.20 2.90 2.60 0.74 0.61
Benzo[g,h,i]perylene see below§ 0.53 0.59 <0.33 <0.33 <0.33
Acenaphthylene 300 0.33 0.61 0.39 <0.33 <0.33
Benzo[a]pyrene** 0.1†† 0.97 1.60 1.20 0.41 0.34
Benzo[a]anthracene N/A‡‡ <0.33 1.40 1.10 0.37 <0.33
Benzo[b]fluoranthene N/A 0.97 1.50 1.20 0.38 <0.33
Benzo[k]fluoranthene N/A 0.99 1.50 1.20 0.35 <0.33
Chrysene N/A 1.30 1.90 1.70 0.46 0.41
Dibenzo[a,h]anthracene N/A <0.33 <0.33 <0.33 <0.33 <0.33
Indeno(1,2,3-c,d)pyrene N/A 0.53 0.79 0.42 <0.33 <0.33
* Environmental Media Evaluation Guide (EMEG) for a 28 kilogram child ingesting 200 mg of soil per day, based on the Minimal Risk Level for intermediate exposure.Represents the arithmetic mean for two separate samples.
† All contaminants are reported in parts per million (ppm). "<" indicates less than the detection limit indicated.
‡ Reference Dose Media Evaluation Guide (RMEG) for a 28 kilogram child ingesting 200 mg of soil per day, based on the EPA Reference Dose.
§ S-1 value from New Hampshire Risk Characterization and Management Policy (RCMP). RCMP screening level for this chemical states that the sum of benzo[g,h,i]perylene, phenanthrene and pyrene must be less than 480 ppm.
S-1 value from New Hampshire RCMP.
** Compounds in bold are carcinogenic PAHs.
†† Cancer Risk Evaluation Guide (CREG) for 1.0x10-6 excess cancer risk.
‡‡ No Health Comparison Value available.


Table 4.

Samples from areas of Gardner-Roussel Park not covered with clean soil with levels of cPAHs above the SQL Nashua, New Hampshire, November 2001.
Compound RH-102 RH-103 RH-127
  Conc.* BaP-TE Conc. BaP-TE Conc. BaP-TE
Benzo[a]pyrene 0.61† 0.61000 0.35 0.35000 0.48 0.48000
Benzo[a]anthracene 0.56 0.05600 0.33 0.01650 0.34 0.03400
Benzo[b]fluoranthene 0.55 0.05500 0.35 0.03500 0.4 0.04000
Benzo[k]fluoranthene 0.54 0.00540 <0.33‡ 0.00165 0.41 0.00410
Chrysene 0.71 0.00071 0.44 0.00044 0.48 0.00048
Dibenzo[a,h]anthracene <0.33 0.00000 <0.33 0.00000 <0.33 0.00000
Indeno(1,2,3-c,d)pyrene 0.34 0.03400 <0.33 0.01650 0.35 0.03500
Total BaP-TEF Conc.   0.76111   0.42009   0.59358
* Concentration of contaminant
† All contaminants are reported in parts per million (ppm).
‡ "<" indicates less than the detection limit indicated.


Table 5.

Samples from areas of Gardner-Roussel Park covered with clean soil with levels of cPAHs above the SQL Nashua, New Hampshire, November 2001.
Compound RH-100 RH-105 RH-106 RH-107
  Conc.* BaP-TE Conc. BaP-TE Conc. BaP-TE Conc. BaP-TE
Benzo[a]pyrene 40.0† 40.00 14.0 14.000 0.64 0.6400 1.8 1.800
Benzo[a]anthracene 44.0 4.400 12.5 1.2500 0.50 0.0500 1.6 0.160
Benzo[b]fluoranthene 45.0 4.500 14.0 1.4000 0.59 0.0590 1.5 0.150
Benzo[k]fluoranthene 31.0 0.310 12.0 0.1200 0.58 0.0058 1.7 0.017
Chrysene 54.0 0.054 18.5 0.0185 0.70 0.0007 2.0 0.002
Dibenzo[a,h]anthracene 2.50 2.500 0.81 0.8100 <0.33‡ 0.0165 0.37 0.300
Indeno(1,2,3-c,d)pyrene 22.0 2.200 8.600 0.8600 0.36 0.0360 0.95 0.095
Total BaP-TE Conc.   53.964   2.594   0.808   2.594
* Concentration of contaminant
† All contaminants are reported in parts per million (ppm).
‡ "<" indicates less than the detection limit indicated.


Table 6.

Samples from the grounds of the Dr. Norman W. Crisp Elementary School not covered with clean soil with levels of cPAHs above the SQL Nashua, New Hampshire, November 2001.
Compound DC-1 DC-5 DC-6 DC-7 DC-9
  Conc.* BaP-TE Conc. BaP-TE Conc. BaP-TE Conc. BaP-TE Conc. BaP-TE
Benzo[a]pyrene .97† .9700 1.6 1.600 1.2 1.200 .41 .41000 .34 .34000
Benzo[a]anthracene <.33‡ .0165 1.4 .1400 1.1 .1100 .37 .03700 <.33 .01650
Benzo[b]fluoranthene .97 .0970 1.5 .1500 1.2 .1200 .38 .03800 <.33 .01650
Benzo[k]fluoranthene .99 .0099 1.5 .0150 1.2 .0120 .35 .00350 <.33 .00165
Chrysene 1.3 .0013 1.9 .0019 1.7 .0017 .46 .00046 .41 .41000
Dibenzo[a,h]anthracene <.33 0.000 <.33 0.000 <.33 0.000 <.33 0.0000 <.33 0.0000
Indeno(1,2,3-c,d)pyrene .53 .0530 .79 .0790 .42 .0420 <.33 .01700 <.33 .01650
Total BaP-TEF Conc.   1.1477   1.9859   1.4857   0.50546   0.80155
* Concentration of contaminant
† All contaminants are reported in parts per million (ppm).
‡ "<" indicates less than the detection limit indicated.


Table 7.

Assumptions and calculations of exposure risk on the grounds of Gardner-Roussel Park; exposure concentrations are based on completed exposure pathways before remediation.
Calculation of Cancer Risk Due to Direct Contact with Soil (Oral and Dermal Pathways)
Polycyclic Aromatic Hydrocarbons
Gardner-Roussel Park
Present Exposure Concentrations
ADD = EPC * [(IR * EF * ED * RAForal / AT * BW)+(SA * EF * ED * AF * RAFdermal / AT * BW)] * CF
where:
EPC = soil exposure point concentration (mg/kg)*
IR = ingestion rate (mg/day) †
SA = skin surface area in contact with soil on days exposed (cm2/day)‡
RAF = relative absorption factor (unitless)§
AF = soil-to-skin adherence factor (mg/cm2)¶
EF = exposure frequency (days/year) ‡
ED = exposure duration (years) **
BW = body weight (kg)‡
CF = conversion factor (kg/mg)
Sample EPC mg/kg IR mg/day RAF oral SA cm2/day RAF dermal AF mg/cm2 EF days/year ED years AT days BW kg CF kg/mg ADD mg/kg*dayyCSF (mg/kg#day)-1 LCR
Positive Samples Only 15.28522 200 0.31 3,432 0.01 0.2 160 10 25,550 40 1.0×10-6 1.65×10-6 7.30 1.20×10-5

Notes:
* EPCs calculated from average BaP-TE calculations.
† Ingestion rate specific to EPA recommendations [18].
‡ This measurement is specific to the NH DES Recommendations [19].
§ Oral and dermal RAFs from Risk Assessment Information system [20].
¶ Recommended adherence factor, according to USEPA [21].
** Exposure duration represents the number of years spent at the elementary school.


Table 8.

Assumptions and calculations of exposure risk on the grounds of Gardner-Roussel Park; exposure concentrations are based on completed exposure pathways after remediation.
Calculation of Cancer Risk Due to Direct Contact with Soil (Oral and Dermal Pathways)
Polycyclic Aromatic Hydrocarbons
Gardner-Roussel Park
Present Exposure Concentrations
ADD = EPC * [(IR * EF * ED * RAForal / AT * BW)+(SA * EF * ED * AF * RAFdermal / AT * BW)] * CF
where:
EPC = soil exposure point concentration (mg/kg)*
IR = ingestion rate (mg/day) †
SA = skin surface area in contact with soil on days exposed (cm2/day)‡
RAF = relative absorption factor (unitless)§
AF = soil-to-skin adherence factor (mg/cm2)¶
EF = exposure frequency (days/year) ‡
ED = exposure duration (years) **
BW = body weight (kg)‡
CF = conversion factor (kg/mg)
Sample EPC mg/kg IR mg/day RAF oral SA cm2/day RAF dermal AF mg/cm2 EF days/year ED years AT days BW kg CF kg/mg ADD mg/kg*day CSF (mg/kg#day)-1 LCR
Positive Samples Only 0.46506 200 0.31 3,432 0.01 0.2 160 10 25,550 40 1.0×10-6 5.01×10-8 7.30 3.66×10-7

Notes:
* EPCs calculated from average BaP-TE calculations.
† Ingestion rate specific to EPA recommendations [18].
‡ This measurement is specific to the NH DES Recommendations [19].
§ Oral and dermal RAFs from Risk Assessment Information system [20].
¶ Recommended adherence factor, according to USEPA [21].
** Exposure duration represents the number of years spent at the elementary school.


Table 9.

Assumptions and calculations of exposure risk on the grounds of the Dr. Norman W. Crisp Elementary School.
Calculation of Cancer Risk Due to Direct Contact with Soil (Oral and Dermal Pathways)
Polycyclic Aromatic Hydrocarbons
Dr. Norman W. Crisp School Grounds
ADD = EPC * [(IR * EF * ED * RAForal / AT * BW)+(SA * EF * ED * AF * RAFdermal / AT * BW)] * CF
where:
EPC = soil exposure point concentration (mg/kg)*
IR = ingestion rate (mg/day) †
SA = skin surface area in contact with soil on days exposed (cm2/day)‡
RAF = relative absorption factor (unitless)§
AF = soil-to-skin adherence factor (mg/cm2)¶
EF = exposure frequency (days/year) ‡
ED = exposure duration (years) **
BW = body weight (kg)‡
CF = conversion factor (kg/mg)
Sample EPC mg/kg IR mg/day RAF oral SA cm2/day RAF dermal AF mg/cm2 EF days/year ED years AT days BW kg CF kg/mg ADD mg/kg*day CSF (mg/kg#day)-1 LCR
Positive Samples Only 1.18518 200 0.31 3,432 0.01 0.2 125 7 25,550 28 1.0×10-6 9.98×10-8 7.30 7.29×10-7

Notes:
* EPCs calculated from average BaP-TE calculations.
† Ingestion rate specific to EPA recommendations [18].
‡ This measurement is specific to the NH DES Recommendations [19].
§ Oral and dermal RAFs from Risk Assessment Information system [20].
¶ Recommended adherence factor, according to USEPA [21].
** Exposure duration represents the number of years spent at the elementary school.


Table 10.

Cancer Incidence in ZIP Code 03060*; Nashua, New Hampshire (1994-1998).
Type of Cancer Expected† Observed SMR‡ 95% Confidence Interval
Brain and CNS   male 7 4 0.56 [0.15, 1.43]
female 6 -§ - -
Breast female 155 147 0.95 [0.80, 1.12]
Bronchus and Lung  female 70 73 1.04 [0.82,1.31]
female 64 74 1.15 [0.90, 1.31]
Cervix Uteri female 11 8 0.74 [0.32, 1.46]
Colorectal  female 53 62 1.16 [0.89, 1.49]
female 58 60 1.02 [0.78, 1.32]
Corpus Uteri and Uterus female 30 32 1.06 [0.72, 1.49]
Esophagus  male 6 14 2.26 [1.24, 3.80]
female 2.5 - - -
Hodgkins  female 4 7 1.98 [0.79, 4.10]
female 3 - - -
Kidney and Renal Pelvis  female 13 16 1.20 [0.67, 1.95]
female 9 9 1.02 [0.46, 1.93]
Larynx  female 6 11 1.71 [0.85, 3.06]
female 2 - - -
Leukemia  female 13 18 1.42 [0.84, 2.24]
female 11 6 0.55 [0.20, 1.19]
Liver  female 6 8 1.34 [0.58, 2.64]
female 3 7 2.07 [0.83, 4.30]
Melanoma of Skin  female 21 19 0.89 [0.54, 1.39]
female 17 14 0.81 [0.44, 1.35]
Multiple Myeloma  female 6 8 1.40 [0.59, 2.74]
female 5 4 0.77 [0.21, 1.96]
NHL  female 23 32 1.42 [0.97, 1.20]
female 19 26 1.36 [0.89, 1.99]
Oral Cavity and Pharynx  female 15 9 0.60 [0.28, 1.15]
female 8 10 1.23 [0.58, 2.26]
Ovary female 21 29 1.40 [0.94, 2.01]
Pancreas  female 10 6 0.59 [0.22, 1.29]
female 13 15 1.19 [0.67, 1.96]
Prostate female 134 139 1.04 [0.87, 1.22]
Stomach  female 10 8 0.82 [0.35, 1.61]
female 6 6 0.93 [0.34, 2.03]
Testis male 7 14 1.99 [1.09, 3.34]
Thyroid   female 3 - - -
female 10 7 0.68 [0.27, 1.39]
Urinary Bladder  female 32 35 1.10 [0.77, 1.53]
female 12 17 1.38 [0.80, 2.21]
* ZIP Code 03060 includes what is now 03060 and 03064.
† Expected cases have been rounded to whole numbers for presentation only.
‡ Standardized Morbidity Ratio (SMR) is the ratio of the observed cases to the expected cases.
§ Cases are not displayed if less then 4 cases were reported (noted as -).
Denotes a significant difference from expected at the 5% significance level.


APPENDIX B: FIGURES

Intro map for Gardner-Roussel Park
Figure 1. Intro map for Gardner-Roussel Park.

Division of ZIP code 03060 in 1999 into 03060 and 03064 in Nashua, New Hampshire
Figure 2. Division of ZIP code 03060 in 1999 into 03060 and 03064 in Nashua, New Hampshire.


APPENDIX C: EVALUATING CANCER DATA AND BASIC RATE TERMINOLOGY

Cancer Incidence
Cancer incidence is the number of new cases of cancer, by specific type, that is reported for a particular geographic area over a specific period of time. A review of the cancer incidence for selected cancers, as performed in this health assessment, can help determine whether a community is experiencing greater than normal levels of cancer.

The National Cancer Institute estimates that approximately 8.9 million Americans alive in 1997 hada history of cancer. For men, the lifetime risk of developing cancer is 1 in 2; for women, the lifetimerisk is 1 in 3. About 1.3 million new cases of cancer are expected to be diagnosed in 2002.

Cancer Data Standards
A total of 79 cases were removed from the original data set of 1,113. The data that were excluded include all in situ (non-invasive) cases of cancer (79) in the Nashua ZIP code 03060, except for bladder cancer. Incidence rates for cancer are based on invasive cancers only. Invasive cancers are those tumors that have penetrated the basement membrane of the surrounding tissue. The exception to this is bladder cancer. Nationally, physicians determine the invasiveness of bladder cancer inconsistently. As a result, all diagnoses are analyzed together, including in situ cases.

Cancer Data Limitations
In the analyses performed on health outcome data for the 03060 ZIP code in Nashua, the best and most reliable sources of data were used. However, there are limitations with all data sources for these types of analyses. Therefore, those limitations should be considered when interpreting the data. For example, the data analyses are based on small numbers of cancer cases. It is difficult to thoroughly analyze data when the population is so small. When we see a 50% increase in cases from 2 to 3, it is more difficult to attribute an increase in that one case to any particular exposure than when we see a 50% increase in cases from 200 to 300. It is more likely that we would be able to find similar exposures or patterns of exposure among those 100 extra cases than in any one extra case. Additionally, although the data analysis contained the most recent data available, it is still not always current. Through the New Hampshire State Cancer Registry (NHSCR), data are available 18 months after the close of the calendar year. For example, data for 1999 would become available in June 2001. This delay is due to quality control assurance procedures for the data.

In addition, we don't know the time the person has lived in the community. These data sources donot take into account the mobility of a population. Cancer registry data is based on residence of aperson at the time of cancer diagnosis. This presents problems when trying to establish arelationship between disease and exposure at the ZIP code and county level. Since cancer can take20 years to develop, it is often difficult to associate higher cancer levels with local environmentalexposures. The NHSCR has reciprocal agreements for exchange of case information with the statesof Massachusetts, Maine, Vermont, Rhode Island, Connecticut, New York and Florida.

SEER Comparison
Due to the fact that the 1996 population of Nashua (1996 Office of State Planning estimates 82,285) made up approximately 3.7% of the total state population (1997 Office of State Planning estimates 1,172,709), published cancer rates for the State of New Hampshire were not be used as a comparison since they contained cases for Nashua.

The SEER program began data collection in 1973 and currently contains over 2 million cases. Incidence data derived from SEER are based on 9 geographic regions (Connecticut, Iowa, NewMexico, Utah, Hawaii - the metropolitan areas of Detroit, Atlanta, San Francisco - Oakland, andSeattle-Puget Sound, which make up 9.5% of the total U.S. population [10]. Cancer rates for theUnited States' white population were used as the comparison, because this population was mostconsistent with the demographic information derived by the United States Census Bureau for the cityof Nashua, in which approximately 95% of the population are white [2].

Standardized Morbidity Ratio (SMR) Calculation Methodology
To help determine whether a community is experiencing a greater than expected rate of cancer, cancer statistics can be reviewed. First, it is necessary to verify the number of cases of cancer that actually occurred in the community. This is referred to as the observed cases. Observed cases are found through a cancer registry, in this case, the New Hampshire State Cancer Registry. Next, it is necessary to calculate the expected cases, which are the number of cases that would be anticipated to occur. The expected cases are a mathematical prediction of the number of cases that would be expected in a particular community of interest based on the number of cases that have occurred in a reference population, such as a metropolitan area, a state, or the nation as a whole. Prediction of the expected cases takes into account the age, sex, and race of persons in the community. It assumes that the community of interest's population is similar enough to the reference population that the same proportion of any given cancer will be reflected in the community of interest. In the case of those living in Nashua, the population of the United States (SEER) is used as the reference population.

If the reference population has 1000 persons and 25 cases of cancer, the proportion of cancerin that population would be 25 in 1000 (25/1000) or .025. If the community of interest has apopulation of 100, the method to calculate the expected number of cancers would be to multiplythe population of the community, 100 by .025, the proportion seen in the reference population(100 x .025). The expected number of cancers in the community of interest would be 2.5. Thisnumber would then be compared to the number of cases that were actually observed in thecommunity of interest.

The relationship between the observed and the expected cases is called a Standardized MorbidityRatio (SMR). If the observed number of cases is the same as the expected number of cases, theSMR is 1.0, and the community has neither a measurable increased nor decreased cancer incidence. If the observed number of cancer cases is lower than the expected number, then the SMR is less than1.0, and the community has fewer cases than expected. If the observed number of cancer cases ishigher than the expected number of cases, the SMR is greater than 1.0, and it is possible that thecommunity is experiencing a greater than expected rate of cancer.

Standardized Morbidity Ratio What It Means
= 1.00The number of cases in the community is neither higher norlower than what would be expected based on the number ofcases in the reference population.
< 1.00The number of cases is lower than would be expected based onthe reference population. It is possible that the community ofinterest is experiencing less cancer than would be expected.
> 1.00The number of cases is greater than would be expected based onthe reference population. It is possible that the community ofinterest is experiencing more cancer than would be expected.

Caution should be exercised, however, when interpreting these ratios. The interpretation of aratio depends on both the value of the ratio and the numbers used to compute the ratio. Tworatios can have the same size but be interpreted differently.

For example, a ratio of 150 based in 2 expected cases and 3 observed cases indicates a 50% excess in disease, but the excess is actually only 1 case. However, a ratio of 150 based on 200 expected cases and 300 observed cases represents the same 50% excess in disease, but the ratio is based upon a greater number of cases. When we see a 50% increase in cases from 2 to 3, it is more difficult to attribute an increase in that one case to any particular exposure than when we see a 50% increase in cases from 200 to 300. It is more likely that we would be able to find some simliar exposures or patterns of exposure among those 100 extra cases than in one extra case.

Statistical Tests
A certain amount of variation can be expected when looking at the occurrence of different health conditions in communities, and statisticians have developed methods to address these variations. One method is to calculate a 95% confidence interval (CI) for the SMR. The 95% CI is the range of estimated ratio values that has a 95% probability of including the true ratio for the population. The confidence interval is a statistical measure of the precision of the risk estimate.

"Statistically significant" at the 5% level means that the observed difference is not merely theresult of random fluctuation in the number of observed cases. Statistical significance takes intoaccount, by means of a statistical test, these variations in the populations and the numbers thatare being compared.

For example, if the confidence interval does not include 1 and the interval is below 1, then the number of cases is significantly lower than expected. Similarly, if a confidence interval does not include 1 and the interval is above 1, then there is a significant excess in the number of cases. If the confidence interval includes 1, then the true ratio may be 1, and it cannot be concluded with sufficient confidence that the observed number of cases reflects a real excess or deficit.

As long as the 95% confidence interval contains 1, that indicates that the ratio is still within therange one might expect based on the disease experience of the reference population. However, ifeither the upper or lower bound of the confidence interval is 1, it is considered of borderlinestatistical significance. This means that the ratio is close to being statistically significant andthat the number of cases was either higher or lower than expected.

In addition to the number of cases, the width of the confidence interval also reflects the precisionof the ratio estimate. For example, a narrow confidence interval (e.g., 1.03-1.15) indicates thatthe population's size was sufficiently large to generate a fairly precise estimate of the ratio. Awide interval (e.g., 8.5-45) indicates far less precision, and more uncertainty, in the calculatedratio.

For example: if 45 cases of breast cancer are observed and 50 cases of breast cancer areexpected, the SMR would be 45/50, or 0.90 (a number less than 1, which means there is notan increase in cancer incidence). However, if 50 cases of breast cancer are expected, and 60cases of breast cancer are observed the SMR would be 60/50, or 1.20 - a number greater than1, which means the community might be experiencing a greater rate of cancer than isexpected. To determine whether the increase is statistically significant, look at the confidenceinterval around the SMR. If the 95% confidence interval is (.89 - 1.32), the increase is notstatistically significant because it is possible that the true ratio could be any number in thatrange, including .89 to 1. If, on the other hand, the 95% confidence interval is (1.20 - 1.32),the increase is statistically significant because the confidence interval does not include 1,making it unlikely that the true ratio would be less than or equal to 1 strictly due to random fluctuation.

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