C. Causes of Death

Causes of Death are tracked through the California Department of Health Services, Center for Health Statistics, Office of Vital Records and can provide information taken from death certificates. In this report, two different mechanisms are used to report death rates. The "crude death rate" is obtained by dividing the total number of deaths by the total population at risk, then multiplying by some convenient basis (e.g. 100,000). This allows one to evaluate the impact of death due to all possible effects, including age. A separate measure, the "Age-Adjusted Death Rate" follows a statistical formula which helps remove the confounding effect of different age compositions of different populations. This allows a comparison of populations and helps to identify causes of death which are higher or lower than expected. Caution should always be used when using data from death certificates due to known inaccuracies in the completion of many listed causes of death.

Table 4.13 and Exhibit 4.7 shows a comparison of the annual death rate in Humboldt/Del Norte Counties and California over a five year period, 1991-1995. This is a crude death rate. The higher death rate in the Humboldt/Del Norte region can be attributed in part to the larger percentage of the population in the region who are over 65 years old. Since the risk of dying is primarily a function of age, counties with a larger component of the elderly tend to have a high death rate simply because the risk of dying is determined mostly by age.

Exhibit 4.7: Deaths per 1,000 Population

Source: California Vital Statistics, Public Use Death Files, 1991-1995

However, when the rate of all deaths is age-adjusted, Humboldt County’s rate is still significantly higher than the rest of California as shown in Table S.4.13-1 on the following page. Del Norte County’s age adjusted death rate for all causes falls within the 95% confidence intervals calculated for this rate.

Note: Because all vital statistic rates are subject to random variation, the concept of "95% confidence limits" is used to help determine if variation between rates is within expected ranges or is significantly different. The 95% confidence limits depict the range within which the rate would probably occur 95 out of 100 times, if the data were independently acquired on 100 separate occasions. Thus, in five of those 100 data sets, the rate or percent, would fall outside the limits and would then be considered significantly different.

Table 4.14 compares the top ten causes of death in 1995 in the Humboldt/Del Norte area to causes of death for California. Clearly, Disease of the Heart, Malignant Neoplasms (Cancer), Chronic Obstructive Pulmonary Disease and Cardiovascular Disease (Strokes) are the top causes of death in both Humboldt/Del Norte and California. Note however that two of California’s top ten causes of death are different from what occurs in the region. California’s #7 Cause of Death is AIDS, which ranks #14 in Humboldt/Del Norte, and California #10 Cause of Death is Homicide which ranks #20 in Humboldt/Del Norte.

Table 4.15 and Exhibits 4.8 below compares some of the top causes of death for which National Year 2000 Objectives were established, compared with age-adjusted rates in Humboldt County, Del Norte County and California. Three years of data were aggregated to attempt to provide a large enough number of events to allow for comparison. (Even so, some of these events occurred too infrequently, making the stated rates unreliable because the potential for relative standard error exceeds 30%; these are noted.) Each of these causes of death was selected because health promotion or disease prevention activities have been shown to have a positive impact on lowering the incidence of these causes of death. They represent areas of opportunity to improving a community’s health.

Exhibit 4.8: Age Adjusted Death Rates for Selected Causes of Death Compared with California

Source: California County Health Status Profiles, 1997.

Exhibit 4.8: Age Adjusted Death Rates for Selected Causes of Death Compared with California (cont.)

Source: California County Health Status Profiles, 1997.

With the exception of Unintentional Injuries and Motor Vehicle Crashes in Humboldt County, all other death rates fall within the 95% confidence intervals when compared to California rates. In general, the region appears to be close to achieving many of the Year 2000 National Objectives.

To determine whether the occurrence of deaths due to motor vehicle crashes and unintentional injuries was a region-wide problem or could be further defined, sub-area statistics were evaluated and are presented in Exhibit S.4.8-1. Data Limitation: Causes of death are entered on death certificates using a coding system, the ICD9, which accounts for very detailed causes of death. In Exhibits 4.8, codes for similar causes of death were grouped together to provide a broader understanding of the causes of death. Unfortunately, the data presented below represents a single ICD9 code, thus resulting in different (lower) rates. In addition, this data is not age-adjusted. Despite, these limitations, significant variations between sub-areas are apparent. The Eastern Humboldt sub-area has a significantly higher rate for death due to motor vehicle crashes and unintentional injuries and Southern Humboldt has a significantly higher rate of death due to motor vehicle crash injuries. These represent two areas where opportunities for community or individual educational or prevention efforts could conceivably have a positive impact of the death rate.

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