Measures of Morbidity and Mortality Used in Epidemiology

C hapter

3

Measures of Morbidity and Mortality Used in Epidemiology Learning Objectives By the end of this chapter the reader will be able to: ●● ●● ●●

●●

●●

●● ●●

define and distinguish among ratios, proportions, and rates explain the term population at risk identify and calculate commonly used rates for morbidity, mortality, and natality state the meanings and applications of incidence rates and prevalence discuss limitations of crude rates and alternative measures for crude rates apply direct and indirect methods to adjust rates explain when either direct or indirect rate adjustment should be used

*Refer to Appendix I for a Chapter 3 worksheet.

Study Questions Instructions: Fill in the blanks with the terms below. attack rate count incidence rate proportion

proportional mortality ratio rate ratio

© 2014 Jones & Bartlett Learning

9781449651589_CH03_FINAL.indd 7

7

10/06/13 12:52 PM

8

C h a p t e r 3 M e a s u r e s

of

Morbidity

and

Mortality

1. A refers merely to the number of cases of a disease or other health phenomenon being studied. (p. 108) 2. A is defined as “the value obtained by dividing one quantity by another.” (p. 109) 3. A is a type of ratio in which the numerator is part of the denominator. (p. 110) 4. Also a type of ratio, a differs from a proportion because the denominator involves a measure of time. (p. 111) 5. The term describes the rate of development of a disease in a group over a certain time period; this period of time is included in the denominator. (p. 118) 6. The is an alternative form of the incidence rate that is used when the nature of the disease or condition is such that a population is observed for a short time period, often as a result of a specific exposure. (p. 120) 7. The is the number of deaths within a population due to a specific disease or cause divided by the total number of deaths in the population. (p. 140)

Ca l c u l a t i o n P r o b l e ms 8. In 2006, a total number of 2,426,264 resident deaths were registered in the United States. The estimated population in the United States as of July 1, 2006, was 299,398,484. a. Define the term crude death rate and give the formula. b. Calculate the crude death rate per 100,000 population. 9. As of June 30, 2009, the estimated population of Swaziland (located in southern Africa) was 1,123,913. The estimated number of deaths as of June 30, 2009, was 34,650. What is the estimated crude death rate per 1,000 population?


9781449651589_CH03_FINAL.indd 8

10/06/13 12:52 PM

Calculation Problems

9

10. The following number of cases of norovirus were reported among employees of a long-term residential treatment facility in Oregon in 2007 (refer to Student Manual Table 3–1): Student Manual Table 3–1 Sex, Number of Respondents, and Number Ill among Employees of Wards with ≥10 Cases,* in a Norovirus Outbreak at a Long-term Residential Treatment Facility—Oregon, October–December 2007 Sex Male Female

Number of Respondents

Number Ill

43 99

12 39

*Based on 146 self-administered, anonymous questionnaires submitted by employees of wards with 10 or more cases; some employees did not answer all questions. Source: Data from Centers for Disease Control and Prevention. Recurring norovirus outbreaks in a long-term residential treatment facility—Oregon, 2007. MMWR. Vol 58, No 25, p. 697. July 3, 2009.

a. Define the term attack rate and give the formula. b. Calculate the attack rates for males and females separately. What was the attack rate for all employees? c. Among the ill respondents, calculate the proportion of male cases. 11. Student Manual Figure 3–1 indicates the prevalence of smoking at 3 months before pregnancy in selected states in the United States during the year 2005.


9781449651589_CH03_FINAL.indd 9

10/06/13 12:52 PM

10


of

West Virginia Arkansas Maine Ohio Oklahoma Alaska Michigan Minnesota Vermont South Carolina Nebraska New York* North Carolina Rhode Island Oregon Hawaii Colorado Georgia New Mexico Illinois Washington Maryland Florida New Jersey New York City Utah

Morbidity

and

Mortality

Average prevalence (22.1%)

0

10

20

30

40

50

Percentage

STUDENT MANUAL FIGURE 3–1 Prevalence of smoking 3 months before pregnancy—Pregnancy Risk Assessment Monitoring System (PRAMS), United States, 26 sites, 2005. Source: Adapted and reprinted from

Centers for Disease Control and Prevention. Trends in smoking before, during, and after pregnancy—Pregnancy Risk Assessment Monitoring System (PRAMS), United States, 31 sites, 2000–2005. Surveillance Summaries. MMWR. Vol 58, No SS-4, p. 10. May 29, 2009.

a. Define the term prevalence. b. Give the formula for point prevalence. c. Interpret Student Manual Figure 3–1, e.g., compare the states with the highest and lowest prevalence of smoking before pregnancy.


9781449651589_CH03_FINAL.indd 10

10/06/13 12:52 PM

Calculation Problems 50

3 or more 2 1

40

Percent

11

26.7

30 16.2

20 11.5

10 0

8.1 2.9 5.5

50–59

5.9

6.6

4.1 7.3

9.3

60–69 70–79 Age (in years)

9.6

80 and over

STUDENT MANUAL FIGURE 3–2 Percentage of adults aged 50 years and over, by age and number of physical limitations: United States, 2001–2007. Source: Reprinted from NCHS Data Brief. Aging differently: Physical limitations among adults aged 50 years and over: United States, 2001–2007. NCHS data brief, No 20. Hyattsville, MD: National Center for Health Statistics, 2009, p. 1.

12. The following information was collected from the National Center for Health Statistics (NCHS) regarding the percentage of adults (aged 50 years and over) with physical limitations (refer to Student Manual Figure 3–2): Which of the following statements is more appropriate based on the figure? a. The prevalence of physical limitations increases with age. b. The risk of physical limitations increases with age. 13. A total of 4,265,555 live births were registered in the United States in 2006. The estimated population of the United States on July 1, 2006, was 299,398,484. a. Define the term crude birth rate and give the formula. b. Calculate the crude birth rate per 1,000 persons in 2006.


9781449651589_CH03_FINAL.indd 11

10/06/13 12:52 PM

12


of

Morbidity

and

Mortality

14. The estimated population of women aged 15–44 years in the United States during 2006 is shown in Student Manual Table 3–2 below. There were 4,265,555 registered births during 2006. a. Define the term general fertility rate and give the formula. b. Calculate the general fertility rate per 1,000 women aged 15–44 years. You will need to calculate the total number of women aged 15–44 by using the data shown in the table. Student Manual Table 3–2. Estimated Number of Women Aged 15–44 Years in the United States as of July 1, 2006, by Age Group Age Group

Number of Women

15–19 20–24 25–29 30–34 35–39 40–44 Total

10,389,322 10,201,150 10,125,210 9,726,116 10,535,872 11,280,796 ?

Source: Data from JA Martin, et al., Births: Final data for 2006. National Vital Statistics Reports. Vol 57, No 7. Hyattsville, MD: National Center for Health Statistics, 2009, p. 95.

15. Student Manual Table 3–3 shows the number of deaths for the five leading causes of death for the total population during 2006 in the United States (estimated population as of July 1, 2006 = 299,398,484). Student Manual Table 3–3 Estimated Number of Deaths for the Five Leading Causes of Death in the United States as of July 1, 2006. Rank Order Cause of Death 1 2 3 4 5

Diseases of heart Malignant neoplasms Cerebrovascular diseases Chronic lower respiratory diseases Accidents (unintentional injuries) All causes

Number 631,636 559,888 137,119 124,583 121,599 2,426,264

Proportional Cause-Specific Mortality Death Rate per Ratio (%) 100,000 26.0 ? ? ? ?

?

Source: Data from MP Heron, et al., Deaths: Final data for 2006. National Vital Statistics Reports. Vol 57, No 14. Hyattsville, MD: National Center for Health Statistics, 2009, p. 5.

a. Define the term proportional mortality ratio and give the formula. b. Calculate the proportional mortality ratio for the second through fifth leading causes of death.


9781449651589_CH03_FINAL.indd 12

10/06/13 12:52 PM

Calculation Problems

13

c. Define the term cause-specific mortality rate and give the formula. d. Calculate the cause-specific mortality (death) rate for diseases of the heart. 16. There were a total of 28,527 registered deaths among children under 1 year of age in the United States in 2006. The estimated number of live births during 2006 was 4,265,555. a. Define the term infant mortality rate and give the formula. b. Calculate the infant mortality rate per 1,000 live births.


9781449651589_CH03_FINAL.indd 13

10/06/13 12:52 PM

9781449651589_CH03_FINAL.indd 14

10/06/13 12:52 PM