Harkness2e chap07 ppt

Chapter 7: Describing Health Conditions:

Understanding and Using Rates

Chapter Highlights

• Concept and calculation of rates• Crude, specific, and adjusted rates• Incidence and prevalence rates• Sensitivity and specificity calculations

Rate—the primary measurement used to describe the occurrence (quantity) of a state of health in a specific group of people in a given time period

Epidemiologic Descriptive Studies

• Epidemiologic descriptive studies have determined measurable risk factors for major illnesses.

Question

Is the following statement true or false?Epidemiologic descriptive studies have determined measurable risk factors for major and minor illnesses.

Answer

FalseRationale: Epidemiologic descriptive studies have determined measurable risk factors for major illnesses.

Understanding and Using Rates

• Measuring the magnitude or frequency of a state of health determines the characteristics of those who are at high risk.

• Epidemiologic descriptive studies have determined measurable risk factors for major illnesses.

• Calculation of rates provides the best indicators of the probability that a specific state of health will occur.

How to Calculate Rates

1. All of the events being measured should be included in the numerator.

2. Everyone included in the denominator should be at risk for the event in the numerator.

3. A specific period of time for the observations must be clearly indicated.

4. A rate is a fraction or a proportion; therefore, it is necessary to multiply by a base, usually a multiple of 10, to make the rates understandable. This removes the decimal points and makes the comparison of rates easier to interpret.

Question

Is the following statement true or false?Adjusted rate is the measurement of the occurrence of the health problem or condition being investigated in the entire population.

Answer

FalseRationale: Adjusted rate—statistical procedure that removes the effects of differences in the composition of a population, such as age, when comparing one with another. Crude rate—measurement of the occurrence of the health problem or condition being investigated in the entire population

• Indices of the health of a community, region, or country include comparisons of general mortality rates and maternal infant rates.

• A variety of rates can be calculated according to need, including incidence, prevalence, adjusted, and specific rates.

• Specific rates calculated by person, place, and time provide the best description of a health condition.

Crude and Adjusted Rates

• Adjusted rate—statistical procedure that removes the effects of differences in the composition of a population, such as age, when comparing one with another

• Crude rate—measurement of the occurrence of the health problem or condition being investigated in the entire population

Incidence and Prevalence Rates

• Incidence rate—measure of the probability that people without a certain condition will develop that condition over a period of time

• Prevalence rate—measures the number of people in a given population who have an existing condition at a given point in time

Question

What is the name of the prevalence rate that indicates the existence of a condition during an interval of time, such as a year?A. PeriodB. Periodic changeC. PointD. Rate

AnswerA. PeriodRationale: Period prevalence—a prevalence rate that indicates the existence of a condition during an interval of time, often a year. Periodic change—seasonal or cyclic fluctuations in time surrounding health problems. Point prevalence—a prevalence rate that indicates the existence of a condition at a specific point in time. Rate—the primary measurement used to describe the occurrence of a state of health in a specific group of people in a given time period

Question

Is the following statement true or false?Incidence rate is the measure of the probability that people without a certain condition will develop that condition over a period of time.

Answer

TrueRationale: Incidence rate—measure of the probability that people without a certain condition will develop that condition over a period of time.Incidence density—use of a person–time denominator in the calculation of rates; a person–day reflects one person at risk for 1 day, and a person–year represents one person at risk for 1 year

Types of Incidence Rates

• Incidence density: Use of a person–time denominator in the calculation of rates; a person–day reflects one person at risk for 1 day, and a person–year represents one person at risk for 1 year

• Incidence rate: Measure of the probability that people without a certain condition will develop that condition over a period of time

• Relative risk ratio: The ratio of the incidence rate in the exposed group and the incidence rate in the nonexposed group.

Question

What is the term for the ratio of the incidence rate in the exposed group and the incidence rate in the nonexposed group?A. AdjustedB. RateC. CrudeD. Relative risk ratio

Answer

D. Relative risk ratioRationale: Adjusted rate—statistical procedure that removes the effects of differences in the composition of a population, such as age, when comparing one with another. Rate—the primary measurement used to describe the occurrence (quantity) of a state of health in a specific group of people in a given time period. Crude rate—measurement of the occurrence of the health problem or condition being investigated in the entire population. Relative risk ratio—the ratio of the incidence rate in the exposed group and the incidence rate in the nonexposed group.

Sensitivity and Specificity

• Sensitivity is the ability of the test to identify correctly people who have the health problem under study. It is the probability of testing positive if the health problem is truly present.

• Specificity is the ability of the test to identify correctly people who do not have the health problem. It is the probability of testing negative if the health problem is truly absent.

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