Epidemiology Chp. 4

• Used to project population changes; it is
• affected by the number and age composition of women of childbearing age

• Used for comparisons of fertility among
• age, racial, and socioeconomic groups.

• •Reflects events happening after
• birth, such as congenital malformations, prematurity (birth prior to 28 weeks
• gestation), Low birth weight (<2500 grams)

• •Number of deaths occurring in
• infants less than or equal to 28 days old per total number of live births 

• •Reflects environmental events,
• control of infectious disease and improvement in nutrition.  Relatively stable over time

• •Number of deaths in infants age
• greater than 28 days but less than 365 days old per total number of live births

• •Used to estimate the risk of death
• of the fetus associated with the stages of gestation

• •The number of fetal deaths after 20
• weeks gestation per 1,000 live births plus fetal deaths

Reflects health care access and socioeconomic factors; it includes maternal deaths resulting from causes associated with pregnancy and puerperium (during and after childbirth).

• •Reflects events that occur during
• pregnancy and after birth; it combines mortality during the prenatal and
• postnatal periods

• •The number of deaths to infants
• between 28 weeks gestation to 7 days after birth per 1,000 live births plus
• fetal deaths

•Compares the number of abortions to the number of live births occurring during the same time period

Life Expectancy

•Raw counts

  Number of males

  Number of patients missed  appointments

  Number of cancer deaths

  Number of cases

• Frequency/counts relative to something. 
• Ex. 

 a ratio that consists of a numerator and a denominator and in which time forms part of the denominator.

•Contains the following elements:

–disease frequency

–unit size of population

–time period during which an event occurs

• •Use crude rates with caution when
• comparing disease frequencies between populations.

• •Observed differences in crude rates may
• be the result of systematic factors (e.g., sex or age distributions) within the
• population rather than true variation in rates.

• Specific rates refer to a particular subgroup of the population defined in terms of
• race, age, sex, or single cause of death or illness

• •The value obtained by dividing one
• quantity by another

• •The most general form has no specified
• relationship between numerator and denominator.

• •Proportions, rates, and percentages are
• also ratios.

• •A measure that states a count relative to
• the size of the group.

• •A ratio in which the numerator is part of
• the denominator.

•May be expressed as a percentage.

•Crude death rate

• •Age-sex-race
• specific death rate

• •Cause
• specific death rate

• •Adjusted
• death rate

• •Proportionate
• mortality rate

• •Standardized
• Mortality Ration (SMR)

• •If the observed and expected numbers are
• the same, the SMR would be 1.0, indicating that observed
• mortality is not unusual.

• •An SMR of 2.0 means that the death rate in the
• study population is two times greater than expected.

•Reported Disease Rate

•Hospitalization Rates

•Incidence Rates

•Prevalence Rates

•Attack Rates

•Epidemic Curve

• The number of cases of a notifiable
• disease reported during a specified period of time per 100,000 (crude
• rate).  Age, race, sex specific reported
• case rates may be obtained in the same manner as crude death rates.

• The number of new cases of a disease that
• occur in a group during a certain time period.

• •Describes the rate of development of a
• disease in a group over a certain time period.

–Numerator = the number of new cases.

–Denominator = the population at risk.

• –Time = the period during which the cases
• occur.

• An incidence measure used when members of a population or study group are under observation for different lengths of
• time.

• The number of existing cases of a disease
• or health condition in a population at some designated time.

•Provides an indication of the extent of a health problem.

• •Describing the burden of a health problem
• in a population.

•Estimating the frequency of an exposure.

• •Determining allocation of health
• resources such as facilities and personnel.

• •If duration of disease is short and
• incidence is high, prevalence becomes similar to incidence.

• •Short duration--cases recover rapidly or
• are fatal.

•Example: common cold

• •If duration of disease is long and
• incidence is low, prevalence increases greatly relative to incidence.

•Example: many chronic diseases

Plotting of the frequency of incident cases over time