Epidemiology Chapter 3
The crude death rate is a type of
crude rate
Incidence rate is also called
cumulative incidence
Ratio
defined as "the value obtained by dividing one quantity by another." E.g.- Sex Ratio=ratio of males to females in a population (in other words, number of males per 100 females) -For every female there are 970 males -Sex ratio of certain diseases, like aids mortality, death in females versus death in males
Quantitative terms are useful in epidemiology characterize the occurrence of..
disease, morbidity, and mortality in populations
Proportion indicates how important a ..
health outcome is relative to the size of a group
Epidemiologic measurements aid in
in describing occurrence of morbidity and mortality in populations -Alternative conclusions can be drawn from different measures.
Incidence and Prevalence are
interrelated concepts
Incidence density
is a variation of incidence rate that is used when the time periods of observation of the population vary from person to person. -For studies that have long follow up, participants may drop out of the study. Therefore, participants may be observed for different lengths of time. -Incidence density makes use of all participants' data
Counts are
just plain numbers
Rate can be used to
make comparisons among populations Ex) Rate of HIV infection in 2016
Population at risk refers to
members of the population who are capable of developing the disease or condition being studied
Attack Rate
not very important right now, not a true rate
Counts refer to the
number of cases of a disease or other health phenomenon being studied
Late fetal death rate ( per 1,000 live births plus late fetal deaths)
number of fetal deaths after 28 weeks or more gestation --------------------------------------------------------------- number of live births+number of fetal deaths after 28 weeks or more gestation
Reference population is the
population from which cases of a disease are taken
if Incidence increases..... what else increases
prevalence increases
Adjusted rate age is a factor used in
rate adjustment -Comparing Texas to New York where New York has higher crude mortality rate for heart disease (224.1 per 100,000) than Texas (152 per 100,000). However, adjusted rates were not as different (184.8 per 100,000 in New York and 170.7 per 100,000 in Texas).
Rates are used to measure
risk associated with exposures
Measures of incidence are the measure of...
risk of acquiring a disease
Rate provide information on the
speed of development of disease
Rate differs from a proportion because..
the denominator involves a measure of time
Longer living with the disease the prevalence goes...
up HIV more and more are getting HIV but not leading to AIDS
Can be expressed in terms of any unit size of a population that is convenient which is...
( per 1,000 or per 100,000)
The formula is for percentage / proportion
(A/A+B) x 100
Cumulative incidence ( Incidence proportion) =
(Number of new cases over a time period) _________________________________________________________________________ (Total population at risk during the same time period)
Four measures of morbidity (illness) and mortality (death) are:
- Crude Rates - Case- Fatality rates - Proportional mortality ratio - Cause-specific rates
Cumulative Incidence
when all individuals in the population are at risk throughout the time period during which they were observed
Three types of specific rates
-Cause-specific rates -Age-specific rates -Sex-specific rates
Quantitative terms inlude
-Counts -Incidence -Prevalence
Factors that cause prevalence to decrease:
-Decrease in incidence -Shorter duration of disease- new treatment comes up for any condition, it goes down -In-migration of healthy people -Improved cure rate of disease
Counts are the simplest quantitative measures but can be of immense value in certain situations such as
-Even if one case of Ebola virus or small pox are reported, it would be of public health significance -Case reports of patients with particularly unusual presentations or combinations of symptoms often spur epidemiologic investigations.
Perinatal mortality
-Includes botth late fetal deaths and deaths among newborns -Defined as the number of late fetal deaths after 28 weeks or more gestation plus infant deaths within 7 days of birth divided by the number of live births plus the number of late fetal deaths during a year -Expressed as rate per 1,000 live births and fetal deaths
Factors that cause prevalence to increase
-Increase in incidence -Longer duration of the case -In-migration of cases -Prolongation of life of patients without a cure
Infant Mortality Rate
-Number of infant deaths among infants age 0-365 days during a year divided by the number of live births during the same year (expressed as rate per 1,000 live births) -Related to inadequate health care and poor environmental conditions -Substantial racial and ethnic variations
Crude birth rate
-Number of live births during a specified period such as a year per the resident population during the midpoint of the year -Affects the size of the population Crude birth rate= Number of live births within a given period x 1,000 population -------------------------------------------------------------------- Population size at the middle of that period
Fertility Rate
-Number of live births reported in an area during a given time interval divided by number of women age 15-44 years in the area -Expressed as rate per 1,000 women age 15-44 years
Prevalence's variations include
-Point prevalence -Period prevalence -Lifetime prevalence
Epidemiologic measures provide the following types of information
-The frequency of a disease or condition, pattern of the disease -Associations between exposures and health outcomes- -lung cancer with smoker, associate both -Strength of the relationship between an exposure and a health outcome
Crude rate equation
-The numerator consists of the frequency of a disease over a specified period of time. -The denominator is a unit size of population. -Includes a time period during which an event occurred. Aids in making comparisons, but has limitations.
If number of deaths from AIDS among males= 450,451 Number of deaths from AIDS among females=89,895
.833, x 100 = 83%, figure it out
Question for crude rate Number of deaths in the United States during 2013 = 2,596,993 Population of the United States as of July 1, 2013 = 316,128,839
= 821.5 per 100,000
Cause- Specific Rate
A measure that refers to mortality (or frequency of a given disease) divided by the population size at the midpoint of a time period times a multiplier. E.g.- Cause Specific Mortality Rate
Incidence Rate
A rate formed by dividing the number of new cases that occur during a time period by the number of individuals in the population at risk
Adjusted Rate
A rate of morbidity or mortality in a population in which statistical procedures have been applied to permit fair comparisons across populations by removing the effect of differences in the composition of various populations.
Crude Rate
A type of rate that has not been modified to take account of any of the factors, such as the demographic makeup of the population, that may affect the observed rate.
Proportion ( More Specific)
A type of ratio in which the numerator is part of the denominator
Period Prevalence
All cases of a disease within a period of time Example: Percentage of people in the U.S who had asthma during the past 12 months of any particular year
Point Prevalence
All cases of a disease, health condition, or deaths that exist at a particular point in time relative to a specific population from which the cases are derived Example: People with asthma at the time of interview
Lifetime prevalence
Cases diagnosed at any time during the person's lifetime Example: Lifetime Asthma Prevalence
Specific Rates
Is a statistic that refers to a particular subgroup of the population (such as race, age, or sex) or to a particular cause of death or illness.
Proportional mortality ratio (PMR)
Mortality due to a specific cause during the same period --------------------------------------------------------------- x 100 Mortality due to all causes during the same period
What is the difference between Mortality Rate and Case Fatality Rate? Assume a population of 50,000 people of whom 20 are sick with disease X, and in 1 year, 8 of the 20 die from disease X. What is the mortality rate from disease X? What is the case fatality rate from disease X?
Mortality rate from disease X= (8/50,000) * 100 = 0.016% Note: If I had used a multiplier of 1000, the answer would be 0.16 per 1000 Case Fatality rate from disease X= (8/20)* 100 = 40%
Cause specific equation rate =
Mortality( or frequency of a given disease) ----------------------------------------------- x 100,000 Population size at midpoint of time period
Proportion of death from AIDS in males
Number of death from Aids in MALES ------------------------------------------------------------- Number of deaths from AIDS in MALES and in FEMALES
Case fatality Rate
Number of deaths due to a disease that occur among persons who are afflicted with that disease -Measure of lethality of a diseae
Crude rate equation is
Number of deaths in a given year ------------------------------------- Reference populations (during midpoint of the year)
Age specific rate equation =
Number of deaths in a particular age stratum -------------------------------------------------- x100,000 Number of persons within that age stratum (during a time period)
Sex-specific death rate equation=
Number of deaths in a sex group -------------------------------------- x 100,000 Total number of persons in that sex group (during a time period) In the U.S. during 2013, there were 1,496 deaths due to malignant neoplasms among the age group 15-24 years, and there were 43,954,402 persons in the same age group. -Calculate age-specific malignant neoplasm death rate in the age group 15-24 years In 2013, number of deaths among males was 1,308,034. Estimated number of males in the population as of July 1, 2013, was 155,651,602. -Calculate sex-specific crude death rate for males in 2013 per 100,000 Answers -Age-specific malignant neoplasm death rate in the age group 15-24 years= (1,496/ 43,954,402) x 100,000 = 3.4 per 100,000. Sex specific crude death rate for males in 2013 was (1,308,034/155,651,602) × 100,000 = 839.1 per 100,000
Rate= equation which is??
Number of events/ Average population in 2016
Fetal Death rate( per 1,000 live births plus fetal deaths)
Number of fetal deaths after 20 weeks or more gestation --------------------------------------------------------------- x1,000 Number of live births+ number of fetal deaths after 20 weeks or more gestation
Infant Morality rate equation =
Number of infant deaths among infants age 0-365 days during the year x 1,000 live births -------------------------------------------------------------------- Number of live births during the year -Neonatal and post-neonatal mortality rate are related measures.
Perinatal mortality rate equation=
Number of late fetal deaths( after 28 weeks or more gestation)+ infant deaths within 7 days of birth ------------------------------------------------------------ x 1,000 l Number of live births + number of fetal deaths
General fertility rate equation =
Number of live births in a year ----------------------------------- x1,000 women age 15 to 44 Number of women age 15 to 44 years Number of women in this age group at the midpoint of the year
Incidence rate equation =
Number of new cases over a time period x multiplier (e.g., 100,000)///// Average population at risk Multiplier= it makes the values look biger, put correct unit of multi per per 100,000 Cases of uterine cancer in 2016/ Average population of females in 2016
Point prevalence equation =
Number of persons ill at a point in time --------------------------------------------------------- Total number in the group
Case fatality rate equation
Numbers of deaths due to disease "X" during a time period ------------------------------------------------------------------ Number of cases of disease "X" during the same time period
Epidemiologic rates are composed of-
Numerator: Number of health Events Denominator: Population in which events occur A measure of time (time period during which events occur)
Incidence
Refers to the occurrence of new disease or mortality within a defined period of observation (e.g., a week, month, year, or other time period) in a specified population new cases, referring to new cases Incidence rate incidence density
Sex-Specific Rate
The frequency of a disease in a gender group divided by the total number of persons within that gender group during a time period times a multiplier
Age- Specific rate
The number of cases per age group of population during a specified time period Help in making comparisons across age groups
Proportional Mortality Ratio
The number of deaths within a population due to a specific disease or cause divided by the total number of deaths in the population (and multiplied by 100) It is the proportion of all deaths that can be attributed to a given cause
Prevalence
The number of existing cases of a disease or health condition, or deaths in a population at some designated time
Fetal Mortality
Death of the fetus when it is in the uterus and before it has been delivered
Maternal Mortality
Encompasses maternal deaths that result from causes associated with pregnancy. Number of deaths assigned to causes related to childbirth x 100,000 live births (during a year) --------------------------------------------------------------------- Number of live births (including multiple births)
Perinatal Mortality equation problem
In the U.S. during 2015, there were 23,440 deaths among infants under 1 year of age and 3,932,181 live births. -Calculate the infant mortality rate. During 2013, there were 62,939,772 women age 15 to 44 in the U.S. There were 3,932,181 live births. -Calculate the general fertility rate. Answers : Infant Mortality rate= (23,440/3,932,181) × 1,000 = 5.96 per 1,000 live births General Fertility rate= (3,932,181/62,939,772) x 1,000 = 62.5 per 1,000 women age 15 to 44.
Calculation of Incidence Rate: Incidence Rate of Whooping Cough: Number of new cases in U.S., 2013 = 28,639 Average population, July 1, 2013 = 316,128,839
Incidence rate= 9.1 per 100,000 - You get 9.05 ... e^-5, rount to 9.1
PMR Question In the U.S., there were 611,105 deaths due to diseases of the heart in 2013 and 2,596,993 deaths due to all causes in that year. What was the Proportional Mortality Ratio for the diseases of heart in 2013?
PMR = (611,105/2,596,993) × 100 = 23.5%
A Proportion could be expressed as a
Percentage
Incidence and prevalnce
Prevalence = Incidence x Duration of Disease
Types of Ratios
Proportion Percentage Rate
Also a type of ratio
Rate
Percentage
a proportion that has been multiplied by 100
