Module 2(epi) and Module 4(phs)- Prevalence & Incidence

What are the two types of data

Qualitative:

• data that describes a characteristic but cannot be measured

Quantitative:

• data that can be measured and validated

What types of data are categorized as qualitative

• Categorical

  • can be separated into discrete groups (including dichotomous)

• Ordinal

  • categorical variables with an implied order

what types of data can be categorized as quantitative

• Discrete

  • a numerical type of data that includes whole, concrete numbers with specific and fixed data values determined by counting

• Continuous

  • can assume any numeric value with an infinite amount of values

examples of qualitative data

• observation notes

• open-ended questions

• documents

• video recordings

• audio recordings

• typically, words

examples of quantitative data

• weight in kg

• age

• centimeters

• distance in kilometers

• feet or inc

• # of weeks in a year

categorical data can be

separated into discrete groups (including dichotomous)

• Gender (Male, Female)

• Brand of soaps

• Hair color

• Yes or No

continuous data can assume any

numeric value with an infinite amount of values

• the height of children

• weight of a truck

• the speed of cars

• gas prices

Ordinal data can have

categorical variables with an implied order

• socioeconomic status (poor, middle class, wealthy)

• education level (hs, bachelors, masters, etc)

discrete data has a characteristic

that varies and can only take on a set number of values (whole numbers)

• number of customers

• number of patients

• number of students

What type of data are the number of patients who went to the emergency room

• quantitative

• discrete

what type of data are eye colors

• qualitative

• categorical

How are epidemiological data reported and presented?

• Measures of central tendency: mode, mean, median

• Measures of variation: range, variance

• Counting and tabulating cases

• Graphical presentations

Counts means what in regards to epi

the total number of persons in a set or a group

• expressed as X

• # of cases of health event

Ratio means what in regards to epi

the values obtained when one quantity is divided by another quantity

• a ratio is expressed as X/Y

• division of one quantity by another

• most general term, includes any expression with a numerator and a denominator

Ratio example

• number of still births compared to live births

• number of diabetics divide by the number of non-diabetics

• number of men in the US who died from a heart attack in 2017 divided by the number of men in the US who died from diabetes in 2017

what is proportion in regards to epi

the numerator is part of the denominator

• proportion = X/(X+Y)

• can be a percentage

• pie charts

what does percentage mean in regards to epi

percentage = A proportion that has been multiplied by 100

• formula is (X/X+Y) x 100

What are the 2 proportions that epidemiologists particularly care about:

• prevalence: health events that currently exist

• incidence: new health events that occur over time

Prevalence

• is a proportion

• tells us how much disease there is in a community

• a snapshot or “still life” picture of population health

• most basic of epidemiologic measures

• includes ALL cases at a given point in time (new and existing)

what is the formula for finding prevalence

answer is always going to be per X

give an example of a point prevalence question

• how many cases of measles on August 1st 2019

give an example of period prevalence

• how many cases of measles in 2019

prevalence will increases if

the duration of the disease is longer or if there is an increase in new cases

prevalence will decrease if

• the duration of the disease is shortened

• high case fatality rate from disease

• improved cure rate of disease

• incidence decreased

Incidence

• Refers to the occurrence of new cases of disease

• incidence is a “motion picture” - describes what is happening in a population as time goes by

• incidence is a measure of the risk of developing disease

• The members of the population who are capable of developing the disease or condition being studied are known as the population at risk

Cumulative Incidence

tells us what proportion of the population gets sick over a specified time period. It is a measure of the risk (probability) of developing disease

what is the formula for cumulative incidence

Cumulative Incidence Considerations

Numerator: Only includes NEW cases, NOT previously existing cases or those currently sick

Denominator: Only includes individuals at risk (of developing the disease)

• should NOT include people with disease or who are NOT susceptible

• pop at risk = total pop minus people w/ the disease or who are immune

Incidence Rate (Incidence Density) formula

Prevalence Summary

• existing cases

• number in total population

• point or period in time to which the prevalence applies

Incidence Summary

• new cases

• population at risk to get the condition

• interval of time to which incidence applies

prevalence formula

Incidence X Duration