Epidemiology Unit 2

Case-fatality rate

The case-fatality rate is the proportion of persons with a particular condition (cases) who die from that condition. It is a measure of the severity of the condition.

Definition of death-to-case ratio

The death-to-case ratio is the number of deaths attributed to a particular disease during a specified time period divided by the number of new cases of that disease identified during the same time period.

Deviation bar charts

a deviation bar chart displays both positive and negative changes from a baseline. (Imagine profit/loss data at different times.)

Incidence

refers to the occurrence of new cases of disease or injury in a population over a specified period of time.

Cause-specific mortality rate

the cause-specific mortality rate is the mortality rate from a specified cause for a population. The numerator is the number of deaths attributed to a specific cause. The denominator remains the size of the population at the midpoint of the time period.

Continuous variables

can have any value in a range (e.g., amount of time between meal being served and onset of gastro-intestinal symptoms; infant mortality rate).

Box Plot

data are summarized by using "box-and -whiskers." The "box" represents values of the middle 50% (or interquartile range) of the data points, and the "whiskers" extend to the minimum and maximum values that the data assume.

Ordinal variables

do have an intrinsic order, but, again, differences between levels are not relevant. Examples of ordinal variables are "low, medium, high" or perhaps categories of other variables (e.g., age ranges).

Table shells

epidemiologists anticipate and design their analyses in advance to delineate what the study is going to convey, and to expedite the analysis once the data are collected. tables that are complete except for the data. They show titles, headings, and categories.

Discrete variables

have values that are integers (e.g., number of ill persons who were exposed to a risk factor)

Vaccine efficacy/effectiveness (VE)

measured by calculating the risk of disease among vaccinated and unvaccinated persons and determining the percentage reduction in risk of disease among vaccinated persons relative to unvaccinated persons. Vaccine efficacy/effectiveness is interpreted as the proportionate reduction in disease among the vaccinated group

Morbidity Frequency Measures

morbidity has been defined as any departure, subjective or objective, from a state of physiological or psychological well-being.

Nominal measurements

no intrinsic order and the difference between levels of the variable have no meaning. In epidemiology, sex, race, or exposure category (yes/no) are examples of nominal measurements

Definition of proportionate mortality

proportionate mortality describes the proportion of deaths in a specified population over a period of time attributable to different causes. Each cause is expressed as a percentage of all deaths, and the sum of the causes must add to 100%. These proportions are not mortality rates, because the denominator is all deaths rather than the population in which the deaths occurred.

period prevalence

refers to prevalence measured over an interval of time. It is the proportion of persons with a particular disease or attribute at any time during the interval

Point prevalence

refers to the prevalence measured at a particular point in time. It is the proportion of persons with a particular disease or attribute on a particular date

Arithmetic-scale line graphs

shows patterns or trends over some variable, often time. In epidemiology, this type of graph is used to show long series of data and to compare several series. It is the method of choice for plotting rates over time

Definition of prevalence

sometimes referred to as prevalence rate, is the proportion of persons in a population who have a particular disease or attribute at a specified point in time or over a specified period of time.

Decision analysis

systematic method for making decisions when outcomes are uncertain. The basic building blocks of a decision analysis are (1) decisions, (2) outcomes, and (3) probabilities

Crude mortality rate (crude death rate)

the crude mortality rate is the mortality rate from all causes of death for a population

One-variable tables

the most basic table is a simple frequency distribution with only one variable. In this type of frequency distribution table, the first column shows the values or categories of the variable represented by the data, such as age or sex. The second column shows the number of persons or events that fall into each category

Relative Risk

the ratio of risks of disease in exposed group vs risk of disease in NONexposed group

Absolute risk

the risk in a group of people with a certain exposure NO COMPARISON

Semilogarithmic-scale line graphs

this technique is useful for displaying a variable with a wide range of values. The x-axis uses the usual arithmetic-scale, but the y-axis is measured on a logarithmic rather than an arithmetic scale.

Probability

% chance of X occurring

odds

% chance of x occurring/ % chance of x NOT occurring

100% component bar charts

A 100% component bar chart is a variant of a stacked bar chart, in which all of the bars are pulled to the same height (100%) and show the components as percentages of the total rather than as actual values.

Bar charts

A bar chart uses bars of equal width to display comparative data. Comparison of categories is based on the fact that the length of the bar is proportional to the frequency of the event in that category

Decision trees

A decision tree is a branching chart that represents the logical sequence or pathway of a clinical or public health decision

Dot plots

A dot plot uses dots to show the relationship between a categorical variable on the x-axis and a continuous variable on the y-axis.

Forest plots

A forest plot, also called a confidence interval plot, is used to display the point estimates and confidence intervals of individual studies assembled for a meta-analysis or systematic review.

Frequency polygons

A frequency polygon, like a histogram, is the graph of a frequency distribution. In a frequency polygon, the number of observations within an interval is marked with a single point placed at the midpoint of the interval. Each point is then connected to the next with a straight line.

Graphs

A graph (used here interchangeably with chart) displays numeric data in visual form. It can display patterns, trends, aberrations, similarities, and differences in the data that may not be evident in tables.

Grouped bar charts

A grouped bar chart is used to illustrate data from two-variable or three-variable tables. A grouped bar chart is particularly useful when you want to compare the subgroups within a group.

Histograms

A histogram is a graph of the frequency distribution of a continuous variable, based on class intervals. It uses adjoining columns to represent the number of observations for each class interval in the distribution.

mortality rate

A mortality rate is a measure of the frequency of occurrence of death in a defined population during a specified interval. Morbidity and mortality measures are often the same mathematically; it's just a matter of what you choose to measure, illness or death.

Pie charts

A pie chart is a simple, easily understood chart in which the size of the "slices" or wedges shows the proportional contribution of each component part.

Population pyramid

A population pyramid displays the count or percentage of a population by age and sex. It does so by using two histograms — most often one for females and one for males

Definition of proportion

A pro portion is the comparison of a part to the whole. It is a type of ratio in which the numerator is included in the denominator.

Definition of ratio

A ratio is the relative magnitude of two quantities or a comparison of any two values. It is calculated by dividing one interval- or ratio -scale variable by the other.

Scatter diagrams

A scatter diagram (or "scattergram") is a graph that portrays the relationship between two continuous variables, with the x-axis representing one variable and the y-axis representing the other.

Stacked bar charts

A stacked bar chart is used to show the same data as a grouped bar chart but stacks the subgroups of the second variable into a single bar of the first variable.

Tables

A table is a set of data arranged in rows and columns. Almost any quantitative information can be organized into a table. Tables are useful for demonstrating patterns, exceptions, differences, and other relationships. If a table is taken out of its original context, it should still convey all the information necessary for the reader to understand the data

Contingency Table

A two-variable table with data categorized jointly by those two variables

Two-and three-variable tables

A two-variable table with data categorized jointly by those two variables . This type of table is called a two -by-two table and is a favorite among epidemiologists. Two-by-two tables are convenient for comparing persons with and without the exposure and those with and without the disease.

Attributable risk calculation

AR = ((risk of disease in exposed group)-(Risk of disease in unexposed group))/(Risk of disease in exposed group)

Case Fatality Rate or Proportion

Case Fatality Rate or Proportion=(Deaths from X) \ (All cases of X)

Cause Specific Mortality

Cause Specific Mortality=(Deaths from X) \ (Total population where deaths occurred)

We use Odds ratio with Case Control as an estimate of risk

It is a good estimate when we consider these 3 things Cases are representative of the population Controls are representative of population The disease being studied does not occur frequently

ODDS ratio

Odds1/Odds0 (Cohort) Ratio of the odds of development of disease in exposed persons to the odds of development of disease in nonexposed persons (Case Control) Ratio of the odds that the cases were exposed to the odds that the controls were exposed

Creating class intervals

Class intervals should be mutually exclusive and exhaustive, example, age ranges should not overlap --Use principles of biologic plausibility when constructing categories. For example, when analyzing infant and childhood mortality, we might use categories of 0-12 months (since neonatal problems are different epidemiologically from those of other childhood problems), 1-5 years (since these result from causes of death primarily outside of institutions), and 5-10 years (since these may result from risks in school settings) --A natural baseline group should be kept as a distinct category i.e. control --If you wish to calculate rates to illustrate the relative risk of adverse health events by these categories of risk factors, be sure that the intervals you choose for the classes of your data are the same as the intervals for the denominators that you will find for readily available data. --Always consider a category for "unknown" or "not stated."

Crude Death Rate

Crude Death Rate =(Total deaths) \ (Population where the deaths occurred)

A commonly used epidemiologic ratio: death-to-case ratio

Death-to-case ratio is the number of deaths attributed to a particular disease during a specified period divided by the number of new cases of that disease identified during the same period. It is used as a measure of the severity of illness

Definition of incidence proportion

Incidence proportion is the proportion of an initially disease-free population that develops disease, becomes injured, or dies during a specified (usually limited) period of time.

Definition of incidence rate

Incidence rate or person-time rate is a measure of incidence that incorporates time directly into the denominator.

Incident equation

Incidence= (New cases of disease over a period of time) \ (Population where the diseases occurred)

Prevalence

Prevalence= (Cases of disease at a POINT in time) \ (Total population at midyear)

Proportional Mortality Rate

Proportional Mortality Rate=(Total deaths FROM disease x) \ (All deaths during the period)

proportionate mortality

Proportionate mortality is the proportion of deaths in a specified population during a period of time that are attributable to different causes.

Composite tables

To conserve space in a report or manuscript, several tables are sometimes combined into one. For example, epidemiologists often create simple frequency distributions by age, sex, and other demographic variables as separate tables, but editors may combine them into one large composite table for publication.

Definition of rate

a rate is a measure of the frequency with which an event occurs in a defined population over a specified period of time