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Chapter 4 Epidemiology Cheat Sheet by

A cheat sheet covering the topics in Chapter 4: Study Design and Data Collection for "Introduction to Epidemiology"

Study Design

A program able to lead the researcher on a guided path of analyzing, interp­reting, and system­ati­cally collecting data
There are both analytical and descri­ptive study design forms
Descri­ptive Epidem­iology
Descri­ptive studies are normally followed up with analytical studies, this way one can exam associ­ations that may permit cause-­effect relati­ons­hips.
Involves observ­ation, defini­tions, measur­ements, interp­ret­ations, and dissem­ination of health­-re­lated states or events by using person­,place and time.
Descri­ptive Study Designs
Casre reports: A profile of a single indivi­dual. Includes qualit­ative descri­ptive research of facts in chrono­logical order
Case reports and case series can also suggest the emergence of a new epidemic if disease exceed its expect­ations.
Cross Sectional Surveys: conducted ovver a short period of time [usually a few days or weeks.]
Case series: A small group with similar diagnoses
Explor­atory ecologic designs: making compar­isons between variables using aggregated data on the population level vs the individual level
Ecologic fallacy: an error that results when associ­ation between two variables when the associ­ation does not actually exist.
Excerpt From Introd­­uction to Epidem­­iology Ray M. Merrill;

Multiple ways to Classify Data Examples

Multiple ways to classify Data

Types of data
Nominal Data: unordered catego­ries.
Dichot­omous is nominal data that have two distinct values
Ordinal Data: inform­ation provided by the order among catego­ries. Common in health behavior research
Discrete Data: intergers or counts that differ by fixed amounts, with no interm­ediate values possible
Continous Data: measurable quantities not restricted to taking on integer values.

Measur­emnts of Data

Give an example of ratio?
1 in 6 uninte­ntional deaths are suicides.
How is proportion normally expressed?
As a percentage
Give an example of proportion
123 people were infected, 44 died. Propor­tion: 44/123= 0.36 or 36%
What is Rate?
A Frequency measure that involves nominal data
What is attack rate ?
New cases that start to occur rapidly overtime in a defined population
What is Person­-Time rate also known as?
Incidence Density Rate
What is the difference between mortality rate and incidence rate ?
Mortality rate is deaths occurring during a given time period. Incidence rate is New cases occurring during a given time period
What is the formula for SAR ?
(new cases among contacts of known cases)­/█(­(po­pul­ation at beginning of time period­)-(­primary cases)­(*100)
What is SAR?
Secondary Attack Rate: New rate of cases occurring among known cases
What is point preval­ence?
Existing cases of a disease at a point in time

Other forms of Measur­ements cont'd

Numerical Methods
Measures of dispersion
Arithmetic Mean, geometric mean, Median, Mode
Range, Interq­uartile range, Variance, Standard deviation, coeffi­cient of variation
Measures of Associ­ation
When measuring the associ­ation between two nominal or ordinal variables data is entered into a contin­gency table
When using a contin­gency table all entries are classified by each variable in the table.

Contigency Example:

Interq­uartile Data + Box Plot example.


Age Adjusted Rates

Crude Rate: An outcome Calculated without any restri­ction (i.e gender or age). Crude rates can be calculated for entire popula­tions or in a subgroup
Example: Crude Rate of Motor Vehicle Traffic Fatalities in Califo­rnia, Years 2008–2014
Total Motor Vehicle Traffic Deaths in California from 2008 through 2014 = 21,854
Total Population in California from 2008 through 2014 (summed across years) = 263,81­8,096 Crude Rate = (21,854 ÷ 263,81­8,096) × 100,000 = 8.28 per 100,000 population
Age- adjusted rate: Summary measures adjusted for differ­ences in age distri­butions
Age-ad­justed rates may be preferred for injuries that occur more often among certain age groups than others.
Example: "­fal­l-r­elated deaths are more common among the elderly than any other age group."­
Direct Method = deaths in age group ÷ estimated population of that age group × 100,000.
a given areas age-sp­ecific rate
Indirect Method: a common set of age-sp­ecific rates is applied to the popula­tions whose rates are to be standa­rdized.
Standard Morbid­ity­/Mo­rtality Rate Ratio= SMR
Used less frequently than direct method. SMR=Obser­ved­/Ex­pected.
useful when age-sp­ecific numbers of deaths in the study population are either unavai­lable or small in number (less than 25 events across all age groups, as per Curtin & Klein, 1995).

Other Forms of Measur­emnts used in Public Health

Frequency Distri­bution: complete summary of the freque­ncies, or number of times each value appears.
Other ways to measure data: Bar Charts, steam and leaf plots, box plot, two way scatter plot, line graph, a spot map or area map.
Relative Frequency: dividing the number of people in each group by total number of people.
May normally used for presenting the frequency of nominal, ordinal, discrete, or continuous data.
A histogram shows distri­bution for discrete or continous data
An epidemic curve is a histogram that shows the course of an epidemic by plotting number of cases X time of onset
Excerpt From Introd­uction to Epidem­iology Ray M. Merrill;


Spot/Area Map



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