Cheatography

# Chapter 4 Epidemiology Cheat Sheet by Nvstewart

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 DesignsCasre 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

 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.

### Interq­uartile Data + Box Plot example.

 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;