general terms 1

general terms

Case: People who afflicted with a disease. Risk: A statement of the likelihood of developing a disease or some health problem it measured by rate.Types of risk factors:1. Environmental: physical, drugs, infectious agents, pollutants…2. Behavioral (life habit): as smoking, anxiety.3. Social: include divorce, death of a family member, poverty, & job loss. 4. Genetic : e.g. familial hypercholesterolemia which increase risk of coronary artery disease.Population at risk: It is a frequent term in epidemiology that denotes to the sharing of a characteristic (biological, environmental, socio-economical ) by certain population subgroup that put them at increased risk for development of a health problem (disease, death…), so the population at risk should be susceptible, and exposed to be at risk.

Epidemiology is divided into descriptive & analytic:

Descriptive: It describes the disease phenomena in the population in the term of some variable that gather this population in this variable. The factors that take in consideration in describing most models are: 1- Person, place, time. 2- Host, agent, environment. Analytic: This model answers three most important question in the epidemiology which are: 1- Who is diseased? 2- When does this disease occur? 3- Where does this disease prevalent?

Epidemic: The occurrence of any disease at a frequency that unusual ( compared with baseline data) or unexpected. Outbreak: Unexpected disease occurrence on a local area in short period, for example cases of measles in a school. Endemic: Disease that is occurring regularly in a define population (usual occurrence of a disease). Pandemic (world wide epidemic): An outbreak of disease of a wide geographical area such as a continent. Epizootic: An outbreak (epidemic) of disease in an animal population often with implication). That may effect human population. Epornithic: An Outbreak epidemic of disease in birds population.

Epidemiology Measurement

Categories of measurement: 1:Rate. 2:Ratio. 3:Proportion. Rate: The frequency (number) of events that occur in a defined time period divided by the average population at risk, as X/Y x K per unit of time. Ratio: Expresses a relation between a numerator (X) and a denominator (Y) in which events or items counted a (X) are not derived from (Y) as male/female= 2/1. Proportion: An expression in to the numerator is always included in the denominator, as Y/(X+Y).

*Classification of measurements:

A: Morbidity measurements: Rate of illness in population, include incidence and prevalence. B: Mortality rate: Include crude death, and case fatality. C: Natality rate.

Morbidity rates:

A.1. Prevalent rate: Measures the frequency of all current cases (old and new) of population at risk at specified time. Usually used in chronic diseases. There are 2 types of prevalence: 1. Period prevalence: The number of cases (old & new) of the disease that is present within a period of time ( months, year, season, e.g. for year period from 1999-2005). 2. Point prevalence: The number of cases (old & new) of the disease that is present at a certain point in time. Prevalent rate = All cases of a disease at a given time X 10 n Total population (at risk at a given time) A.2. Incidence rate: Measures the frequency of a new event (disease) or health problem in population at risk during specified period of time. Usually used for acute diseases. Incidence rate =Number of new disease (cases) in specified time X 10 n Number of population exposed to risk during this period A.3. Attack rate: Number of cases of condition out of number of persons exposed. Prevalence= Incidence X Duration



Types of variables: Variable is any item that takes any different values at different person e.g. age, gender, weight, height, blood urea,…1. Qualitative: can not be measured in the usual sense but can be categorized e.g. socio-economic status.

2. Quantitative: can be measured in the usual sense e.g. age, height. It is subdivided into: 2.a. Discrete: Characterized by gaps or interruptions in the value that can be assumed (this type can not assume fractions), e.g. number of human( we can`t say 1.5 human).


2.b. Continuous: Does not have such gaps or interruptions, e.g. height, weight( as 45.5). Population: Large collection of entities or values of a random variable from which we have an interest of variable for a particular time.

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