Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
26 Cards in this Set
- Front
- Back
|
What is Epidemiology |
THE STUDY OF THE DISTRIBUTION AND DETERMINANTS OF DISEASES AND HEALTH RELATED EVENTS IN SPECIFIED (HUMAN) POPULATIONS, AND THE APPLICATION OF THIS STUDY TO THE CONTROL OF HEALTH PROBLEMS |
|
|
Objectives of epidemiology |
•Quantify burden (of disease or health related events) and describe pattern of occurrence – Descriptive Epidemiology •Search for “cause” - Inferential/ Analytical/Observational Studies•Assess control options – Interventional/ Experimental Studies |
|
|
Major groups of basic study design in epidemiology |
1. Descriptive Epidemiology: to study the distribution of health problem 2. Analytic Epidemiology: to study the determinants of health problem •Observational •Interventional/Experimental |
|
|
Descriptive epidemiology |
Assesses variation in the frequency (distribution) of disease in terms of person, place, and time. •Person – age, sex, occupation, income, ethnicity, socioeconomic status, marital status •Place – urban/rural, home/work place, regional variation (disease belts) •Time – short term trend, seasonal or cyclic trend, long term or secular trend |
|
|
Types of descriptive studies |
•Case report •Case series •Correlative studies •Cross sectional studies |
|
|
Case report |
A careful and detailed report of a single patient by one or more physician e.g the progress of symptom and sign (thalidomide story), response of treatment |
|
|
Case series |
The expansion of case report, usually describes the characteristics of a number of patients e.g distribution of cancer by age group, sex and occupation |
|
|
Correlational studies |
Objective: to correlate general characteristics of population with health problem frequency during the same period of time; within the same population at different point in time
Unit analysis is group |
|
|
Cross sectional study |
Objective: ~to examine health problem or disease frequency ~to examine association between the exposure and health problem or disease frequency
Unit analysis is individual Exposure and disease status of individual is assessed at the same time |
|
|
Advantages of cross sectional study |
•A short term study. •Provides information about prevalence (existing burden of disease). •It starts with a reference population, thus making generalization possible. |
|
|
Disadvantages of cross sectional study |
•Provides very little information about the natural history of disease. •Provides very little information about the rate of occurrence of new cases (incidence). |
|
|
Analytic epidemiology |
Attempts to provide the why? and how? of health related events. 1. Observational studies •Case control studies •Cohort studies 2. Experimental studies •Randomized controlled trials (RCT) •Field trials/Community trials •Natural experiment |
|
|
Case Control studies |
These are studies in which comparison are made between individuals who have a disease (cases) and individuals who do not (controls). Exposure status is determined by looking backwards in time (retrospective studies). Exposure and outcome occurred before the start of the study. It proceeds backwards from effect to cause. Objective: Compare risk factors in diseased and non-diseased individuals to determine possible associations. Many outbreak investigations use this study design |
|
|
Steps in conducting a Case Control study |
•Select population •Select cases that meet the disease case definition •Select non-diseased individuals from the population to act as controls/matching •Gather previous exposure/risk factor histories from both groups |
|
|
Strengths of Case Control study |
•Cheap •Quick •Good for rare events/diseases •Multiple exposure can be examined •No attrition •Minimal ethical issues |
|
|
Limitations of Case Control study |
•Study one event at a time •Cannot estimate event risk •Inefficient for evaluation of rare exposures •Does not provide evidence of causation •Potential for bias eg recall |
|
|
Cohort study |
A ‘cohort’ is a group of people who share a common experience or condition. An aetiologic study to investigate the association between some factor and disease. Cohorts are identified prior to the disease under investigation. Study group identified are observed over a period of time to determine disease occurrence among them. Study proceeds forward from cause to effect. |
|
|
Steps in conducting a Cohort study |
•Select a study population free of the disease in question •Select groups stratify in terms of the factor being investigated •Follow up the individuals for a given period of time •Compare the incidence of the disease in each group |
|
|
Strengths of Cohort study |
•Can investigate several diseases at once •Information is reliable •Absolute risk can be obtained •Provides strong evidence of causation •Efficient for evaluation of rare exposures. |
|
|
Limitations of Cohort study |
•Large number of individuals are needed especially when disease is rare •Long time period needed for follow up, hence potential for attrition •expensive |
|
|
Use of two by two tables |
Calculate association between disease and exposuread/bc = Odd Ratio; Relative Risk =a(a+b)/c(c+d) |
|
|
Odds ratio interpretation |
OR = odds of exposure among ill/odds of exposure among well•If OR(RR) > 1, then the exposure is a risk factor for being ill•If OR < 1, then the exposure is protective of illness•If OR = 1, then there is no association between exposure and illness•OR can NEVER be negative! |
|
|
To show a valid statistical association, we need to assess |
•Bias: whether systematic error has been built into the study design•Confounding: whether an extraneous factor is related to both the disease and the exposure•Role of chance: how likely is it that what we found is a true finding |
|
|
Bias |
This is a Systematic error built into the study design.•Selection Bias•Information Bias |
|
|
Types of selection bias |
1. Berksonian bias – There may be a spurious association between diseases or between a characteristic and a disease because of the different probabilities of admission to a hospital for those with the disease, without the disease and with the characteristic of interest 2. Response Bias – those who agree to be in a study may be in some way different from those who refuse to participateVolunteers may be different from those who are enlisted |
|
|
Types of Information bias |
1. Interviewer Bias – an interviewer’s knowledge may influence the structure of questions and the manner of presentation, which may influence responses2. Recall Bias – those with a particular outcome or exposure may remember events more clearly or amplify their recollections3. Observer Bias – observers may have preconceived expectations of what they should find in an examination4. Loss to follow-up – those that are lost to follow-up or who withdraw from the study may be different from those who are followed for the entire study5. Hawthorne effect – an effect first documented at a Hawthorne manufacturing plant; people act differently if they know they are being watched6. Surveillance bias – the group with the known exposure or outcome may be followed more closely or longer than the comparison group7. Misclassification bias – errors are made in classifying either disease or exposure status
|
