Chapter 5 Epidemiologic Principles and Methods Definition of Epidemiology • Epidemiology is defined as “the study of the distribution and determinants of disease frequency in human populations.” Step 1: Define the Disease • Death is easy to determine. – A death certificate states cause of death. • A blood test or stool culture is needed to verify a diagnosis of certain diseases. • Some diseases are hard to define. – EMS and SARS. • Sometimes a definition changes as more is learned. – AIDS • Other health outcomes include injuries and risk factors. Disease Frequency • Count the number of people with a disease and relate that to the population at risk (PAR). • PAR (denominator) may be the total population or exposed population, or one gender or age group. – PAR often comes from a census. • Two ways to measure frequency are: – Incidence, the number of new cases. – Prevalence, the number of existing cases. • Incidence is used for studying causes of disease. Disease Frequency, ctd. • Prevalence depends on incidence and prognosis. – If causes or risk factors increase, incidence and prevalence increase. – If ability to diagnose increases, incidence and prevalence appear to increase. • Prevalence rates are most useful in assessing the societal impact of a disease and planning for healthcare services. Distribution of Disease • Who – Sex, age, occupation, race, and economic status • When – Season, year (long-term trends), elapsed time since an exposure (epidemic curve). – Is crucial in tracking an outbreak of infectious diseases such as hepatitis and legionellosis. • Where – Neighborhood (e.g. clusters), latitude (climate), urban vs. rural, national variations. – Looks at comparisons of disease frequency in different countries, states, counties, or other geographical divisions. Determinants of Disease • Why is distribution as it is? • We can make inferences from distribution. • Epidemiologists usually speak of risk factors not causes. Human Population • Epidemiology studies human population, usually using observational rather than experimental methods. • Biomedical approach uses animal models to investigate the causes of disease. • Experiments conducted on animals can yield clear answers as to cause and effect. • For ethical reasons, experiments cannot usually be done on humans. Kinds of Epidemiologic Studies • Goal is to determine an association between an exposure and a disease or other health outcome. • Studies may be prospective or retrospective. • Intervention study • Cohort study • Case-control study Intervention Study • Epidemiologists do not perform the experiments. – Closest thing to an experiment. • Start with two groups: – Experimental group (gets the intervention or exposure) – Control group • Watch them over time and compare outcomes. • Experimenter chooses who is in which group. • Two groups should be as similar as possible so that intervention is the only difference. Intervention Study, ctd. • Randomized, double-blind, placebo control is ideal. • Pharmaceutical companies conduct many clinical trials for new drugs. • Physicians’ Health Study was a prevention study: – Aspirin to prevent heart disease. – Beta carotene to prevent cancer. • Field trial of polio vaccine in 1954 was randomized and double-blind. • Kingston–Newburgh study of fluoridation to prevent tooth decay was a community trial. Cohort Study • Are for situations when doing an intervention study would be unethical or too difficult. – Considered the next most accurate. • Choose a large number of healthy people, collect data on their exposures, and track outcomes over time. • The only difference from intervention is that people choose their own exposures. Cohort Study: Examples • Framingham Heart Study • Nurses’ Health Study • British study of physicians on smoking and lung cancer • Hammond–Horn study on smoking and lung cancer in the U.S. Case-Control Study • Faster and cheaper are the advantages. • This is the least accurate approach. • It is commonly done to follow up on a hypothesis generated by “shoe-leather” epidemiology. • Choose people who already have disease. • Choose a healthy control group of individuals, as similar as possible to cases. • Interview them all and ask for their previous exposures. • Estimate the strength of the association between exposure and disease by calculating an odds ratio. Discussion Question 1 • What is the difference between incidence and prevalence? • Why is incidence more useful in identifying the cause of a disease? • When is it most useful to use prevalence? • Give examples for each. Discussion Question 2 • Explain the interaction between incidence, prevalence, and prognosis. • Give examples. Discussion Question 3 • Why are the who, when, and where questions useful in determining the causes of disease? • Give examples. Discussion Question 4 • Explain the three major types of epidemiologic studies. • Which is most likely to yield a valid result? Why? • Which is likely to yield an answer in the shortest period of time? Why? Discussion Question 5 • Visit the National Institutes of Health website on clinical trials, www.clinicaltrials.gov. – Browse by condition. • How many clinical trials are going on right now? • Choose a condition and investigate what treatments are being tested for that condition. Discussion Question 6 • Visit the website of the Nurses’ Health Study, www.channing.harvard.edu/nhs. • Read the most recent annual newsletter. • What are the most recent findings of this cohort study?
QUALITY: 100% ORIGINAL – NO PLAGIARISM
(USA, AUS, UK & CA PhD. Writers)
CLICK HERE TO GET A PROFESSIONAL WRITER TO WORK ON THIS PAPER AND OTHER SIMILAR PAPERS
About Our Service
We are an online academic writing company that connects talented freelance writers with students in need of their services. Unlike other writing companies, our team is made up of native English speakers from countries such as the USA, UK, Canada, Australia, Ireland, and New Zealand.
- At ClassicWritersBay.com, most of our writers are degree-holding native speakers of English who are familiar with various writing styles. Our writers are proficient in many fields, including Economics, Business, Accounting, Finance, Medicine, Chemistry, Literature, Mathematics, Statistics, and many others.
- Making our customers happy is an important part of our service. So do not be surprised if you get your paper well before the deadline!
- We pay a lot of attention to ensuring that you get excellent customer service. You can contact our Customer Support Representatives 24/7. When you order from us, you can even track the progress of your paper as it is being written!
- We are attentive to the needs of our customers. Therefore, we follow all your instructions carefully so that you can get the best paper possible.
- It matters to us who writes for you, and we are serious about selecting the best candidates.
- Our writers are always learning something new, so they are familiar with the latest developments in the scientific world and can write papers with updated information and the latest findings.
- Quality original papers that follow your instructions carefully.
- On time delivery – you get the paper before the specified deadline.
- Attentive Customer Support Representatives available 24/7.
- Complete confidentiality – we do not share you details or papers with anybody else.