Epidemiology Midterm Review- peer

*2x2 table

(ignore parentheses) -a= exposure, diseased -b= exposure, no disease -a+b= total exposed -c= no exposure, disease -d= no expose, no disease -c+d= total not exposed -a+c= total diseased -b+d= total not diseased

case report descriptive study

-case reports are also called series -very specific -information on one person or small number of persons, often first notice of disease, derived most often from clinical practice -ex: start of the HIV/AIDS epidemic in NY and San Fransisco

ecological or correlational descriptive study

-examines information at the aggregated population level only. -correlational examines how two things relate -differences between populations can be described but the etiology cannot be established -ex: correlation between fat consumption and breast cancer mortality by country

descriptive studies

-involves observation, definitions, measurement, and interpretations of health events/states -provide basic information for the allocation of health resources for prevention and care -provide the initial information base for hypothesis generation and analytic study design parameters -three types: ecological or correlational, case reports or series, cross-sectional

Relative Risk or Risk Ratio (RR)

-measure of association -can only do with cohort and clinical trials -indicates the likelihood of disease in the exposed group 'relative' to the unexposed in the study -[a/(a+b)]/[c/(c+d)]= incidence (exp)/ incidence (unexp)= RR -cumulative incidence in exposed/ cumulative incidence in unexposed -"in the study people with the exposure were 2 times more likely to experience disease than those without exposure"

Odds Ratio (OR)

-measure of association -indicates the 'odds' or likelihood of exposure for cases/diseased 'relative' to the controls/non-diseased in the study -(ad)/(bc) -odds an event occurring in one group to the odds it occurring in another group -"in the study, persons with disease were ~2.5 times more likely to have had exposure than those without the disease" -(used with case-control?)

case-control analytical study

-retrospective, observational design, testing a hypothesis -determine group (case/control) membership on the base of whether an individual meets a case definition (meaning they have the outcome of interest) -leaves potential for bias -"either did it or didn't" -ex: study done to determine if aspirin use in children is associated with development of Reye's syndrome, children with/without syndrome are recruited, parents/medical records were used as sources for use of aspirin to establish exposure

cohort analytical study

-used to test specific hypothesis and relationships between disease development or outcome and its determinants -subjects recruited on the basis of their exposure and followed until development or outcome -need to determine whether or not they already have the problem -large samples are needed -ex: Framingham

Relative Risk

A measure of association calculating the risk of an outcome in subjects exposed to a risk factor and comparing that to the risk of an outcome in subjects not exposed to the same risk factor. Calculated by dividing the incidence rate of disease in exposed subjects by the incidence rate of disease in non-exposed subjects.

Odds Ratio

A measure of association used to identify the frequency of exposure and the frequency of outcome in cases and quantify that relationship against control data.

A study was undertaken to test the hypotheses that chewing tobacco increases the risk of stomach cancer. Detailed historical data on chewing tobacco use were collected from 400 subjects with stomach cancer and compared to the same historical data from matched subjects. The results revealed that chewing tobacco was not a significant risk facor for stomach cancer.

Case control

Case Control

Compares (matches) two groups to identify probable causes of a rare disease

When setting up a 2 x 2 table for a case-control study, how do you label your table 1. to the left of cell A and 2. above cell A

Exposure of interest (what you are solving for) 2. Cases with the outcome of interest

When setting up a 2 x 2 table for a cohort study, how do you label your table 1. to the left of cell A and 2. above cell A

Exposure of interest (what you are solving for) 2. Those with the outcome of interest

Prospective Cohort

Follows a group of subjects over time, first collecting baseline health data and exposure information, then investigates, usually over years, as the outcomes manifest.

Cross-Sectional

Good for estimating the prevalence of an exposure or disease in a population at one specific point in time.

Cohort

Good for identifying the effects of a rare exposure

Experimental

Good for proving an association between an exposure and an outcome

Strengths of case control studies include

Good for rare diseases with long latent periods, outbreak investigations, and are relatively inexpensive

Strengths of cohort studies include

Good for rare exposures, multiple outcomes, and allow a direct measurement of the incidence of disease in exposed and unexposed groups

Relative Risk is equal to 1 (RR = 1) or Odds Ratio is equal to 1 (OR = 1)

Incidence in the exposed and the unexposed is the same and the null hypothesis is true.

Retrospective cohort

Investigates rare exposures in a group of subjects to determine probable causes of a disease. Researchers may use health and other official records to retrieve data from prior years or decades

Secular time trends

Long term changes in health-related states or events refer to gradual changes in freq. of a disease over long time periods prevailing direction of disease occurrence (inc, dec, flat) - Helps evaluate programs or make policy decisions

200 babies were followed from birth to age five to determine if those whose mothers smoked during pregnancy were more likely to have respiratory infections in the first five years of life than those whose mothers did not smoke during pregnancy. The findings supported the investigators' assumption that smoking during pregnancy increases the frequency of respiratory infections in young children.

Prospectie cohort

Relative Risk is greater than 1 (RR > 1)

There is a larger incidence of disease (outcome) in the exposed than in the unexposed. Exposure appears to increase the probability of developing the disease (outcome). It shows a positive relationship between exposure and outcome.

Odds Ratio is less than 1 (OR < 1)

There is less incidence of disease (outcome) in cases than in controls. Indicates the exposure under study is a possible protective factor in mitigating the disease (outcome). When expressed mathematically, is always converted to a percentage.

Relative Risk is less than 1 (RR < 1)

There is less incidence of disease (outcome) in the exposed than in the unexposed. Exposure seems to decrease the probability of developing the disease (outcome). It shows a negative or inverse relationship between exposure and outcome. When expressed mathematically, is always converted to a percentage.

Odds Ratio is greater than 1 (OR > 1)

There is more incidence of disease (outcome) in cases than in controls. Indicates the exposure under study is a probable risk factor for the disease (outcome).

Ecologic

Used to assess the association between exposure and disease rates among different populations during the same time period.

Web of causation

Webs are graphic, pictorial, or paradigm representations of complex sets of events or conditions caused by an array of activities connected to a common core or common experience or event.

Screening

application of a test to persons who are asymptomatic in order to classify them as to their disease status -identify disease earlier to reduce severity of disease experience and to delay and/or reduce mortality from that disease -ex: PKU test in newborns, Pap smear, blood pressure tests, mammograms

analytical studies

evaluate one or more predetermined hypotheses about associations between exposure and outcome -what OR and RR are used for -three types: -case-control -cohort -clinical trial -cohort and clinical trial use RR

In an attempt to study the effect of vitamin C supplementation on the prevention of the common cold, researchers randomly assigned volunteers to take a prescribed amount of vitamin C or to take a placebo, and then followed up to see if the exposed group developed fewer colds than the unexposed group.

experimental

Epidemiological triangle

interrelatedness of 4 epidemiological factors often contributed to an outbreak of a disease: (1) the role of the host, (2) an agent or disease-causing organism, (3) the environmental circumstances needed for a disease to thrive, survive, and spread, and (4) time-related issues

A total of 825 insulation workers employed between 1941 and 1944 were identified from the personnel records of three large insulation manufacturing plants in the southeastern U.S. in 1975. During the period 1941-1975, 26 deaths from lung cancer were discovered among the workers. Only six lung cancer deaths, however, were reported among a comparable group of 700 coworkers who did not work with insulation during the same time period. The investigators had postulated that exposure to the insulation material increases the risk of lung cancer.

retrospective cohort