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Doctoring Theory

Epidemiology the study of distribution and determinants of health-related states in specified populations and the application of this study to control health problems
Distribution Different criteria of people (age, sex, ethnicity, socioeconomic status, etc.)
Determinants risk factors and preventative factors (modifiable and non-modifiable)
Incidence Is a measure of disease frequency.a measure of the occurrence of new disease or change in state (the best outcome to study for epidemiology) – Deals a lot with exposure and risk of developing the disease
How is cumulative incidence expressed? as a percentage (# with disease / # at risk for the disease)
How is Incidence rate expressed? # of new cases/person-time
Prevalence a measure of disease frequency. It is the measurement of existing disease in a particular time period
How is prevalence expressed? (#with the disease) / total population. Sometimes shown as a percentage – don’t confuse with cumulative incidence! Usually used for chronic diseases (The number of people living with ______ disease)
Rate ratio the ratio between incidence rates of exposed vs. non-exposed.
What is the null value for rates ratio or odds ratio? Its null value is 1. A value < 1 suggests that those that are exposed are at a lower risk for disease than the non-exposed. A value > 1 suggests that those exposed are at a greater risk for disease than those not exposed.
Epidemic when there is a higher rate of disease than would be expected based on previous data. It is graphed as time vs. # of cases. Normally, the graph is flat, but during an epidemic, there is a large upward spike.
What is the difference between experimental and observational studies? in an experimental study, the investigator assigns the exposure to individuals. In an observational study, the exposure status is not determined by the investigator and thus can only be “observed.”
What are the defining characteristics of a case-control study? a case-control study is where individuals with the disease (cases) and individuals without the disease (controls) are picked and exposure is determined.
What are the advantages of a case control study? Efficiency, less-expensive, can study rare diseases, can study multiple exposures, can use existing records.
What are the disadvantages of a case control study? More potential for bias (disease has already occurred) in case selection and in how information on exposure is collected, more potential for confounding, records may be incomplete
Identify the defining characteristic of a cohort study Subjects are chosen/classified on the basis of exposure and are followed/traced to determine the outcome.
(4)retrospective Cohort study advantages can study rare exposures, can study multiple outcomes, can calculate incidence rate, may be less expensive if data is readily available
(5)Retrospective Cohort study Disadvantages Need a large sample, risk of loss of follow up data being present, poor information on exposure, more susceptible to bias, may be more expensive if data gathering needed
(5)Prospective cohort study advantages can study rare exposures, can study multiple outcomes, good information on exposure, can calculate incidence rates, bias less likely
(3)Prospective cohort study disadvantages requires a large sample, risk of loss of follow up, potential for uncontrolled confounding.
Identify the defining characteristics of cross-sectional studies subjects are enrolled in the study regardless or exposure/disease status. Exposure and disease are then measured simultaneously
Identify the defining characteristics of ecological studies correlation between exposure and health outcome at a population/geographic level. Used for hypothesis generation ONLY! No information on individuals – groups only. Susceptible to bias and confounding
Identify the defining characteristics of an experimental study (clinical trial) Subjects are assigned treatment/exposure by the investigator. Investigators then follow the subjects forward in calendar time until the disease/outcome occurs or the study ends.
(3)Advantages of an experimental study/clinical trial low bias and confounding because it is usually double blinded. You can study multiple outcomes for a single exposure better data quality.
(3)Disadvantages of an experimental study/clinical trial ethical risk more time and money than most may not be generalizable
Identify the defining characteristic of a meta-analysis systematic search of the lit for relevant studies meeting criteria for methodology & validity; results are combined and statistics applied for hypothesis testing & generating measure of outcome, p-values and/or confidence intervals
(2)Advantages of meta-analysis inexpensive, allows researcher to examine compare multiple studies and synthesize research in a meaningful way
(3) Disadvantages of meta-analysis Relies on existing data Bias Variability of the data
Define a review A review does not involve statistical techniques, it is just the author’s (skilled) opinion
Define a Confidence interval Used for significance testing. The numerical estimate of the measure of interest is ALWAYS within its confidence interval which is defined by a lower confidence limit and an upper confidence limit.
Define a 95% Confidence interval we have 95% confidence that the true value of the measure of interest lies within the CI.
alpha error a false positive, occurs when a statistical test rejects a true null hypothesis. e.g. if a null hypothesis states a patient is healthy, and the patient is indeed healthy, but the test rejects this hypothesis, falsely suggesting that the patient is sick.
beta error a false(-), occurs when the test fails to reject a false null hypothesis. e.g. if a null hypothesis states a patient is healthy, and the patient is in fact sick, but the test fails to reject the hypothesis, falsely suggesting that the patient is healthy.
Power is the probability that the null hypothesis will be rejected when it is in fact false; to increase study power, increase α
What is a p value? an attempt to answer the questions: what is the probability that I would get this result if the only explanation were chance?
What does it mean if p < .05 (α) ? the difference is real and not just due to chance reject the null hypothesis
What does it mean if p > .05? the difference is due to chance; DO NOT reject the null
Mean sum of measurements / # of observations; average
Median level below which 50% of the observations lie (or above which 50% of the observations lie)
Mode the most frequently occurring observation
When is it most appropriate to use the mean? for summarizing data that is close to a normal distribution (more affected by outlying data points).
When is it most appropriate to use the median? skewed data
Describe and recognize the four measures of variability Standard deviation Variance Percentiles (corresponds to median Range (corresponds to mode
List the three characteristics of a normal or Gaussian distribution or curve Symmetrical about its mean Mean = median = mode Bell-shaped
List the (3) conditions necessary to justify, and the requirements for, a screening program The disease is an important cause of mortality and/or morbidity. A proven and acceptable test exists to detect individuals at an early modifiable stage. There is safe and effective treatment available to treat the disease and its consequences
Sensitivity TP/(TP+FN) = among persons with disease, the percent that have a positive test
Specificity TN/(TN+FP) = among persons without disease, the percent that have a negative test
Predictive Value Positive TP/(TP+FP) = among persons with a positive test, the percent who have disease
Predictive value negative TN/(TN+FN) = among persons with a negative test, the percent who
Bias any trend in the collection, analysis, interpretation, publication or review of data that can lead to conclusions that are systematically different from the truth
Selection bias non-comparable criteria are used to select entrants into two groups of the study – most common when both exposure and disease have already occurred at the time the study begins
Information bias (observation bias) information is collected from the study groups in a non-comparable manner – ex
cohort v. case control studies cohort has 1 cohort & 2 exposures ( all have CVD, some take drug A, some don't) then evaluate; case control has 2 cohorts & 1 exposure (those with CVD, those without) all take Drug A then evaluate
What is the relationship between prevalence and incidence? P= I x duration
Created by: denpasar