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Questions and Answers
What are the two fundamental distinctions required in causal research in epidemiology?
What are the two fundamental distinctions required in causal research in epidemiology?
- Between people with and without exposure to the risk factor, and between men and women
- Between people who smoke and people who do not smoke, and between people who have hypertension and people who do not have hypertension
- Between people with and without the disease, and between high and low risk factors
- Between people who have and people who do not have exposure to the risk factor, and between people who have and people who do not have the disease (correct)
What is a complication in analyzing the relationship between exposure to a risk factor and the development of a disease?
What is a complication in analyzing the relationship between exposure to a risk factor and the development of a disease?
- The need to analyze multiple independent variables
- The need to measure the strength and duration of exposure to the risk factor
- The difficulty in determining the time of onset of exposure
- All of the above (correct)
What is an example of how age and gender interact in relation to hypertension?
What is an example of how age and gender interact in relation to hypertension?
- Men are more likely to be hypertensive after age 50, and women are more likely to be hypertensive before age 50
- There is no interaction between age and gender in relation to hypertension
- Men are more likely to be hypertensive before age 50, and women are more likely to be hypertensive after age 50 (correct)
- Women are more likely to be hypertensive at any age
What is the purpose of measuring exposure to cigarettes in terms of pack-years?
What is the purpose of measuring exposure to cigarettes in terms of pack-years?
What is a limitation of much epidemiologic research?
What is a limitation of much epidemiologic research?
What is a challenge in measuring the exposure to risk factors such as sedentary lifestyle and excess intake of dietary sodium?
What is a challenge in measuring the exposure to risk factors such as sedentary lifestyle and excess intake of dietary sodium?
What is a common way to present epidemiologic data?
What is a common way to present epidemiologic data?
Why do investigators study strength and duration of exposure to risk factors?
Why do investigators study strength and duration of exposure to risk factors?
What is the primary approach used in causal research to measure differences?
What is the primary approach used in causal research to measure differences?
In case-control studies, what is the focus of comparison?
In case-control studies, what is the focus of comparison?
What type of study allows investigators to obtain only a relative measure of risk?
What type of study allows investigators to obtain only a relative measure of risk?
What is the term for the difference in risk between the exposed and unexposed groups?
What is the term for the difference in risk between the exposed and unexposed groups?
What does an absolute risk difference of 0 indicate?
What does an absolute risk difference of 0 indicate?
What is the formula for calculating the attributable risk (AR)?
What is the formula for calculating the attributable risk (AR)?
What is the purpose of conducting significance testing in causal research?
What is the purpose of conducting significance testing in causal research?
What does a statistically significant difference but not clinically important result indicate?
What does a statistically significant difference but not clinically important result indicate?
What is the term for the rate of disease in population-based reporting systems?
What is the term for the rate of disease in population-based reporting systems?
What is the purpose of examining both absolute and relative risks in causal research?
What is the purpose of examining both absolute and relative risks in causal research?
What is the formula for calculating the relative risk (RR)?
What is the formula for calculating the relative risk (RR)?
What is the odds ratio (OR) in terms of the symbols used in Table 6-1?
What is the odds ratio (OR) in terms of the symbols used in Table 6-1?
Why is the odds ratio not a good estimate of the risk ratio if the risk of the disease is relatively large?
Why is the odds ratio not a good estimate of the risk ratio if the risk of the disease is relatively large?
What is the term for the ratio of the risk in the exposed group to the risk in the unexposed group?
What is the term for the ratio of the risk in the exposed group to the risk in the unexposed group?
What is the difference between the risk and the odds of a disease?
What is the difference between the risk and the odds of a disease?
What is the purpose of considering the number of people to whom the relative risk applies?
What is the purpose of considering the number of people to whom the relative risk applies?
Why is the odds ratio used in case-control studies?
Why is the odds ratio used in case-control studies?
What is the result of a relative risk calculation if the risk for the disease in the exposed group is 191/100,000 and the risk for the disease in the unexposed group is 8.7/100,000?
What is the result of a relative risk calculation if the risk for the disease in the exposed group is 191/100,000 and the risk for the disease in the unexposed group is 8.7/100,000?
What is the attributable risk in terms of absolute risk?
What is the attributable risk in terms of absolute risk?
What is the primary purpose of collecting and analyzing data in clinical medicine?
What is the primary purpose of collecting and analyzing data in clinical medicine?
What is the term used to describe mistakes in the diagnosis and treatment of patients in clinical medicine?
What is the term used to describe mistakes in the diagnosis and treatment of patients in clinical medicine?
What is the primary goal of data collection in clinical medicine?
What is the primary goal of data collection in clinical medicine?
What is accuracy in the context of data collection?
What is accuracy in the context of data collection?
What is the difference between accuracy and precision?
What is the difference between accuracy and precision?
What is the limitation of medical histories, physical examinations, laboratory values, and imaging reports?
What is the limitation of medical histories, physical examinations, laboratory values, and imaging reports?
Why is it important to minimize errors in data in clinical medicine?
Why is it important to minimize errors in data in clinical medicine?
What is the primary purpose of evaluating a diagnostic or screening test in two groups of individuals?
What is the primary purpose of evaluating a diagnostic or screening test in two groups of individuals?
What is a false-negative result in a diagnostic test?
What is a false-negative result in a diagnostic test?
What was the issue with the tuberculin skin test in the southeastern United States?
What was the issue with the tuberculin skin test in the southeastern United States?
What is a type I error in science?
What is a type I error in science?
Why may tests for infectious diseases be inaccurate?
Why may tests for infectious diseases be inaccurate?
What is the purpose of evaluating a diagnostic or screening test in a population with characteristics similar to those in whom the test would be used?
What is the purpose of evaluating a diagnostic or screening test in a population with characteristics similar to those in whom the test would be used?
What is anergy?
What is anergy?
What was changed to improve the tuberculin skin test?
What was changed to improve the tuberculin skin test?
Why may tests be less accurate in elderly individuals?
Why may tests be less accurate in elderly individuals?
What is the main difference between random error and measurement bias?
What is the main difference between random error and measurement bias?
What is the result when there are only random errors in data?
What is the result when there are only random errors in data?
What is the importance of accuracy and precision in data collection?
What is the importance of accuracy and precision in data collection?
What is the term for the difference in measurements or interpretations obtained by the same clinician when examining the same data multiple times?
What is the term for the difference in measurements or interpretations obtained by the same clinician when examining the same data multiple times?
What is the goal of data collection in terms of intraobserver and interobserver variability?
What is the goal of data collection in terms of intraobserver and interobserver variability?
What is the effect of random errors on data?
What is the effect of random errors on data?
What is the term for the error that results from measuring the heights of patients with their shoes on?
What is the term for the error that results from measuring the heights of patients with their shoes on?
What is the effect of measurement bias on data?
What is the effect of measurement bias on data?
What is the purpose of statistical analysis in relation to bias?
What is the purpose of statistical analysis in relation to bias?
What is the result of having data that is precise but not accurate?
What is the result of having data that is precise but not accurate?
What is the term for the rate at which a test fails to detect disease in diseased participants?
What is the term for the rate at which a test fails to detect disease in diseased participants?
What is the purpose of reporting sensitivity and specificity of a diagnostic test?
What is the purpose of reporting sensitivity and specificity of a diagnostic test?
What is the formula to calculate sensitivity?
What is the formula to calculate sensitivity?
What is the tradeoff between sensitivity and specificity in a diagnostic test?
What is the tradeoff between sensitivity and specificity in a diagnostic test?
What is the formula to calculate specificity?
What is the formula to calculate specificity?
What is an example of a false-positive result in a diagnostic test?
What is an example of a false-positive result in a diagnostic test?
What is the purpose of publishing a range of 'normal' values for substances measured in a laboratory?
What is the purpose of publishing a range of 'normal' values for substances measured in a laboratory?
What is the purpose of creating a 2 × 2 table to evaluate the performance of a diagnostic test?
What is the purpose of creating a 2 × 2 table to evaluate the performance of a diagnostic test?
What is the result of setting the cutoff point for a diagnostic test too low?
What is the result of setting the cutoff point for a diagnostic test too low?
Why is it important to determine the sensitivity, specificity, and predictive values of a diagnostic test?
Why is it important to determine the sensitivity, specificity, and predictive values of a diagnostic test?
What is the consequence of the overlap between the distribution of test values in diseased and nondiseased persons?
What is the consequence of the overlap between the distribution of test values in diseased and nondiseased persons?
What is an example of a false-negative result in a diagnostic test?
What is an example of a false-negative result in a diagnostic test?
Why is it important to consider both the sensitivity and specificity of a diagnostic test?
Why is it important to consider both the sensitivity and specificity of a diagnostic test?
What is the purpose of serial calcium tests in patients with suspected hyperparathyroidism?
What is the purpose of serial calcium tests in patients with suspected hyperparathyroidism?
What is the likelihood ratio positive (LR+) a measure of?
What is the likelihood ratio positive (LR+) a measure of?
What does a higher likelihood ratio positive (LR+) indicate?
What does a higher likelihood ratio positive (LR+) indicate?
What is the likelihood ratio negative (LR-) a measure of?
What is the likelihood ratio negative (LR-) a measure of?
What does a smaller likelihood ratio negative (LR-) indicate?
What does a smaller likelihood ratio negative (LR-) indicate?
What is the formula for calculating the likelihood ratio positive (LR+)?
What is the formula for calculating the likelihood ratio positive (LR+)?
What is the purpose of calculating the ratio of LR+ to LR-?
What is the purpose of calculating the ratio of LR+ to LR-?
What is the primary purpose of calculating the positive predictive value (PPV) and negative predictive value (NPV)?
What is the primary purpose of calculating the positive predictive value (PPV) and negative predictive value (NPV)?
What is the main reason why predictive values are difficult to interpret?
What is the main reason why predictive values are difficult to interpret?
What is the term for a test that elicits a reaction synonymous with having the disease?
What is the term for a test that elicits a reaction synonymous with having the disease?
What is the primary advantage of likelihood ratios compared to predictive values?
What is the primary advantage of likelihood ratios compared to predictive values?
Why is it important to consider the prevalence of a disease when interpreting the results of a screening test?
Why is it important to consider the prevalence of a disease when interpreting the results of a screening test?
What is the primary purpose of a screening test?
What is the primary purpose of a screening test?
What is the main difference between a screening test and a confirmatory test?
What is the main difference between a screening test and a confirmatory test?
What is the result of a predictive value calculation if there are no false-positive or false-negative errors?
What is the result of a predictive value calculation if there are no false-positive or false-negative errors?
What is the primary purpose of calculating the sensitivity and specificity of a test?
What is the primary purpose of calculating the sensitivity and specificity of a test?
Why is it important to follow up with additional testing in individuals who have a positive screening test result?
Why is it important to follow up with additional testing in individuals who have a positive screening test result?
Why is the point closest to the upper left corner considered the best cutoff point?
Why is the point closest to the upper left corner considered the best cutoff point?
What is the purpose of analyzing the data for different cutoff points?
What is the purpose of analyzing the data for different cutoff points?
What happens when the cutoff point is very low, such as 120 mm Hg?
What happens when the cutoff point is very low, such as 120 mm Hg?
What is the primary purpose of a screening test in a diagnosis?
What is the primary purpose of a screening test in a diagnosis?
What is the term for the ratio of the risk in the exposed group to the risk in the unexposed group?
What is the term for the ratio of the risk in the exposed group to the risk in the unexposed group?
What is the difference between sensitivity and specificity in medical tests?
What is the difference between sensitivity and specificity in medical tests?
What is the primary goal of a confirmatory test in a diagnosis?
What is the primary goal of a confirmatory test in a diagnosis?
What is the term for the proportion of true cases of a disease that are detected by a test?
What is the term for the proportion of true cases of a disease that are detected by a test?
What is the purpose of using the mnemonic 'spin' in medical testing?
What is the purpose of using the mnemonic 'spin' in medical testing?
What is the difference between a proportion and an odds?
What is the difference between a proportion and an odds?
What is the primary goal of using tests with high sensitivity in medical diagnosis?
What is the primary goal of using tests with high sensitivity in medical diagnosis?
What is the primary purpose of a receiver operating characteristic (ROC) curve?
What is the primary purpose of a receiver operating characteristic (ROC) curve?
What is the formula for converting odds to probability?
What is the formula for converting odds to probability?
What is the definition of sensitivity in a diagnostic test?
What is the definition of sensitivity in a diagnostic test?
What is the purpose of setting a cutoff point in a diagnostic test?
What is the purpose of setting a cutoff point in a diagnostic test?
What is the difference between a proportion and an odds?
What is the difference between a proportion and an odds?
What is the result of setting a cutoff point at 0 mm Hg in a blood pressure screening program?
What is the result of setting a cutoff point at 0 mm Hg in a blood pressure screening program?
What is the limitation of using a very high cutoff point in a diagnostic test?
What is the limitation of using a very high cutoff point in a diagnostic test?
What is the relationship between the odds and the probability of an outcome?
What is the relationship between the odds and the probability of an outcome?
Study Notes
Causal Research in Epidemiology
- Causal research in epidemiology requires two fundamental distinctions:
- distinction between people who have and people who do not have exposure to the risk factor (or protective factor) under study (independent variable)
- distinction between people who have and people who do not have the disease (or other outcome) under study (dependent variable)
Complications of Epidemiologic Research
- Measurements of exposure and outcome are subject to random errors and biases
- Analysis may be complicated by the need to analyze several independent (possibly causal) variables at the same time, including interactions
- Measuring different degrees of strength of exposure to the risk factor, duration of exposure, or both, may be necessary
- Determining the time of onset of exposure may be difficult for risk factors such as sedentary lifestyle and excess intake of dietary sodium
- Measuring different levels of disease severity is necessary as exposure and outcome may vary across a range of values
Definition of Study Groups
- Causal research depends on the measurement of differences in cohort studies and case-control studies
- In cohort studies, the difference is between the frequency of disease in persons exposed to a risk factor and the frequency of disease in persons not exposed to the same risk factor
- In case-control studies, the difference is between the frequency of the risk factor in case participants (persons with the disease) and the frequency of the risk factor in control participants (persons without the disease)
Comparison of Risks in Different Study Groups
- Differences in risk can be measured in absolute terms or in relative terms
- Absolute differences in risks or rates can be expressed as a risk difference or as a rate difference
- Relative differences in risks or rates can be expressed as a relative risk (RR) or an odds ratio (OR)
Absolute Differences in Risk
- The risk difference is the risk in the exposed group minus the risk in the unexposed group
- The rate difference is the rate in the exposed group minus the rate in the unexposed group
- The risk difference is also known as the attributable risk because it is an estimate of the amount of risk that can be attributed to, or is caused by, the risk factor
Relative Differences in Risk
- The relative risk (RR) can be expressed in terms of a risk ratio or an odds ratio
- The risk ratio is the ratio of the risk in the exposed group to the risk in the unexposed group
- The odds ratio (OR) is the ratio of the odds of exposure in the diseased group to the odds of exposure in the nondiseased group
Data Collection and Analysis
- Clinical medicine requires constant collection, evaluation, analysis, and use of quantitative and qualitative data.
- Data are used for diagnosis, prognosis, and choosing and evaluating treatments.
- Errors in data can occur and are difficult to eliminate, and can be categorized into differential errors (bias) and nondifferential errors (random errors).
Promoting Accuracy and Precision
- Two distinct goals of data collection are accuracy and precision.
- Accuracy refers to the ability of a measurement to be correct on average, while precision refers to the ability of a measurement to give the same result or a similar result with repeated measurements.
- Both accuracy and precision are essential for data collection, as either one alone is not sufficient.
Reducing Errors
- There are two types of errors to avoid in data collection: differential errors (bias) and nondifferential errors (random errors).
- Differential errors result from systematic or consistent errors that tend to be inaccurate in a particular direction.
- Nondifferential errors result from random errors that can produce both high and low values.
Intraobserver and Interobserver Variability
- Intraobserver variability refers to the differences in measurements or interpretations obtained by the same clinician when measuring or interpreting the same data multiple times.
- Interobserver variability refers to the differences in measurements or interpretations obtained by different clinicians when measuring or interpreting the same data.
- Reducing intraobserver and interobserver variability is essential to ensure accurate and reliable data.
Studying the Accuracy and Usefulness of Screening and Diagnostic Tests
- The accuracy and usefulness of screening and diagnostic tests can be evaluated by assessing their performance in two groups of individuals: those with the disease and those without the disease.
- Factors that influence the accuracy and usefulness of tests include the stage of the disease, the spectrum of disease in the study population, and the characteristics of the population being tested.
False-Positive and False-Negative Results
- False-positive results occur when a test result is positive in a person without the disease.
- False-negative results occur when a test result is negative in a person with the disease.
- False-positive and false-negative results can be influenced by the stage of the disease, the spectrum of disease in the study population, and the characteristics of the population being tested.
Sensitivity and Specificity
- Sensitivity refers to the ability of a test to detect a disease when present, and is calculated as the proportion of true-positive results among all diseased individuals.
- Specificity refers to the ability of a test to indicate nondisease when no disease is present, and is calculated as the proportion of true-negative results among all nondiseased individuals.
- Both sensitivity and specificity are essential measures of a test's performance.
Predictive Values
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Predictive values are used to answer two important clinical questions: what is the probability that a person has the disease if the test result is positive, and what is the probability that a person does not have the disease if the test result is negative.
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Positive predictive value (PPV) is the proportion of true-positive results among all positive test results.
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Negative predictive value (NPV) is the proportion of true-negative results among all negative test results.
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Predictive values are influenced by the prevalence of the condition being tested, and can be difficult to interpret in the presence of false-positive or false-negative results.### Screening Tests and Confirmatory Tests
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When clinicians test for rare conditions, most positive test results are likely to be falsely positive
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Additional testing is necessary to determine if the disease is present in individuals with positive results
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Screening tests are still worthwhile for conditions with low prevalence, as the number of individuals requiring follow-up diagnostic tests may be small
Principles of Screening Tests and Confirmatory Tests
- One test does not make a diagnosis, unless it is a pathognomonic test (a "gold standard")
- Box 7-1 summarizes key principles concerning screening tests and confirmatory tests
Likelihood Ratios, Odds Ratios, and Cutoff Points
- Likelihood ratios are not influenced by the prevalence of the disease
- Likelihood ratio positive (LR+) is the ratio of sensitivity to false-positive error rate
- LR+ = [a/(a + c)] ÷ [b/(b + d)]
- A higher LR+ indicates a better test, with a ratio much larger than 1
- Sensitivity and false-positive error rate are independent of disease prevalence, and their ratio is also independent
- Likelihood ratio negative (LR-) is the ratio of false-negative error rate to specificity
- LR- = [c/(a + c)] ÷ [d/(b + d)]
- A smaller LR- indicates a better test, with a ratio closer to 0
- If LR+ is large and LR- is small, it is likely a good test
- Experts in test analysis sometimes calculate the ratio of LR+ to LR- to obtain a measure of separation between positive and negative tests
Characteristics of Tests Needed to “Rule Out” and “Rule In” a Diagnosis
- A clinician must order various tests to screen or “rule out” (discard) false hypotheses when a patient presents with complaints.
- These tests should be highly sensitive tests, which have a low false-negative error rate, to ensure that not many true cases of the disease are missed.
- After most of the hypothesized diagnoses have been eliminated, the clinician begins to consider tests to “rule in” (confirm) the true diagnosis.
- These tests should be highly specific tests, which have a small false-positive error rate, to ensure that not many patients are misdiagnosed as having a particular disease when in fact they have another disease.
Principles of Testing
- A screening test, used to rule out a diagnosis, should have a high degree of sensitivity.
- A confirmatory test, used to rule in a diagnosis, should have a high degree of specificity.
Concepts of Proportions and Odds
- A proportion is a ratio of the form a/(a + b), whereas an odds is a ratio of the form a/b.
- Odds can only describe a variable that is dichotomous (i.e., has only two possible outcomes).
- The odds of a particular outcome can be converted to the probability of that outcome, and vice versa, using the formula: Probability of outcome X = Odds of outcome X / (1 + Odds of outcome X).
Receiver Operating Characteristic (ROC) Curves
- ROC curves are used to decide on a good cutoff point for a clinical test that measures continuous variables.
- The curve plots the sensitivity of a test against the false-positive error rate for several possible cutoff points.
- The y-axis shows the sensitivity of a test, and the x-axis shows the false-positive error rate (1 - specificity).
- The ROC curve can be considered a graph of the Likelihood Ratio (LR+).
- The ideal ROC curve for a test would rise almost vertically from the lower left corner and move horizontally almost along the upper line, indicating a high sensitivity and a low false-positive error rate.
- The ROC curve for most clinical tests is somewhere between the ideal and the no benefit line, which represents a diagonal straight line from the lower left to the upper right corner.
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Description
This quiz covers the fundamental distinctions in causal research, including exposure to risk factors and presence of disease, and the challenges of measuring these variables.