Preventive Medicine: Epidemiology 6

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Questions and Answers

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?

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?

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?

To combine the strength and duration of exposure to cigarettes Signup and view all the answers

What is a limitation of much epidemiologic research?

It relies on the dichotomies of exposed/unexposed and diseased/nondiseased Signup and view all the answers

What is a challenge in measuring the exposure to risk factors such as sedentary lifestyle and excess intake of dietary sodium?

Determining the time of onset of exposure Signup and view all the answers

What is a common way to present epidemiologic data?

In a 2x2 table Signup and view all the answers

Why do investigators study strength and duration of exposure to risk factors?

To measure the exposure to the risk factor in different ways Signup and view all the answers

What is the primary approach used in causal research to measure differences?

Comparing the frequency of disease in exposed and unexposed groups Signup and view all the answers

In case-control studies, what is the focus of comparison?

The frequency of the risk factor in case and control participants Signup and view all the answers

What type of study allows investigators to obtain only a relative measure of risk?

Case-control studies Signup and view all the answers

What is the term for the difference in risk between the exposed and unexposed groups?

Risk difference Signup and view all the answers

What does an absolute risk difference of 0 indicate?

The exposure makes no difference to disease risk Signup and view all the answers

What is the formula for calculating the attributable risk (AR)?

AR = [a/(a+b)]−[c/(c+d)] Signup and view all the answers

What is the purpose of conducting significance testing in causal research?

To ensure that any observed difference is probably real and not caused by chance Signup and view all the answers

What does a statistically significant difference but not clinically important result indicate?

The difference is real but trivial Signup and view all the answers

What is the term for the rate of disease in population-based reporting systems?

Rate Signup and view all the answers

What is the purpose of examining both absolute and relative risks in causal research?

To provide different information about the risk factor Signup and view all the answers

What is the formula for calculating the relative risk (RR)?

RR = Risk(exposed) / Risk(unexposed) Signup and view all the answers

What is the odds ratio (OR) in terms of the symbols used in Table 6-1?

OR = (a/c)/(b/d) = ad/bc Signup and view all the answers

Why is the odds ratio not a good estimate of the risk ratio if the risk of the disease is relatively large?

Because the odds would be very different from the risk Signup and view all the answers

What is the term for the ratio of the risk in the exposed group to the risk in the unexposed group?

Relative risk Signup and view all the answers

What is the difference between the risk and the odds of a disease?

The risk is the probability of a disease, while the odds is the ratio of the probability of a disease to the probability of no disease Signup and view all the answers

What is the purpose of considering the number of people to whom the relative risk applies?

To determine the number of excess deaths or cases of disease Signup and view all the answers

Why is the odds ratio used in case-control studies?

Because it can be used to estimate the risk ratio when the risk of disease is low Signup and view all the answers

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?

RR = 22 Signup and view all the answers

What is the attributable risk in terms of absolute risk?

The difference between the risk in the exposed group and the risk in the unexposed group Signup and view all the answers

What is the primary purpose of collecting and analyzing data in clinical medicine?

To diagnose, prognose, and evaluate treatments Signup and view all the answers

What is the term used to describe mistakes in the diagnosis and treatment of patients in clinical medicine?

Error Signup and view all the answers

What is the primary goal of data collection in clinical medicine?

To promote accuracy and precision Signup and view all the answers

What is accuracy in the context of data collection?

The ability of a measurement to be correct on the average Signup and view all the answers

What is the difference between accuracy and precision?

Accuracy is related to bias, while precision is related to reproducibility Signup and view all the answers

What is the limitation of medical histories, physical examinations, laboratory values, and imaging reports?

They are imperfect due to human limitations Signup and view all the answers

Why is it important to minimize errors in data in clinical medicine?

To guide, rather than mislead, healthcare providers Signup and view all the answers

What is the primary purpose of evaluating a diagnostic or screening test in two groups of individuals?

To evaluate the test results in individuals with and without the disease Signup and view all the answers

What is a false-negative result in a diagnostic test?

A negative result in a patient with the disease Signup and view all the answers

What was the issue with the tuberculin skin test in the southeastern United States?

The test showed false-positive results due to exposure to atypical mycobacteria Signup and view all the answers

What is a type I error in science?

Saying something is true when it is false Signup and view all the answers

Why may tests for infectious diseases be inaccurate?

Because the test requires immunity to have developed Signup and view all the answers

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?

To evaluate the test's usefulness in the real world Signup and view all the answers

What is anergy?

An inadequate immune system response Signup and view all the answers

What was changed to improve the tuberculin skin test?

The standardization of the test was tightened Signup and view all the answers

Why may tests be less accurate in elderly individuals?

Because elderly individuals are more likely to have a weaker immune system Signup and view all the answers

What is the main difference between random error and measurement bias?

Random error is nondifferential, while measurement bias is differential. Signup and view all the answers

What is the result when there are only random errors in data?

The data produces a correct estimate of the average value if there are enough observations. Signup and view all the answers

What is the importance of accuracy and precision in data collection?

Both accuracy and precision are equally important and must be present for the data to be useful. Signup and view all the answers

What is the term for the difference in measurements or interpretations obtained by the same clinician when examining the same data multiple times?

Intraobserver variability. Signup and view all the answers

What is the goal of data collection in terms of intraobserver and interobserver variability?

To reduce the amount of variability. Signup and view all the answers

What is the effect of random errors on data?

It results in lack of precision but not accuracy. Signup and view all the answers

What is the term for the error that results from measuring the heights of patients with their shoes on?

Measurement bias. Signup and view all the answers

What is the effect of measurement bias on data?

It results in lack of accuracy but not precision. Signup and view all the answers

What is the purpose of statistical analysis in relation to bias?

To correct for bias if the amount of bias in each individual measurement is known. Signup and view all the answers

What is the result of having data that is precise but not accurate?

The data is misleading and may be dangerous. Signup and view all the answers

What is the term for the rate at which a test fails to detect disease in diseased participants?

False-negative error rate Signup and view all the answers

What is the purpose of reporting sensitivity and specificity of a diagnostic test?

To evaluate the test's accuracy Signup and view all the answers

What is the formula to calculate sensitivity?

a/(a + c) Signup and view all the answers

What is the tradeoff between sensitivity and specificity in a diagnostic test?

Between reliably finding a disease and avoiding false negatives Signup and view all the answers

What is the formula to calculate specificity?

d/(b + d) Signup and view all the answers

What is an example of a false-positive result in a diagnostic test?

A patient without hyperparathyroidism who has an elevated calcium level Signup and view all the answers

What is the purpose of publishing a range of 'normal' values for substances measured in a laboratory?

To provide a reference point for further diagnostic tests Signup and view all the answers

What is the purpose of creating a 2 × 2 table to evaluate the performance of a diagnostic test?

To calculate sensitivity and specificity Signup and view all the answers

What is the result of setting the cutoff point for a diagnostic test too low?

Wasting time and money on follow-up tests Signup and view all the answers

Why is it important to determine the sensitivity, specificity, and predictive values of a diagnostic test?

To choose the best cutoff point for the test Signup and view all the answers

What is the consequence of the overlap between the distribution of test values in diseased and nondiseased persons?

There is a risk of false-positive and false-negative results Signup and view all the answers

What is an example of a false-negative result in a diagnostic test?

A patient with hyperparathyroidism who has a normal calcium level Signup and view all the answers

Why is it important to consider both the sensitivity and specificity of a diagnostic test?

To understand the tradeoff between reliably finding a disease and avoiding false positives Signup and view all the answers

What is the purpose of serial calcium tests in patients with suspected hyperparathyroidism?

To confirm the diagnosis of hyperparathyroidism if the calcium level is elevated Signup and view all the answers

What is the likelihood ratio positive (LR+) a measure of?

The ratio of sensitivity to false-positive error rate Signup and view all the answers

What does a higher likelihood ratio positive (LR+) indicate?

A better test Signup and view all the answers

What is the likelihood ratio negative (LR-) a measure of?

The ratio of false-negative error rate to specificity Signup and view all the answers

What does a smaller likelihood ratio negative (LR-) indicate?

A better test Signup and view all the answers

What is the formula for calculating the likelihood ratio positive (LR+)?

[a/(a + c)] ÷ [b/(b + d)] Signup and view all the answers

What is the purpose of calculating the ratio of LR+ to LR-?

To obtain a measure of separation between the positive and the negative test Signup and view all the answers

What is the primary purpose of calculating the positive predictive value (PPV) and negative predictive value (NPV)?

To determine the probability of a disease given a positive or negative test result Signup and view all the answers

What is the main reason why predictive values are difficult to interpret?

Because they are influenced by the prevalence of the condition being tested Signup and view all the answers

What is the term for a test that elicits a reaction synonymous with having the disease?

Pathognomonic test Signup and view all the answers

What is the primary advantage of likelihood ratios compared to predictive values?

They are not influenced by the prevalence of the disease Signup and view all the answers

Why is it important to consider the prevalence of a disease when interpreting the results of a screening test?

Because it affects the predictive values of the test Signup and view all the answers

What is the primary purpose of a screening test?

To identify individuals who may have a disease and require further testing Signup and view all the answers

What is the main difference between a screening test and a confirmatory test?

A screening test is used to identify individuals who may have a disease, while a confirmatory test is used to confirm the presence of a disease Signup and view all the answers

What is the result of a predictive value calculation if there are no false-positive or false-negative errors?

The predictive value is 100% Signup and view all the answers

What is the primary purpose of calculating the sensitivity and specificity of a test?

To evaluate the accuracy of the test Signup and view all the answers

Why is it important to follow up with additional testing in individuals who have a positive screening test result?

To confirm the presence of the disease Signup and view all the answers

Why is the point closest to the upper left corner considered the best cutoff point?

It has a high sensitivity and a low false-positive error rate Signup and view all the answers

What is the purpose of analyzing the data for different cutoff points?

To determine the best cutoff point for diagnosis Signup and view all the answers

What happens when the cutoff point is very low, such as 120 mm Hg?

Sensitivity is high and false-positive error rate is low Signup and view all the answers

What is the primary purpose of a screening test in a diagnosis?

To rule out a diagnosis Signup and view all the answers

What is the term for the ratio of the risk in the exposed group to the risk in the unexposed group?

Relative risk Signup and view all the answers

What is the difference between sensitivity and specificity in medical tests?

Sensitivity measures true positives, while specificity measures true negatives Signup and view all the answers

What is the primary goal of a confirmatory test in a diagnosis?

To confirm a diagnosis Signup and view all the answers

What is the term for the proportion of true cases of a disease that are detected by a test?

Sensitivity Signup and view all the answers

What is the purpose of using the mnemonic 'spin' in medical testing?

To remember the importance of specificity in confirmatory tests Signup and view all the answers

What is the difference between a proportion and an odds?

A proportion is a/(a + b), while an odds is a/b Signup and view all the answers

What is the primary goal of using tests with high sensitivity in medical diagnosis?

To ensure that not many true cases of the disease are missed Signup and view all the answers

What is the primary purpose of a receiver operating characteristic (ROC) curve?

To evaluate the performance of a diagnostic test Signup and view all the answers

What is the formula for converting odds to probability?

Probability = Odds / (1 + Odds) Signup and view all the answers

What is the definition of sensitivity in a diagnostic test?

The proportion of true positives Signup and view all the answers

What is the purpose of setting a cutoff point in a diagnostic test?

To decide on the best point to distinguish between healthy and diseased individuals Signup and view all the answers

What is the difference between a proportion and an odds?

A proportion is a ratio of two numbers, while an odds is a ratio of a number to its complement Signup and view all the answers

What is the result of setting a cutoff point at 0 mm Hg in a blood pressure screening program?

All individuals are suspected to have hypertension Signup and view all the answers

What is the limitation of using a very high cutoff point in a diagnostic test?

There are many false-negative results Signup and view all the answers

What is the relationship between the odds and the probability of an outcome?

The odds is the probability divided by its complement Signup and view all the answers

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

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.
Positive predictive value (PPV) is the proportion of true-positive results among all positive test results.
Negative predictive value (NPV) is the proportion of true-negative results among all negative test results.
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
When clinicians test for rare conditions, most positive test results are likely to be falsely positive
Additional testing is necessary to determine if the disease is present in individuals with positive results
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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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.

Preventive Medicine: Epidemiology 6

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Questions and Answers

What are the two fundamental distinctions required in causal research in epidemiology?

What is a complication in analyzing the relationship between exposure to a risk factor and the development of a disease?

What is an example of how age and gender interact in relation to hypertension?

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 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?

Why do investigators study strength and duration of exposure to risk factors?

What is the primary approach used in causal research to measure differences?

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 is the term for the difference in risk between the exposed and unexposed groups?

What does an absolute risk difference of 0 indicate?

What is the formula for calculating the attributable risk (AR)?

What is the purpose of conducting significance testing in causal research?

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 purpose of examining both absolute and relative risks in causal research?

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?

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 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?

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 attributable risk in terms of absolute risk?

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 primary goal of data collection in clinical medicine?

What is accuracy in the context of data collection?

What is the difference between accuracy and precision?

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?

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 was the issue with the tuberculin skin test in the southeastern United States?

What is a type I error in science?

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 anergy?

What was changed to improve the tuberculin skin test?

Why may tests be less accurate in elderly individuals?

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 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 goal of data collection in terms of intraobserver and interobserver variability?

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 effect of measurement bias on data?

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 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 formula to calculate sensitivity?

What is the tradeoff between sensitivity and specificity in a diagnostic test?

What is the formula to calculate specificity?

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 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?

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 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?

What is the purpose of serial calcium tests in patients with suspected hyperparathyroidism?

What is the likelihood ratio positive (LR+) a measure of?

What does a higher likelihood ratio positive (LR+) indicate?

What is the likelihood ratio negative (LR-) a measure of?

What does a smaller likelihood ratio negative (LR-) indicate?

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 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 term for a test that elicits a reaction synonymous with having the disease?