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Zorluk: ZorDiagnostic and Screening Test Performance

A regional public health authority is implementing a targeted screening program for a newly identified strain of avian influenza in poultry workers. In this high-risk occupational cohort, the estimated prevalence of the infection is 30%. A rapid point-of-care serological test used in this cohort demonstrates a positive predictive value of 85% and a negative predictive value of 95%. Two months later, to alleviate public anxiety, policymakers mandate expanding the screening program to include all residents of the surrounding county, where the estimated prevalence of the infection is 2%. Assuming the sensitivity and specificity of the serological test are constant across both groups, which of the following is the most likely consequence of expanding this screening program to the general county population?

  1. The proportion of false-positive results among all positive tests will increase.Cevap
  2. B
    The proportion of false-negative results among all negative tests will increase.
  3. C
    The positive likelihood ratio of the serological test will decrease.
  4. D
    The area under the receiver operating characteristic curve will decrease.
  5. E
    The negative likelihood ratio of the serological test will increase.

Cevap

The proportion of false-positive results among all positive tests will increase.
Positive predictive value (PPV) is highly dependent on disease prevalence. When the test is applied to a population with a much lower prevalence (2% vs 30%), the PPV will significantly decrease. PPV is defined as the proportion of true positives among all positive results (TP / (TP + FP)). If the PPV decreases, the proportion of false positives among all positive tests—also known as the false discovery rate, calculated as (FP / (TP + FP)) or 1 - PPV—must necessarily increase. Consequently, in the low-prevalence general population, a greater percentage of individuals who test positive will not actually have the disease.

Adım Adım Çözüm

1
Identify the change in population parameters.
Disease prevalence drops from 30% in the occupational cohort to 2% in the general county population, while sensitivity and specificity remain constant.
To determine which statistical properties of the test will be affected by the intervention.
2
Evaluate the effect of decreased prevalence on predictive values.
Positive Predictive Value (PPV) will decrease, and Negative Predictive Value (NPV) will increase.
Prevalence directly impacts predictive values: lower prevalence yields fewer true positives relative to false positives in the tested population.
3
Analyze the answer choices based on the predictive value changes.
A decreased PPV (True Positives / All Positives) mathematically dictates an increase in the proportion of false positives among all positive tests (False Positives / All Positives).
To identify the correct conceptual description of the statistical change requested by the stem.

Anahtar Kavram

The effect of disease prevalence on Positive Predictive Value (PPV) and Negative Predictive Value (NPV), and the distinction between prevalence-dependent values (PPV, NPV) and intrinsic test properties (Sensitivity, Specificity, Likelihood Ratios).
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Konular

Diagnostic and Screening Test Performance

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