Teaching tool · disease screening ethics

Trade-offs and the ethics of screening

Screening tests are seldom perfectly accurate. When they are accurate, they correctly warn individuals that they are or are not at risk for developing a disease. However, these early warnings and reassurances have to be traded off against cases in which screening tests incorrectly tell individuals that they do or do not have risk factors for or an early stage of a disease. Below, adjust the population and test parameters to see the impact on the costs and benefits associated with screening programs.

Scenario

Input population and test parameters

Total population screened

Base rate (true disease prevalence)0.00%

Sensitivity (true positive rate)0.0%

Specificity (true negative rate)0.0%

Results

True positive

—

Correctly told they may have the disease.

True negative

—

Correctly told they don’t have the disease.

False positive

—

Incorrectly told they may have the disease.

False negative

—

Incorrectly told they don’t have the disease.

Positive predictive value

—

Of people told they have the disease, the share who actually do.

Negative predictive value

—

Of people told they don’t have the disease, the share who actually don’t.

All screening outcomes

Screening outcomes without true negatives

Out of every 1,000 people screened

Squares are grouped by outcome, not randomly placed, so block sizes are easy to compare.

Quantifying costs and benefits

Trading off costs and benefits in the abstract can be difficult, so we often quantify them in terms of dollars. Input the monetary values for each outcome in this section. If it is difficult for you to come up with a dollar value, think in terms of ‘how much might I pay to gain a positive outcome (such as early treatment in the case of a true positive) or avoid a negative one (such as worry and unnecessary treatment in the case of a false positive).’

Include cost & benefit analysis

Cost per test

Benefit of a true positive

e.g., value of early treatment and disease averted.

Benefit of a true negative

e.g., reassurance, avoided unnecessary workup.

Cost of a false positive

Unnecessary anxiety, pain, risk and cost of further work-up and treatment.

Cost of a false negative

Treatment of more advanced disease, later found.

Cost of a true positive

Treatment costs, pain & suffering even when the diagnosis was correct.

Total cost of testing$0

Total cost of errors & treatment$0

Total benefits$0

Bottom line