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Statistics, ethics and informed consent in anaesthesia

To read research in anaesthesia you need sensitivity, specificity, predictive values and NNT, and to understand which study answers which question; and to anaesthetise you need the informed consent of a competent patient, who receives information about risks and alternatives and may also refuse.

לקריאה בעברית

Why it matters in the exam

The exam asks about calculating sensitivity, specificity and predictive values from a table, the effect of prevalence on predictive value, NNT, type one and type two error and power, p and the confidence interval, types of study (controlled trial, cohort, case–control) and the measure suited to each, bias, and informed consent, capacity, emergency treatment, refusal of blood transfusion and a do-not-resuscitate order during surgery.

Sensitivity is the percentage of sick people the test detects (true positives divided by all the sick), and specificity is the percentage of healthy people the test rules out. The positive predictive value is the chance that a positive is truly sick, and it rises when the disease is more common; sensitivity and specificity do not depend on prevalence. NNT is 1 divided by the absolute risk reduction. A type one error (alpha, usually 0.05) is finding a difference that does not exist, and a type two error (beta) is missing a real difference; power is 1 minus beta, usually set at 80%. A 95% confidence interval that crosses 1 for an odds ratio or relative risk means the difference is not significant. A randomised controlled trial is best for comparing treatments, a cohort suits measuring relative risk, and a case–control study suits rare diseases and measures an odds ratio. Important biases are selection bias, confounding and lack of blinding.

The four principles of ethics are respect for autonomy, beneficence, non-maleficence and justice. Informed consent requires information about the nature of the treatment, its common and serious risks and the alternatives, capacity to understand and decide, and free will. The Israel Patient's Rights Law from 1996 requires informed consent for every medical treatment, and allows treatment without consent in an emergency of severe and immediate danger when consent cannot be obtained; in limited circumstances an ethics committee may approve treatment of a refusing patient. A competent adult may refuse blood transfusion, even if the refusal endangers life, and it is important to document in advance which products and methods are accepted. A do-not-resuscitate order is not cancelled automatically in surgery — it is discussed again with the patient before anaesthesia. When an error occurs, it is disclosed openly to the patient.

Key points

• Sensitivity and specificity are fixed; predictive values depend on prevalence.
• NNT = 1 divided by the absolute risk reduction.
• Alpha 0.05, power 80%, a confidence interval crossing 1 — not significant.
• Informed consent: information, capacity, free will.
• Emergency: treatment without consent; a competent adult may refuse.

Summary table

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Sources

• Israel Patient's Rights Law, 1996 — Informed consent and emergency treatment
• Beauchamp and Childress, Principles of Biomedical Ethics, 8th edition (2019) — The four principles
• Gordis Epidemiology, 6th edition (2019) — Diagnostic tests, study designs and bias

Sources are given for further reading; the text is written afresh and not copied from them.

Reviewed by the Examqo AI Professor · 2026-11-02. The text may contain errors; when in doubt, check the source.