• Pain

  For example, if a person would prefer 9 yr of health to 10 yr of chronic pain (but would prefer the 10 yr of pain to only 8 yr of life), then each year of life with pain is credited with 9/10 = 0.9 QALY. [merckmanuals.com]

  For example, if a person would prefer 9 years of health to 10 years of chronic pain (but would prefer the 10 years of pain to only 8 years of life), then each year of life with that particular pain is credited with 9/10 = 0.9 QALY. [msdmanuals.com]

In more complex analysis, death and disability are often evaluated in combination as the quality-adjusted life year (QALY); treatment that results in an additional year of life at 100% of normal functioning is credited with 1 QALY; treatment that results [merckmanuals.com]

Thus, if a drug causes a 3% net decrease in mortality, 1/0.03 = 33.3 patients need to be treated to prevent 1 death. The number needed to harm is similar. [msdmanuals.com]