Relative Risk Calculator
The Relative Risk Calculator computes the ratio of event probabilities between exposed and unexposed groups in cohort studies. Determine relative risk (RR), absolute risk reduction (ARR), and number needed to treat (NNT) from your study data.
What is Relative Risk?
Relative risk (RR) compares the probability of an event in the exposed group to the probability in the unexposed group. An RR of 2.0 means exposed individuals are twice as likely to experience the outcome. An RR of 0.5 means exposure halves the risk (50% risk reduction).
Relative risk is the standard measure of association in cohort studies and randomized controlled trials. It's more intuitive than odds ratio because it directly represents probability ratios. RR = 1.0 means no difference between groups.
Формулы и Используемые Уравнения
В калькуляторе заложены 5 основных уравнений:
1 Relative Risk ▼
Risk in exposed = a/(a+b). Risk in unexposed = c/(c+d). RR is their ratio.
2 Absolute Risk Reduction ▼
If control risk = 20% and treatment risk = 12%: ARR = 20% - 12% = 8 percentage points.
3 Number Needed to Treat ▼
ARR of 8%: NNT = 1/0.08 = 12.5. You need to treat 13 patients to prevent 1 event.
Как Пользоваться Калькулятором
Чтобы использовать этот Калькулятор Отношений, выполните 3 простых шага:
Введите Данные
Введите известные числа в поля ввода. Оставьте одно поле пустым — калькулятор вычислит это неизвестное значение.
Выберите Режим
Выберите режим работы — Решение пропорций, Упрощение отношений или Масштабирование. В каждом режиме используются свои математические формулы.
Получите Результат
Нажмите кнопку Вычислить. На экране отобразится ответ с цветной шкалой отношения, круговой диаграммой и пошаговым решением.
Примеры Задач с Пошаговыми Решениями
Вот 3 практических примера расчетов с подробным математическим описанием действий:
Ввод 1 Drug trial: treated group vs placebo
Ввод 2 Smoking and heart disease (cohort study)
Ввод 3 Calculate NNT for a vaccine
Часто Задаваемые Вопросы
What does a relative risk of 1.0 mean? ▼
RR = 1.0 means the event is equally likely in both groups — no association between exposure and outcome. RR > 1 indicates increased risk; RR < 1 indicates decreased risk (protection).
How is relative risk different from odds ratio? ▼
RR uses probabilities (events/total), while OR uses odds (events/non-events). For rare outcomes (<10%), they're nearly equal. For common outcomes, OR overstates the association compared to RR.
What is a clinically significant relative risk? ▼
This depends on context. In cancer screening, RR = 0.80 (20% risk reduction) may be significant. In vaccine trials, RR = 0.05 (95% efficacy) is transformative. Always consider both RR and ARR.
Can relative risk be used in case-control studies? ▼
No. Case-control studies sample by outcome, not exposure, so you can't calculate true incidence rates. Use odds ratio instead. RR is only valid in cohort studies and RCTs where you follow groups over time.
What is the number needed to treat (NNT)? ▼
NNT is the inverse of absolute risk reduction. It tells you how many patients must receive treatment to prevent one adverse event. Lower NNT = more effective treatment. NNT of 10 means treat 10 patients to prevent 1 event.