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.
🕐 Recent Calculations
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.
Wzory i Zastosowane Równania
Kalkulator opiera się na 5 podstawowych równaniach:
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.
Jak Korzystać z Kalkulatora
Aby skorzystać z tego kalkulatora stosunku, wykonaj 3 proste kroki:
Wprowadź Dane
Wpisz znane wartości w pola wejściowe. Jedno pole pozostaw puste — jest to niewiadoma, którą obliczy kalkulator.
Wybierz Tryb
Wybierz tryb pracy — Rozwiązywanie proporcji, Upraszczanie lub Skalowanie. Każdy tryb stosuje inne równania.
Odbierz Wynik
Kliknij Oblicz. Ekran wyników wyświetla odpowiedź wraz z kolorowym paskiem stosunku, wykresem kołowym oraz objaśnieniem kroku po kroku.
Przykłady Zadań z Rozwiązaniami Krok po Kroku
Oto 3 przykładowe zadania z pełnym opisem kroków matematycznych w tym kalkulatorze:
Wejście 1 Drug trial: treated group vs placebo
Wejście 2 Smoking and heart disease (cohort study)
Wejście 3 Calculate NNT for a vaccine
Najczęściej Zadawane Pytania
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.