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.
Formler & Ekvationer som används
Denna Relative Risk Calculator använder 5 kärnekvationer:
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.
Hur man använder denna räknare
För att använda denna Förhållande Räknare, följ 3 steg:
Ange Värden
Skriv in de kända förhållandevärdena i inmatningsfälten. Lämna ett fält tomt — det är det okända värdet som Förhållande Räknaren löser.
Välj Läge
Välj förhållandeläge — Lös, Förenkla eller Skala. Varje läge tillämpar olika ekvationer på dina inmatningsvärden.
Få Resultat
Klicka på Beräkna. Resultatskärmen visar svaret med ett visuell förhållandestapel, cirkeldiagram och steg-för-steg-lösningsuppdelning.
Exempelproblem & Steg-för-steg-lösningar
Här är 3 exempelproblem med steg-för-steg-lösningar som använder denna Förhållande Räknare:
Inmatning 1 Drug trial: treated group vs placebo
Inmatning 2 Smoking and heart disease (cohort study)
Inmatning 3 Calculate NNT for a vaccine
Vanliga Frågor
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.