{"id":735,"date":"2017-03-30T13:39:07","date_gmt":"2017-03-30T13:39:07","guid":{"rendered":"https:\/\/bestpractice.bmj.com\/info\/?page_id=735"},"modified":"2026-01-20T16:32:20","modified_gmt":"2026-01-20T15:32:20","slug":"statistics-calculators","status":"publish","type":"page","link":"https:\/\/bestpractice.bmj.com\/info\/evidence\/ebm-toolbox\/statistics-calculators\/","title":{"rendered":"Statistics calculators"},"content":{"rendered":"<p class=\"lead\">There are numerous statistical calculators available. These should be used as a guide only. Medical and other decisions should NOT be based on the results of these calculators. Although they have been tested, we cannot guarantee the accuracy of their calculations or results.<\/p><br \/>\r\nThe following statistical calculators will be of particular interest:<br \/>\r\n<ul><br \/>\r\n \t<li><a href=\"https:\/\/ebmcalc.com\/BMJ_English_Prod\/OddsRatio.htm\" target=\"_blank\" rel=\"noopener noreferrer\">Odds Ratio and Relative Risk<\/a><\/li><br \/>\r\n \t<li><a href=\"https:\/\/ebmcalc.com\/BMJ_English_Prod\/BenefitIncrease.htm\" target=\"_blank\" rel=\"noopener noreferrer\">Benefit Increase \/ Number Needed to Treat Multicalc<\/a><\/li><br \/>\r\n \t<li><a href=\"https:\/\/ebmcalc.com\/BMJ_English_Prod\/RiskReduc_MC.htm\" target=\"_blank\" rel=\"noopener noreferrer\">Risk Reduction \/ Number Needed to Treat Multicalc<\/a><\/li><br \/>\r\n \t<li><a href=\"https:\/\/ebmcalc.com\/BMJ_English_Prod\/BayesianAnalysis_1.htm\" target=\"_blank\" rel=\"noopener noreferrer\">Bayesian Statistics I MultiCalc<\/a><\/li><br \/>\r\n \t<li><a href=\"https:\/\/ebmcalc.com\/BMJ_English_Prod\/BayesianAnalysis_2.htm\" target=\"_blank\" rel=\"noopener noreferrer\">Bayesian Statistics II MultiCalc<\/a><\/li><br \/>\r\n \t<li><a href=\"https:\/\/ebmcalc.com\/BMJ_English_Prod\/Likelihood.htm\" target=\"_blank\" rel=\"noopener noreferrer\">Likelihood Ratio MultiCalc<\/a><\/li><br \/>\r\n \t<li><a href=\"https:\/\/ebmcalc.com\/BMJ_English_Prod\/NegPredVal.htm\" target=\"_blank\" rel=\"noopener noreferrer\">Negative Predictive Value of a Test<\/a><\/li><br \/>\r\n \t<li><a href=\"https:\/\/ebmcalc.com\/BMJ_English_Prod\/PosPredValue.htm\" target=\"_blank\" rel=\"noopener noreferrer\">Positive Predictive Value of a Test<\/a><\/li><br \/>\r\n<\/ul><br \/>\r\nThe first calculator can be used to assess relative risk <strong>(RR)<\/strong> and whether a treatment has a statistically significant effect. To do this, you need:<br \/>\r\n<ul><br \/>\r\n \t<li>The total number of people randomised to the experimental (treated) group and the total number <strong>(AR)<\/strong> of events in the experimental group <strong>(ART)<\/strong>, plus<\/li><br \/>\r\n \t<li>The total number of people randomised to the control group and the total number <strong>(AR)<\/strong> of events in the control group <strong>(ARC)<\/strong>.<\/li><br \/>\r\n<\/ul><br \/>\r\nSee <a href=\"https:\/\/bestpractice.bmj.com\/info\/toolkit\/learn-ebm\/how-to-calculate-risk\/\" target=\"_blank\" rel=\"noopener\">how to calculate risk<\/a> for further information.<br \/>\r\n<br \/>\r\n<strong>Formulae of risk terms<\/strong><br \/>\r\nAR (absolute risk) = the number of events (good or bad) in treated or control groups, divided by the number of people in that group<br \/>\r\nART = the AR of events in the treatment group<br \/>\r\nARC = the AR of events in the control group<br \/>\r\nRR (relative risk) = ART \/ ARC<br \/>\r\nRRR (relative risk reduction) or RRI (relative risk increase) = (ARC-ART) \/ ARC or 1 &#8211; RR<br \/>\r\nARR (absolute risk reduction) or ARI (absolute risk increase) = ARC &#8211; ART<br \/>\r\nNNT (number needed to treat) or NNH (number needed to harm) = 1 \/ ARR<br \/>\r\n<br \/>\r\nFor the detailed definition of the risk terms used, please see a <a href=\"https:\/\/bestpractice.bmj.com\/info\/toolkit\/ebm-toolbox\/a-glossary-of-ebm-terms\/\" target=\"_blank\" rel=\"noopener\">glossary of EBM terms<\/a>.<br \/>\r\n<br \/>\r\n<em><strong>Content created by BMJ Knowledge Centre<\/strong><\/em>","protected":false},"excerpt":{"rendered":"<p>There are numerous statistical calculators available. These should be used as a guide only. Medical and other decisions should NOT be based on the results of these calculators. Although they have been tested, we cannot guarantee the accuracy of their calculations or results. The following statistical calculators will be of particular interest: Odds Ratio and [&hellip;]<\/p>\n","protected":false},"author":3,"featured_media":0,"parent":808,"menu_order":13,"comment_status":"closed","ping_status":"closed","template":"marketing_new.php","meta":{"_acf_changed":false,"footnotes":""},"class_list":["post-735","page","type-page","status-publish","hentry"],"acf":{"components":[{"choose_component":"generic","hide":"","logged_in":["yes"],"logged_out":"","grey_background":"","background_color":"","background_image":null,"title_text_color":"","title":"Statistics calculators","text":"<h1 class=\"lead\">There are numerous statistical calculators available. These should be used as a guide only. Medical and other decisions should NOT be based on the results of these calculators. Although they have been tested, we cannot guarantee the accuracy of their calculations or results.<\/h1>\r\nThe following statistical calculators will be of particular interest:\r\n<ul>\r\n \t<li><a href=\"https:\/\/ebmcalc.com\/BMJ_English_Prod\/OddsRatio.htm\" target=\"_blank\" rel=\"noopener noreferrer\">Odds Ratio and Relative Risk<\/a><\/li>\r\n \t<li><a href=\"https:\/\/ebmcalc.com\/BMJ_English_Prod\/BenefitIncrease.htm\" target=\"_blank\" rel=\"noopener noreferrer\">Benefit Increase \/ Number Needed to Treat Multicalc<\/a><\/li>\r\n \t<li><a href=\"https:\/\/ebmcalc.com\/BMJ_English_Prod\/RiskReduc_MC.htm\" target=\"_blank\" rel=\"noopener noreferrer\">Risk Reduction \/ Number Needed to Treat Multicalc<\/a><\/li>\r\n \t<li><a href=\"https:\/\/ebmcalc.com\/BMJ_English_Prod\/BayesianAnalysis_1.htm\" target=\"_blank\" rel=\"noopener noreferrer\">Bayesian Statistics I MultiCalc<\/a><\/li>\r\n \t<li><a href=\"https:\/\/ebmcalc.com\/BMJ_English_Prod\/BayesianAnalysis_2.htm\" target=\"_blank\" rel=\"noopener noreferrer\">Bayesian Statistics II MultiCalc<\/a><\/li>\r\n \t<li><a href=\"https:\/\/ebmcalc.com\/BMJ_English_Prod\/Likelihood.htm\" target=\"_blank\" rel=\"noopener noreferrer\">Likelihood Ratio MultiCalc<\/a><\/li>\r\n \t<li><a href=\"https:\/\/ebmcalc.com\/BMJ_English_Prod\/NegPredVal.htm\" target=\"_blank\" rel=\"noopener noreferrer\">Negative Predictive Value of a Test<\/a><\/li>\r\n \t<li><a href=\"https:\/\/ebmcalc.com\/BMJ_English_Prod\/PosPredValue.htm\" target=\"_blank\" rel=\"noopener noreferrer\">Positive Predictive Value of a Test<\/a><\/li>\r\n<\/ul>\r\nThe first calculator can be used to assess relative risk <strong>(RR)<\/strong> and whether a treatment has a statistically significant effect. To do this, you need:\r\n<ul>\r\n \t<li>The total number of people randomised to the experimental (treated) group and the total number <strong>(AR)<\/strong> of events in the experimental group <strong>(ART)<\/strong>, plus<\/li>\r\n \t<li>The total number of people randomised to the control group and the total number <strong>(AR)<\/strong> of events in the control group <strong>(ARC)<\/strong>.<\/li>\r\n<\/ul>\r\nSee <a href=\"https:\/\/bestpractice.bmj.com\/info\/evidence\/learn-ebm\/how-to-calculate-risk\/\" target=\"_blank\" rel=\"noopener\">how to calculate risk<\/a> for further information.\r\n\r\n<strong>Formulae of risk terms<\/strong>\r\nAR (absolute risk) = the number of events (good or bad) in treated or control groups, divided by the number of people in that group\r\nART = the AR of events in the treatment group\r\nARC = the AR of events in the control group\r\nRR (relative risk) = ART \/ ARC\r\nRRR (relative risk reduction) or RRI (relative risk increase) = (ARC-ART) \/ ARC or 1 - RR\r\nARR (absolute risk reduction) or ARI (absolute risk increase) = ARC - ART\r\nNNT (number needed to treat) or NNH (number needed to harm) = 1 \/ ARR\r\n\r\nFor the detailed definition of the risk terms used, please see a <a href=\"https:\/\/bestpractice.bmj.com\/info\/evidence\/ebm-toolbox\/a-glossary-of-ebm-terms\/\" target=\"_blank\" rel=\"noopener\">glossary of EBM terms<\/a>.\r\n\r\n<em><strong>Content created by BMJ Digital Health<\/strong><\/em>","image":null,"qr_image":null,"circular_image":null,"button_text":"Read more","button_url":"https:\/\/bestpractice.bmj.com\/info\/evidence\/ebm-toolbox\/bibliography\/","button2_text":"","button2_url":"","video_embed":"","quote":"","quote_author":"","author_job_title":"","feature_iconsimages":null,"bullets":"none","bullet_text":null,"expiration_date":null,"review_type":"normal","reviews":null,"feature_image_cards":null,"feature_icon_cards":null,"podcast_date":null,"podcast_title":"","podcast_text":"","podcast_embed_script":"","campaign_advert_link":"","monthly":{"show_monthly_tab":false,"strikethrough_price":"","price_text":"","per_month_text":"","vat_text":"","subscribe_button_text":"","subscribe_button_link":""},"annual":{"show_annual_tab":false,"packages":null,"default_price":"","default_strikethrough_price":"","default_per_year_text":"","vat_text":"","subscribe_button_text":"","subscribe_button_link":""},"advisory_panel":null,"article_list_fields":null,"subscription_tab_main_heading":"","subscription_tabs":null,"accordion_for_page":null,"embed_code":"","table_structure":null,"column_two_text":""},{"choose_component":"bulletList","hide":"","logged_in":["yes"],"logged_out":"","grey_background":[],"background_color":"","background_image":null,"title_text_color":"","title":"Related 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