The Relationship and Difference between Probability and Risk

When we talk about probability and risk as they relate to healthcare they are two terms that often get confused and misused. In November 2014 I attended a National Press Club luncheon featuring Anthony Fauci, M.D., director of the National Institute of Allergy and Infectious Diseases (NIAID).[1] I attended Dr. Fauci’s lecture focused on the Ebola outbreak. As a Laboratorian and Health Educator there were many questions that I wanted to pose and gain knowledge on how the world was responding to the outbreak. The response he gave to a question from the audience regarding how his involvement in the research of AIDS the recent Ebola crisis lead to a great commentary on probability and risk.

Dr. Fauci stated “The American public understandably, and this not a criticism, really wants to live in a completely a risk free life. Yet every day we live a life that’s full of risks. The issue is the risks have been with us for so long we don’t pay attention to it very much. When a new risk comes in no matter how small that risk is it captures the attention of the public and they worry more about a risk that’s very, very, very low than they do about a risk that they have been living with forever that’s much higher.”

Dr. Fauci gave example in regard to making policy and recommendations based on the science. He was asked years ago about the risk of contracting HIV/AIDS someone said ‘We should ban gay waiters from waiting in Greenwich Village because the infection rate is so high there and what if a waiter has a cut on their finger and brings to your table your dish of calamari and you happen to have a cut on your finger and pick up the plate that he puts in front of you. Is it possible that you can get HIV?’ Dr. Fauci responded “And the answer is biologically “yeah”, it’s possible but what is the likelihood of it happening? Well, I can say with confidence that the likelihood of it happening in that Greenwich Village restaurant is less than the likelihood of you walking out of the restaurant and getting hit by a bus. So it depends on probability and risk and that’s the thing that we need to keep educating people on and you can’t be 100% risk free.”

According to the ISO Guide 73-Vocabulary and the ISO 31000 standard section 2.1, risk is defined as “effect of uncertainty on objectives”. [2] It was previously defined as Risk “Combination of the probability of occurrence of harm and the severity of that harm” [ISO/IEC Guide 51:1999, definition 3.2]. ISO defines Probability as the “Extent to which an event is likely to occur.” Degrees of -belief about probability can be chosen as classes or ranks, such as rare/unlikely/moderate/likely/almost certain, or incredible/improbable/remote/occasional/probable/frequent. ISO/IEC GUIDE 73:2002

So the two terms are always linked but not synonymous or interchangeable. That is the take home message for Risk in Healthcare – you can never be 100% risk free. We manage risk but we cannot control it. We mitigate risk but there will always be a probability that it will occur. Our focus should not only be on reducing risk but also accepting it. In healthcare we must embrace both risk and probability by being prepared. Not only for our practices and organizations, but most importantly our patients.

1. NPC Luncheon with Dr. Anthony Fauci
2. ISO 31000 - Risk management

Prof. Maria S. Hardy, IMA(ASCP), AHI & CLC(AMT) is CEO of Medical, Laboratory & Technology Consultants in Washington, DC. Being a Global Leader in Scientific and Technical Advising, MLT Consultants has extensive experience in working with International/US government, public and private sectors. MLT Consultants offers Accredited Continuing Medical Education, Medical Facility and Laboratory Accreditation & Compliance Technical Support and Capacity Building Scientific and Technical Advising. Please contact at LinkedIn/Facebook/Twitter @MLTCONSULTANTS

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Comment by Prof. Maria Hardy, IMA(ASCP) on January 27, 2015 at 7:56pm

Exactly Enrique! The fact that we live in this very variable world ensures that we must accept some level of risk. I not too long ago saw a movie about F1 racers and one of the characters portrayed, Niki Lauda, said in the film that he accepts 20% risk each time he entered the race car but nothing more. Even though it was a movie I thought it was a brilliant example of how to not only accept risk as a part of life but also how he thrived professionally in spite of risk. Although he did crash, and thank God survived, he returned to racing at become a Champion again. Risk should not be feared, but always respected.

Comment by Enrique Raul Suarez on January 27, 2015 at 7:06pm

Let me give a simple but not too obvious example of how to reduce anything undesirable such as corruption, high mortality rate, poverty, etc,. To say that you can reduce all of the above one hundred percent as a matter of policy (good intentions) the probability that these policies succeed are literally zero because of the nature of variation. However, if we say we can reduce all of the above at a manageable and acceptable level  because we live in an imperfect and variable world, then these are more realistic policies that can make an impact in whatever you want to reduce that is undesirable.

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