Regulatory Open Forum

Eric,

You asked if the P1/P2 method from ISO 14971:2007 would help meet the EU-MDR requirements for risk management.

The short answer is NO, they are not related. There are, in theory, two approaches. In one approach, estimate the probability that the hazard situation occurs, then estimate the probability that if the hazardous situation occurs patient or user harm results. Calculate the product to estimate the probability of harm with the stated severity.

In the second case, directly estimate the probability of harm with the stated severity; do not break the estimate into these components.

Regardless of the method, there is nothing that I can see in the EU-MDR that would change based on the method employed. By this I mean either method would satisfy the EU-MDR.

However, there are other issues with the P1/P2 method that, in my opinion, make it impractical.

The implicit assumption is that P1 and P2 are point estimates, so their product is a point estimate. In practice, they are probability distributions, so their "product" is not a simple multiplication.

Also, P1, P2, or their product are not probabilities, but statements of frequency of occurrence. (Once and event happens, its probability of occurrence is 1.)

Because people tend to use powers of 10 in setting the frequency of occurrence, there is an implicit assumption about the resulting distribution. Using Table D.4, it appears, for example, that Occasional means that any frequency of occurrence between 0.0001 and 0.00001 are equally likely to happen. This is a uniform distribution.

In addition, there is a conditional probability, making the calculation a little more difficult.

Even if they were point estimates, each number is small, so their product is smaller. In ISO 14971:2007 Table D.4 a Frequent occurrence is about 1 time in a 1,000 or 0.001. This is the product of P1 and P2. If P1 and P2 were equal, each would be about 0.0316.

I believe that P1/P2 is a wonderful conceptual model. In my risk management course, I teach people to consider the sequence of events leading to the hazardous situation. (In my opinion neither ISO 14971:2007 nor ISO 14971:2019 puts enough emphasis on the sequence of events.) Breaking the sequence of events makes P1 = 0, so the hazardous situation cannot occur so patient or user harm cannot result.

In practice nobody has good estimates for P1 or for P2, so there are no good estimates for their product.

My recommendation is that P1/P2 is a good conceptual model but is not a practical method for calculation.

Eric,

You asked if the P1/P2 method from ISO 14971:2007 would help meet the EU-MDR requirements for risk management.

The short answer is NO, they are not related. There are, in theory, two approaches. In one approach, estimate the probability that the hazard situation occurs, then estimate the probability that if the hazardous situation occurs patient or user harm results. Calculate the product to estimate the probability of harm with the stated severity.

In the second case, directly estimate the probability of harm with the stated severity; do not break the estimate into these components.

Regardless of the method, there is nothing that I can see in the EU-MDR that would change based on the method employed. By this I mean either method would satisfy the EU-MDR.

However, there are other issues with the P1/P2 method that, in my opinion, make it impractical.

The implicit assumption is that P1 and P2 are point estimates, so their product is a point estimate. In practice, they are probability distributions, so their "product" is not a simple multiplication.

Also, P1, P2, or their product are not probabilities, but statements of frequency of occurrence. (Once and event happens, its probability of occurrence is 1.)

Because people tend to use powers of 10 in setting the frequency of occurrence, there is an implicit assumption about the resulting distribution. Using Table D.4, it appears, for example, that Occasional means that any frequency of occurrence between 0.0001 and 0.00001 are equally likely to happen. This is a uniform distribution.

In addition, there is a conditional probability, making the calculation a little more difficult.

Even if they were point estimates, each number is small, so their product is smaller. In ISO 14971:2007 Table D.4 a Frequent occurrence is about 1 time in a 1,000 or 0.001. This is the product of P1 and P2. If P1 and P2 were equal, each would be about 0.0316.

I believe that P1/P2 is a wonderful conceptual model. In my risk management course, I teach people to consider the sequence of events leading to the hazardous situation. (In my opinion neither ISO 14971:2007 nor ISO 14971:2019 puts enough emphasis on the sequence of events.) Breaking the sequence of events makes P1 = 0, so the hazardous situation cannot occur so patient or user harm cannot result.

In practice nobody has good estimates for P1 or for P2, so there are no good estimates for their product.

My recommendation is that P1/P2 is a good conceptual model but is not a practical method for calculation.

Eric,

You asked if the P1/P2 method from ISO 14971:2007 would help meet the EU-MDR requirements for risk management.

The short answer is NO, they are not related. There are, in theory, two approaches. In one approach, estimate the probability that the hazard situation occurs, then estimate the probability that if the hazardous situation occurs patient or user harm results. Calculate the product to estimate the probability of harm with the stated severity.

In the second case, directly estimate the probability of harm with the stated severity; do not break the estimate into these components.

Regardless of the method, there is nothing that I can see in the EU-MDR that would change based on the method employed. By this I mean either method would satisfy the EU-MDR.

However, there are other issues with the P1/P2 method that, in my opinion, make it impractical.

The implicit assumption is that P1 and P2 are point estimates, so their product is a point estimate. In practice, they are probability distributions, so their "product" is not a simple multiplication.

Also, P1, P2, or their product are not probabilities, but statements of frequency of occurrence. (Once and event happens, its probability of occurrence is 1.)

Because people tend to use powers of 10 in setting the frequency of occurrence, there is an implicit assumption about the resulting distribution. Using Table D.4, it appears, for example, that Occasional means that any frequency of occurrence between 0.0001 and 0.00001 are equally likely to happen. This is a uniform distribution.

In addition, there is a conditional probability, making the calculation a little more difficult.

Even if they were point estimates, each number is small, so their product is smaller. In ISO 14971:2007 Table D.4 a Frequent occurrence is about 1 time in a 1,000 or 0.001. This is the product of P1 and P2. If P1 and P2 were equal, each would be about 0.0316.

I believe that P1/P2 is a wonderful conceptual model. In my risk management course, I teach people to consider the sequence of events leading to the hazardous situation. (In my opinion neither ISO 14971:2007 nor ISO 14971:2019 puts enough emphasis on the sequence of events.) Breaking the sequence of events makes P1 = 0, so the hazardous situation cannot occur so patient or user harm cannot result.

In practice nobody has good estimates for P1 or for P2, so there are no good estimates for their product.

My recommendation is that P1/P2 is a good conceptual model but is not a practical method for calculation.

Eric,

You asked if the P1/P2 method from ISO 14971:2007 would help meet the EU-MDR requirements for risk management.

The short answer is NO, they are not related. There are, in theory, two approaches. In one approach, estimate the probability that the hazard situation occurs, then estimate the probability that if the hazardous situation occurs patient or user harm results. Calculate the product to estimate the probability of harm with the stated severity.

In the second case, directly estimate the probability of harm with the stated severity; do not break the estimate into these components.

Regardless of the method, there is nothing that I can see in the EU-MDR that would change based on the method employed. By this I mean either method would satisfy the EU-MDR.

However, there are other issues with the P1/P2 method that, in my opinion, make it impractical.

The implicit assumption is that P1 and P2 are point estimates, so their product is a point estimate. In practice, they are probability distributions, so their "product" is not a simple multiplication.

Also, P1, P2, or their product are not probabilities, but statements of frequency of occurrence. (Once and event happens, its probability of occurrence is 1.)

Because people tend to use powers of 10 in setting the frequency of occurrence, there is an implicit assumption about the resulting distribution. Using Table D.4, it appears, for example, that Occasional means that any frequency of occurrence between 0.0001 and 0.00001 are equally likely to happen. This is a uniform distribution.

In addition, there is a conditional probability, making the calculation a little more difficult.

Even if they were point estimates, each number is small, so their product is smaller. In ISO 14971:2007 Table D.4 a Frequent occurrence is about 1 time in a 1,000 or 0.001. This is the product of P1 and P2. If P1 and P2 were equal, each would be about 0.0316.

I believe that P1/P2 is a wonderful conceptual model. In my risk management course, I teach people to consider the sequence of events leading to the hazardous situation. (In my opinion neither ISO 14971:2007 nor ISO 14971:2019 puts enough emphasis on the sequence of events.) Breaking the sequence of events makes P1 = 0, so the hazardous situation cannot occur so patient or user harm cannot result.

In practice nobody has good estimates for P1 or for P2, so there are no good estimates for their product.

My recommendation is that P1/P2 is a good conceptual model but is not a practical method for calculation.