Prasanna Pokhrel

Some of the common challenges in conducting severity rating in PFMEA are listed below along with some thoughts on how these could be mitigated. 
    1. Understanding the ordinal rating scale: Interpretation of ordinal rating scale may be different from the interpretation of ratio scales and there might be the risk of drawing incorrect assumption. For example if the rating scale gives 3 likely and 6 very likely , in the rating, the impact may be significantly different from that of 2 & 4 and not exactly double the rate (as is the ratio in both the cases). The range, however, may be considered as such if the rating scale is not well explained. The solution is to have detailed discussion on the assessment mechanism including the rating scale.

    2. Different rating scale for different industry: The severity rating scale may have very different implications for example, the rating scale used for healthcare industry will have very different scaling parameters and levels vs insurance industry or automobile industry. This challenge can be addressed by working with the actual team members & the respective functional leaders to design a rating scale which is relevant to the organization.

    3. Difference in interpretations: Even in case of the same rating scale being provided, there could be difference in interpretation of the severity & impact of a possible risk based upon the personal experiences of the person conducting the assessment. The solution in such a situation is to have calibration meetings to ensure that every one is on the same page. 

    4. Cognitive Biases: The challenge in using rating scales and not statistical data in arriving at severity rating is that it may be subject to cognitive biases as follows: 
        a. Only takes in to account "known -unknowns"  & does not plan and design suitable response mechanisms for black swan events & "Unknown-Unknowns)
        b. Availability : People will typically ignore statistical evidence and base their estimates on their memories, which favor the most recent, emotional and unusual events which have a significant impact on them. 
        c. Gambler’s Fallacy: People make the assumption that individual random events are influenced by previous random events which might be spurious correlations and may not have causal relationships.
        d. Optimism bias: People overestimate the probability that positive events will occur for them, in comparison with the probability that these events will occur for other people.
        e. Confirmation bias: People seek to confirm their preconceived notions while  gathering information or deriving conclusions.
        f. Majority: People may go with the assessment of majority to conform with the group at the cost of their objective opinion which may be truer representation but different from the group opinion.  
        g. Self-serving bias: People have a propensity to assign to themselves more responsibility for successes than failures.
        h. Anchoring: People tend to base their estimates on previously derived/ used quantities, even when the two quantities are not related.
        i. Overconfidence: People consistently overestimate the certainty of their forecasts.
        j. Inconsistency: When asked to evaluate the same item on separate occasions, people tend to provide different estimates, despite the fact that the information has not changed.
    Solution in this case is to screen out whether the ratings have been influenced by these biases and inform the participants in advance to consider whether the ratings may have been influenced by such biases. Other mitigation measures could be blind peer rating or benchmark comparison with industry ratings for similar processes. 

    5. Interdependence between causal factors and failure modes: FMEA assumes that each risk is an independent event, whereas there may be a high degree of interdependence between factors which could influence risk rating significantly. Understanding and articulating such interrelationship could be challenging & not considering such impact could mean that the assessment is not representative of the possible risks & the resulting impacts. The way to mitigate this is to have a detailed discussion with all the relevant stakeholders & the process expert in a well-designed structure to ensure that all the risk and their interrelationships are well understood and documented. 
    6. Challenge in considering  the effect on both the customer or the process (assembly/ manufacturing unit). As against DFMEA(Design FMEA) where we look at the effects on the customer , in process FMEA, we will need to consider the impact & hence the severity rating of the failure mode if it impacts both the process & the customers. This is because, the impact of the failure mode in this case will mean the impact on the process or the customer in both the  cases. This leads to more complications in having to consider multiple scenarios. This challenge can be mitigated by taking the higher of the severity rating of the failure modes for other the process or the customer as the severity rating for the causal factor/ failure mode.  
    7. Challenge in deconstructing the impact of Root cause vs. assessing failure mode. Though there is a perspective that in some cases Root Cause and Failure Modes can be used interchangeably, however, if we drill down further, it is evident that root cause analysis is typically conducted post facto (after the event) whereas Failure modes identification happens proactively and will take into account various other factors apart from the proximate cause. The challenge is to ensure that this understanding percolates to the team creating the FMEA document. 
    8. Challenge in ensuring the risk assessment as an ongoing process vs as a single time activity -  Risk assessment (including identification & severity assessment) has to be an ongoing process & not a single point in time activity ( as the severity and impact may show material change in cases where there have been significant changes in either internal or external drivers, process dynamics or in key the environmental factors). The challenge is ensure that the rigor of assessment is maintained & updated with any relevant changes. The solution in this case is to have a monitoring / governance mechanism which will ensure that FMEA is kept as a live document with relevant updates to ensure correct risk rating.   
    9. Challenge in considering the impact due to timescale: E.g. the impact of a risk manifesting immediately may be significantly different from  that which may manifest after some time. The solution would be to conduct time-scale analysis of such risk factors to take into consideration the impacts of recent events and see whether the severity rating could change in such cases.