Scientific Director @ Welfare Footprint Project
161 karmaJoined Oct 2016Working (15+ years)


  • Attended an EA Global conference


This is an interesting question, relating to the evolutionary role of pain going beyond protection of the individual survival and immediate reproduction (or that of kin), but affecting the group as a whole. As you said, debilitating pain (i.e., pain that prevents individuals to function normally) for a solitary species may also have different moral implications than for a social species even if the unpleasantness of the pain experience is the same.

My impression is that it would be difficult to determine differences in pain aversiveness among species with different degrees of sociality given the confounders present. For example, there might be differences in hedonic and cognitive capacity between social and non-social species (see eg here), hence differences in aversiveness to pain for reasons other than the context of the painful experience.

Thank you for the detailed comments, it is really nice to see you were so thorough with the text and the studies we cite, these are good points!

If we understand you well, with a few exceptions (as in the case of the time trade-off study, [21]), what you mention is that the superlinearity observed could be a by-product of participants of the studies interpreting the designed scales of intensity (even the numerical ones) as not equidistant, hence a non-equidistant plot of aversiveness could, for example, be observed if the relationship between intensity and aversiveness was in fact linear.

My impression, however, is that we are referring to different things when we say pain intensity (and this is our fault for not being clearer on the text, we will make the distinction clearer). My understanding is that ‘pain intensity’ is often used simply as a synonym for aversiveness or unpleasantness, as opposed to physical intensity of stimuli/pain signals. 

As I see it, assessments of pain intensity (unpleasantness) are typically made on what can only be understood as an ordinal scale. Whether evidence on pain unpleasantness is collected with verbal descriptors or numerical descriptors, these unpleasantness scales (i.e. the intensity scales used) can only be interpreted as ordinal exactly because we do not know what type of understanding of the scale study participants have. Even though some authors use the data collected (e.g., pain intensity/unpleasantness ratings in scales from 1-10 or 1-100) and calculate things such as areas under the curve for plots of ‘intensity’ (meant as unpleasantness) ratings x duration, the data is still ordinal for practical purposes and unsuitable for these operations. 

So the effort in this work was to try and see if it would be possible to make such a conversion of pain unpleasantness (from ordinal to ratio scale), and determine the distance among the categories of unpleasantness on a ratio scale. Thus, in the case of the psychophysics studies, I do not see three parameters: intensity of physical stimuli, pain intensity and pain aversiveness, but only two: intensity of physical stimuli and aversiveness (we will correct the text where we mention that the relationship is exponential).

On the availability of studies, unfortunately, all of them were riddled with limitations. Although designs such as the time trade-off approach (used in study [21]) are much better, to our surprise the literature is extremely scarce. So no good studies, and no recent studies either, as far as we are aware. This is why we currently prefer a disaggregated approach, as we do not see how, with the evidence at hand, it is possible to estimate the equivalence weights with any precision .

Yes, I believe the salience of more intense experiences is disproportionally greater, hence the possibly disproportionally stronger memory trace.

On chronic x acute pains, this is our general impression too. With chronic pain there is the possibility of sensitization over time and multiple additional longer-term consequences. 

On memory differences with other species, that is a very interesting question, one for which there is not much research available as far as I am aware. For example, observations of the Peak-End rule mentioned in the text are widespread in humans, but so far there has been only one experiment testing it in animals (dairy cows). That said, at least in vertebrates intense pain has been observed to lead to greater levels of fearfulness, reduced resilience, sensitization, among others (so if it happens early in life, the effects of intense pain are likely much more pervasive). So at least in vertebrates, either memory is present, or intense pain leads to a reconfiguration of pain coping mechanisms.

Sure, we would be glad to review a project like this. Coincidentally, today I came across an EA post where four people from RP articulated their reasons for choosing to present, or not to present, sentience weights for invertebrates. Our rationale for not providing intensity equivalence weights are very much aligned with the views of Jason K, particularly the notion that any weights we use would be overemphasized and reduce our credibility with potential collaborators. That said, we are not advocating for giving up on this area, it is just that we think we are not there yet.

Thanks for your nice words about our work :) . Yes, I see it can be frustrating to have estimates disaggregated (it is very much for us too), and that it can reduce the use and impact of the work. At this moment though we feel it is important to have a solid evidence-based model to quantify animal suffering. That is, a model that is very robust to scrutiny by academics (so they are more likely to adopt it) and by the industry, one in which all estimates can be justified thoroughly.Traction in the academic community is important because as a small team, we would be unable to analyse all situations of animal suffering (in farming context, research, etc) by ourselves, so ideally academics should adopt it too to enable increasing the coverage of the analyses substantially. Robustness against criticisms by the industry is also important to ensure the credibility of this new type of evidence, as used by advocates, in this early stage.  So while we can justify well time in four intensities of suffering, knowledge is not yet available for us to do the same regarding equivalence weights. That said, we have been using summaries of the estimates like "there is a decrease of about 60% of the time in pain for every hen raised in an aviary instead of a cage". Will try to add summaries like this in the forthcoming work, thanks!  

Thanks! I like the idea of a 'minimum transparency rating' policy in the supply chain.

You are absolutely right. From my personal experience in Spain, animal welfare audits are often announced to farmers weeks in advance, so even if they happen (often they only happen in the paper, without the actual visit) farmers have time to correct whatever needs to be corrected, just for the visit. Hence the idea of creating mechanisms to enable auditing by independent parties (other than the companies' own vets or governmental auditors). There is also potential for corruption here, but if there is an organization behind certifing auditors, creating standards for how these audits should happen, or simply reporting the willingness of companies to adhere to these standards (e.g., through a transparency index or something of the sort), the risk could be reduced somehow.

It was a very nice surprise to see the Cumulative Pain method used here to guide this debate. The ‘value tag’ that is already placed on different causes by resource allocation decisions is often based on personal experiences, specialist opinion, tradition or often even empathic guesses. Yet the criteria underlying these decisions are seldom explicit or open to scrutiny. This is one of the things we wanted to help change with the method: to help inform decisions based on an atomized process, where every assumption is explicit, and can help debate in a more objective way, based on estimates and evidence about the actual hedonic experiences of the subjects/targets of the interventions (as is the case here!). The sensitivity app (https://www.pain-track.org/hens) was also created to ensure that anyone disagreeing with our assumptions/estimates could use their own.

Re. the comments:

  • like Michael, for an experience that someone is desperate to stop immediately, similar to “slicing into my leg with a hot, sharp live wire", we would attribute a higher likelihood of Excruciating pain (as this does not seem as something that can be tolerated for a long time). We have not yet estimated any mathematical equivalence between the intensity categories for the reasons we discuss in the FAQ (https://welfarefootprint.org/frequently-asked-questions/), but Excruciating pain is likely much much worse (something similar to an exponential - rather than linear - function) than Disabling pain (we are working on a draft on this issue that should be released at some point this year).
  • You are right that Disabling pain possibly accepts a range of intensities, all fitting the Disabling definition (continuously distressing/disruptive, cannot be ignored, prevents positive welfare, reduces attention to other ongoing stimuli). We have chosen not to create more categories to ensure both resolution and tractability (given the scarcity of evidence typically available from animal studies), but subdivision of the intensity categories is certainly possible and desirable should evidence be available that enables it.
  • It is true that distressed behaviors can be present in the absence of suffering, but this is unlikely to be the case when these behaviors are conditional and proportional to the degree of aversiveness of the situation, and observed along with various other independent indicators of distress.  For example, pre-laying behavior is very different for hens with or without access to a proper nest and excessive pacing (seen in the latter case) is associated with other aversive situations. Other indicators include the observation of inelastic demand for a nest (hens paying increasingly higher costs to get to a nest), the overcoming of aversive obstacles (e.g., narrow gaps, long walking distances, dominant/unfamiliar birds), and vocalizations typically associated with frustration in other contexts. We also need to consider the evolutionary importance of psychological distress in the absence of important resources for survival and reproduction. In the case of physical pain, it is the unpleasantness of the pain experience that protects individuals from provoking further tissue damage when the eliciting stimuli is no longer present. Negative affective states of a more diffuse nature (psychological pain) are similarly strongly selected to ensure that individuals do not give up seeking important resources, as is the case of a nest, mates and offspring.
  • The notion that a hen under higher levels of feed deprivation would work less hard for access to food is a thoughtful one. However, the levels of feed restriction applied where unlikely to deprive the hens from the energy needed to access food. More importantly, evidence has shown the opposite: within the time periods of food deprivation used in experiments (e.g. up to 50-60 hours) hens deprived of food for a longer period work harder than hens deprived of food for a shorter period (e.g. https://www.sciencedirect.com/science/article/abs/pii/0168159190900156)
  • On the extent to which it is possible to compare physical and psychological pain, or use similar criteria to define their intensity, this is an interesting discussion and one that we would also like to work more on. For example, it may be hard to identify,  in the short term, reliable biological markers of psychological suffering, and the same is true for humans. Consider for example the lack of changes in adrenocortical function in prisoners held 10 days in solitary confinement (“Adrenocortical function, as measured by plasma cortisol levels, indicated that solitary confinement was not more stressful than normal institutional life”, https://psycnet.apa.org/doiLanding?doi=10.1037%2Fh0081866), despite the severity of the experience as reported by those who have undergone it. 
  • Thanks for the interesting discussion!