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What fallacies did you encounter as you researched possible causes for the illness

Open in a separate window The animals are genetically modified, bred for a specific trait, or manipulated in some physiological fashion e. Arguing from analogy In research on animal models, scientists sometimes use an approach called the argument from analogy. This involves making inferences about a property of one group, based on observations from a second group, because both groups have some other property in common [ 1 ].

Analogies can be very useful in our daily lives as well as in science: When applying for a job, a person might argue that she would be a good supervisor because she was also a good basketball coach, as the jobs have the property of leadership in common. Concerning animal models, arguing from analogy usually involves making inferences about humans, based on an earlier observation where it was found that the animals and humans have some property in common.

Arguing from analogy is essentially a potentially erroneous judgment based on similarities between entities. However, this does not make the argument invalid by default, because the strength of the argument relies on: Animal models themselves are analogies, as their existence is based on the assumption that they are similar to a target group in some respect.

If the two things we are drawing analogies on are similar enough so that we will reasonably expect them to correlate, an argument from analogy can be strong!

However, when we draw the conclusion that two things share a characteristic, because we have established that they already share another, different characteristic, then we are at risk of making the fallacy of false analogy [ 27 what fallacies did you encounter as you researched possible causes for the illness. The false analogy A false analogy is essentially an instance when an argument based on an analogy is incorrect.

This can occur when the basis of similarity between objects do not justify the conclusion that the objects are similar in some other respect. For instance, if Jack and Jill are siblings, and Jack has the property of being clumsy, we might infer that Jill is also clumsy.

However, we have no information to assert that Jill is clumsy, and the premise for our argument is based solely on the observation that Jack and Jill have genetic properties in common. We are assuming that clumsiness is hereditary, and therefore this is probably a false analogy. Note that knowledge gained later may indicate that—in fact—clumsiness is hereditary, but until we have obtained that knowledge we are operating under assumptions that can lead to false analogies.

The false analogy in animal models With animal models, the false analogy can occur when one group e. For instance, because chimpanzees can follow the gaze of a human, it could be assumed that the non-human primates understand what others perceive, essentially displaying theory of mind [ 28 — 30 ].

However, Povinelli et al. A different example would be birds that are able to mimic human speech: Robbins [ 34 ] pointed out that homology is not guaranteed between humans and primates, even if both the behavioural paradigm and the experimental result are identical for both species: Since an animal model is based on common properties between the animal and humans, we may assume that new knowledge gained from the animal model is also applicable to humans.

In reality, the results are only indicative of evidence in humans. Arguing from analogy, therefore, involves the risk of applying knowledge gained from the animal over to humans, without knowing with certainty if this application is true. Imagine the following line of reasoning: Consequently, we then conduct a different experiment on the animal model, finding result What fallacies did you encounter as you researched possible causes for the illness.

If we assume that B also exist in humans, without trying to recreate these results in human experiments, then we are arguing from analogy, potentially drawing a false analogy. Compared to controls, usually the Wistar Kyoto rat WKYthe SHRs exhibit many of the same behavioural deficits observed in ADHD patients, such as impulsive behaviour [ 37 — 42 ], inattention [ 3537 ], hyperactivity [ 3743 ], and increased behavioural variability [ 44 — 47 ].

One measure of impulsive behaviour is a test involving delay discounting. In this paradigm, participants are faced with the choice of either a small, immediate reinforcer or a larger, delayed reinforcer. Both ADHD patients [ 48 ] and What fallacies did you encounter as you researched possible causes for the illness [ 41 ] tend to show a preference for the smaller reinforcer as the delay between response and reinforcer increases for the large reinforcer. Research on delay discounting with ADHD patients suggests that they are delay averse, meaning that impulsivity is defined as making choices that actively seek to reduce trial length or overall delay rather than immediacy [ 48 — 56 ], but this is usually achieved by choosing a reinforcer with a short delay.

Studies on delay discounting using SHRs tend to manipulate the delay period between response and reinforcer delivery, but do not compare the results with alternative explanations. This is because the rats cannot be told the details of the procedure e. Therefore, most authors who have investigated delay discounting usually avoid the term delay aversion [ 57 ].

However, some authors make the argument from analogy where they assume that the rats show a similar effect to ADHD children: Hayden [ 60 ] has argued that the delay discounting task is problematic in measuring impulsivity in animals because it is unlikely that the animals understand the concept of the inter-trial interval.

Furthermore, if the SHRs were less willing to wait for a reinforcer, then we may argue that this shows immediacy, and not necessarily delay aversion. In this case, it may instead support the dual pathway model of ADHD, which takes into account both delay aversion and an impulsive drive for immediate reward [ 566162 ].

Assuming that the rats are delay averse or impulsive is arguing from analogy. The evidence may only suggests that the rats are impulsive, not necessarily why they are impulsive. If we were to manipulate the magnitude of the large reinforcer then we will also find a change in performance [ 5763 ].

How do we know that the SHRs are sensitive to temporal delays, and not to other changes in the experimental setup, such as the inter-trial interval [ 60 ], reinforcer magnitude [ 63 ], or the relative long-term value of the reward [ 64 ]?

The validity criteria of animal models Before any further discussion on logical fallacies in animal models, the validity criteria of these models must be addressed. We must also point out that there are two approaches to animal model research: When asserting the criteria for validating an putative animal model, the paper by Willner [ 65 ] is often cited, claiming that the criteria for a valid animal model rests on its face, construct, and predictive validity.

This means that the model must appear to show the same symptoms as the human target group face validitythat the experiment measures what it claims to measure and can be unambiguously interpreted construct validityand that it can make predictions about the human population predictive validity. However, there is no universally accepted standard for which criteria must be met in order for an animal model to be considered valid, and the criteria employed may vary from study to study [ 66 — 70 ].

Tricklebank and Garner [ 72 ] have argued that, in addition to the three criteria by Willner [ 65 ], a good animal model must also be evaluated based on how it controls for third variable influences internal validityto what degree results can be generalized external validitywhether measures expected to relate actually do relate convergent validityand whether measures expected to not relate actually do not relate discriminant validity. These authors argue that no known animal model currently fulfils all of these criteria, but we might not expect them to; what is of utmost importance is that we recognize the limitation of an animal model, including its application.

Indeed, it could be argued that a reliable animal model may not need to tick all the validity boxes as long it has predictive validity, because in the end its foremost purpose is to make empirical predictions about its human target group.

Mechanistic validity Behavioural similarities between a putative model and its human target group is not sufficient grounds to validate a model. In other words, face validity is not enough: This is a term that normally refers to the underlying cognitive and biological mechanisms of the behavioural deficits being identical in both animals and humans [ 71 ], though we can extend the definition to include external variables affecting the behaviour, rather than attributing causality to only internal, cognitive events.

Whether the observed behaviour is explained in terms of neurological interactions, cognitive processes, or environmental reinforcement depends on the case in question, but the core of matter is that mechanistic validity refers to the cause of the observed behavioural deficit or symptom.

If we can identify the cause of the observed behaviour in an animal model, and in addition establish that this is also the cause of the same behaviour in humans, then we have established mechanistic validity. This validity criterion does not speak to what has triggered the onset of a condition trigger validityor what made the organism vulnerable to the condition in the first place ontopathogenic validitybut rather what factors are producing the specific symptoms or behaviour [ 71 ].

For instance, falling down the stairs might have caused brain injury trigger validityand this injury in turn reduced dopamine transmission in the brain, which lead to impulsive behaviour. When an animal model is also impulsive due to reduced dopamine transmissions, we have established mechanistic validity even if the trigger was different.

The validity of models of conditions with limited etiology Face validity has been argued to be of relatively low importance in an animal model, because it does not speak about why the behaviour occurs [ 3369 ], i. However, it could be argued that face validity is of higher importance in animal models of ADHD, because the complete etiology underlying the condition is not yet fully known, and therefore an ADHD diagnosis is based entirely on behavioural symptoms [ 73 ].

There is limited knowledge of the pathophysiology on many of the mental illnesses in the Diagnostic and Statistical Manual of Mental Disorders [ 74 ]; depression and bipolar disorder are examples of heterogeneous conditions where animal models have been difficult to establish [ 7576 ]. When dealing with a heterogeneous mental disorder, it is inherently harder for animal models to mimic the behavioural deficits, particularly a range of different deficits [ 7577 — 80 ].

Logical fallacies in animal model research

We could argue, therefore, that mechanistic validity in animal models is difficult, if not impossible, to establish from the outset when our knowledge of causality in humans might be limited.

Models can be holistic or reductionist Animal models can be approached with different applications in mind: A holistic approach assumes that the model is a good representation of the target group as a whole, including all or most symptoms and behavioural or neurological characteristics.

Alternatively, a reductionist approach uses an animal model to mimic specific aspects of a target group, such as only one symptom. This does not mean that the model is not holistic, but rather that its predictive validity is limited to the aspects of autism investigated so far.

The point of this distinction between holistic and reductionist approaches is to underline that animal models have many uses, and falsifying a model in the context of one symptom does not mean the model has become redundant.

As long as the model has predictive validity in one area or another, then it can still generate hypotheses and expand our understanding of the target group, even if the model is not a good representation of the target group as a whole. Indeed, an animal model may actually be treated as holistic until it can be empirically suggested that it should in fact be reductionist.

However, researchers should take care not to assume that a model is holistic based on just a few observations: The exact applications and limitations of an animal model should always be clearly defined [ 3386 ]. Replication involves repeating an experiment using the same methods as the original experiment, while a reproduction involves investigating the same phenomenon using different methods [ 88 ].

Replications assure that the effects are stable, but a reproduction is needed to ensure that the effect was not due to methodological issues. We suggest a third term, reconstruction, which has special applications in animal models. A reconstruction involves redesigning an experiment, while maintaining the original hypothesis, in order to accommodate different species. When an animal experiment aims to investigate a phenomenon previously observed on humans, we have to make certain changes for several reasons.

First, the animals what fallacies did you encounter as you researched possible causes for the illness a different species than humans, and have a different physiology and life experience. Second, the animals do not follow verbal instructions and must often but not always be trained to respond. Third, the experimental setup must often be amended so that a behaviour equivalent to a human behaviour is measured. A fourth observation is that animal studies tend to use smaller sample sizes than human experiments, which makes them more likely to produce large effect sizes when a significant result is found [ 89 ].

An animal model experiment actively attempts to reconstruct the conditions of which we observed an effect with humans, but makes alterations so that we can be relatively certain that an equivalent effect is observed in the animals or vice versa, where a human experiment measures an equivalent effect to what was observed in an animal study.

This questions the construct validity of the study: Another problem concerned with reconstruction is the standardization fallacy [ 90 ]. This refers to the fact that animal experiments are best replicated if every aspect of the experiment is standardized. However, by increasing experimental control we lose external validity, meaning that the results are less likely to apply to other situations [ 91 ].

The difficulty is therefore to find a balance between the two, and finding this balance may depend on the research question we seek to answer [ 3392 ].

  • For instance, because chimpanzees can follow the gaze of a human, it could be assumed that the non-human primates understand what others perceive, essentially displaying theory of mind [ 28 — 30 ];
  • Assuming that the rats are delay averse or impulsive is arguing from analogy;
  • In actuality, this is an occasion that can be used to map the observable characteristics of the animals, which is called phenotyping.

One approach is to initially begin with replications, and if these are successful move on to perform reproductions, and eventually reconstructions. This is essentially what van der Staay, Arndt and Nordquist [ 92 ] have previously suggested: Should the effect persevere, then we have systematically established a higher degree of generalization without losing internal validity.

At the final stage, quasi-replications are conducted using different species, which is similar to our concept of reconstructions, and it is at this stage that the translational value of the findings are evaluated. The double-down effect When we run animal model experiments, we have to use a control group for comparison. When we are evaluating a putative model, we are therefore indirectly evaluating both animal groups for their appropriateness as an animal model for the phenomenon in question, even if we hypothesized beforehand that just one group would be suitable, and this is the double-down effect.

If we were to discover that the control group, rather than the experiment group, shows the predicted characteristic, then it may be tempting to use hindsight bias to rationalize that the result was predicted beforehand, something that should always be avoided! In actuality, this is an occasion that can be used to map the observable characteristics of the animals, which is called phenotyping. This may show that the control group has a property that makes them a suitable candidate as a new putative model.

Follow-up studies can then formally evaluate whether this putative animal model has validity.