Rev­er­sal test

TagLast edit: 26 May 2021 11:43 UTC by Pablo

The reversal test is a debiasing heuristic for reducing status quo bias. The test was introduced by Nick Bostrom and Toby Ord in a 2006 article (Bostrom & Ord 2006). Although the authors proposed it as a tool for reducing status quo bias specifically in the field of applied ethics, the test is applicable much more generally, to the evaluation of any decision involving a potential deviation from the status quo along some continuous dimension.

The reversal test

Bostrom and Ord define the reversal test as follows (Bostrom & Ord 2006: 664-665):

When a proposal to change a certain parameter is thought to have bad overall consequences, consider a change to the same parameter in the opposite direction. If this is also thought to have bad overall consequences, then the onus is on those who reach these conclusions to explain why our position cannot be improved through changes to this parameter. If they are unable to do so, then we have reason to suspect that they suffer from status quo bias.

The justification for the reversal test is that, since for most parameters only a small fraction of all possible values constitute local optima, the status quo can in most cases be improved upon by deviating from it in one of the two possible directions. Thus, if a deviation in one of these directions is regarded as undesirable, a deviation in the opposite should, absent credible reasons to the contrary, be regarded as desirable.

The authors illustrate the test with an application to cognitive enhancement (Bostrom & Ord 2006: 664):

The great majority of those who judge increases to intelligence to be worse than the status quo would likely also judge decreases to be worse than the status quo. But this puts them in the rather odd position of maintaining that the net value for society provided by our current level of intelligence is at a local optimum, with small changes in either direction producing something worse. We can then ask for an explanation of why this should be thought to be so. If no sufficient reason is provided, our suspicion that the original judgment was influenced by status quo bias is corroborated.

Adam Kolber offers another application of the test to decisions concerning memory enhancement (Kolber 2006: 1610-1611) The test has also been used in discussions about anti-aging research: “if there is merit in the suggestion that too long a life, with its end out of sight and mind, might diminish its worth, one might wonder whether we have already gone too far in increasing longevity.” (President’s Council on Bioethics 2003: 196)

The double reversal test

In addition to the reversal test, Bostrom and Ord proposed a double reversal test (Bostrom & Ord: 673):

Suppose it is thought that increasing a certain parameter and decreasing it would both have bad overall consequences. Consider a scenario in which a natural factor threatens to move the parameter in one direction and ask whether it would be good to counterbalance this change by an intervention to preserve the status quo. If so, consider a later time when the naturally occurring factor is about to vanish and ask whether it would be a good idea to intervene to reverse the first intervention. If not, then there is a strong prima facie case for thinking that it would be good to make the first intervention even in the absence of the natural countervailing factor.

As an example, consider an irreversible medical procedure that prevents a certain poisonous chemical in the water supply from causing mild cognitive impairment. This procedure is widely regarded as desirable because of its protective effects on brain function. Eventually, a technology is developed that completely removes the chemical from the water supply. At this point, the medical procedure, which operates by offsetting cognitive impairment via a commensurate degree of cognitive enhancement, now comes to produce a net increase in cognitive functioning. However, while opponents of human enhancement would object to an intervention that directly conferred this boost in mental ability, they do not believe that in this scenario the chemical should be reintroduced in the water supply, or that cognitive functioning should otherwise impaired. These seemingly inconsistent attitudes suggest that the opposition to human enhancement is not rationally justified, and derives from status quo bias.

An alternative reversal test

The reversal and double reversal tests should be distinguished from a related heuristic that also involves a certain kind of reversal and is also intended to combat status quo bias (Weijers 2011: 10). Whenever a change to the status quo is being considered, this heuristic suggests that the change be reframed as the status quo, and the status quo as the change. For example, a person considering whether to move to a new city could imagine that they are already living in this new city, and consider instead if they would move to the city where they do in fact live (Salamon 2012: 3.2). Or an investor considering whether to sell stocks could instead consider whether they would buy if they did not already had a position.

This alternative reversal test has been applied to Robert Nozick’s “experience machine” thought experiment, considered by many to raise a decisive objection to mental state theories of wellbeing generally and hedonism specifically. (Weijers (2014: 530) lists 30 separate publications expressing this opinion.) Adam Kolber and Joshua Greene have independently suggested considering, besides Nozick’s original question of whether we would connect to the experience machine, the question of whether we would disconnect from it were we already connected (Kolber 1994: 15; Greene 2001). The authors speculate that most people would answer both questions negatively, suggesting that our intuitive responses are being influenced by status quo bias. Subsequent experimental results by Felipe De Brigard and Dan Weijers have on the whole vindicated those speculations (De Brigard 2010; Weijers 2014).


Bostrom, Nick & Toby Ord (2006) The reversal test eliminating status quo bias in applied ethics, Ethics, vol. 116, pp. 656–679.

de Brigard, Felipe (2010) If you like it, does it matter if it’s real?, Philosophical Psychology, vol. 23, pp. 43–57.

Greene, Joshua D. (2001) ‘A psychological perspective on Nozick’s experience machine and Parfit’s repugnant conclusion’, Society for Philosophy and Psychology Annual Meeting, Cincinnati, Ohio.

Hindriks, Frank & Igor Douven (2018) Nozick’s experience machine: an empirical study, Philosophical Psychology, vol. 31, pp. 278–298.

Kolber, Adam J. (1994) Mental statism and the experience machine, Bard Journal of Social Sciences, vol. 3, pp. 10–17.

Kolber, Adam J. (2006) Therapeutic forgetting: the legal and ethical implications of memory dampening, Vanderbilt Law Review, vol. 59, pp. 1559–1626.

The President’s Council on Bioethics (2003) Beyond Therapy: Biotechnology and the Pursuit of Happiness, Washington, D.C.

Salamon, Anna (2012) Checklist of rationality habits, LessWrong, November 7.

Weijers, Dan (2011) ‘Intuitive biases in judgments about thought experiments: the experience machine revisited’, Philosophical Writings, vol. 50, pp. 1–18.

Weijers, Dan (2014) Nozick’s experience machine is dead, long live the experience machine!, Philosophical Psychology, vol. 27, pp. 513–535.

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