Thursday, February 23, 2017

Gone: Kahaneman on priming Reconstruction of a Train Wreck: How Priming Research Went off the Rails February 2, 2017Kahneman, Priming, r-index, Statistical Power, Thinking Fast and Slow Authors: Ulrich Schimmack, Moritz Heene, and Kamini Kesavan Abstract: We computed the R-Index for studies cited in Chapter 4 of Kahneman’s book “Thinking Fast and Slow.” This chapter focuses on priming studies, starting with John Bargh’s study that led to Kahneman’s open email. The results are eye-opening and jaw-dropping. The chapter cites 12 articles and 11 of the 12 articles have an R-Index below 50. The combined analysis of 31 studies reported in the 12 articles shows 100% significant results with average (median) observed power of 57% and an inflation rate of 43%. The R-Index is 14. This result confirms Kahneman’s prediction that priming research is a train wreck and readers of his book “Thinking Fast and Slow” should not consider the presented studies as scientific evidence that subtle cues in their environment can have strong effects on their behavior outside their awareness. Introduction In 2011, Nobel Laureate Daniel Kahneman published a popular book, “Thinking Fast and Slow”, about important finding in social psychology. In the same year, questions about the trustworthiness of social psychology were raised. A Dutch social psychologist had fabricated data. Eventually over 50 of his articles would be retracted. Another social psychologist published results that appeared to demonstrate the ability to foresee random future events (Bem, 2011). Few researchers believed these results and statistical analysis suggested that the results were not trustworthy (Francis, 2012; Schimmack, 2012). Psychologists started to openly question the credibility of published results. In the beginning of 2012, Doyen and colleagues published a failure to replicate a prominent study by John Bargh that was featured in Daniel Kahneman’s book. A few month later, Daniel Kahneman distanced himself from Bargh’s research in an open email addressed to John Bargh (Young, 2012): “As all of you know, of course, questions have been raised about the robustness of priming results…. your field is now the poster child for doubts about the integrity of psychological research… people have now attached a question mark to the field, and it is your responsibility to remove it… all I have personally at stake is that I recently wrote a book that emphasizes priming research as a new approach to the study of associative memory…Count me as a general believer… My reason for writing this letter is that I see a train wreck looming.” Five years later, Kahneman’s concerns have been largely confirmed. Major studies in social priming research have failed to replicate and the replicability of results in social psychology is estimated to be only 25% (OSC, 2015). Looking back, it is difficult to understand the uncritical acceptance of social priming as a fact. In “Thinking Fast and Slow” Kahneman wrote “disbelief is not an option. The results are not made up, nor are they statistical flukes. You have no choice but to accept that the major conclusions of these studies are true.” Yet, Kahneman could have seen the train wreck coming. In 1971, he co-authored an article about scientists’ “exaggerated confidence in the validity of conclusions based on small samples” (Tversky & Kahneman, 1971, p. 105). Yet, many of the studies described in Kahneman’s book had small samples. For example, Bargh’s priming study used only 30 undergraduate students to demonstrate the effect. From Daniel Kahneman I accept the basic conclusions of this blog. To be clear, I do so (1) without expressing an opinion about the statistical techniques it employed and (2) without stating an opinion about the validity and replicability of the individual studies I cited. What the blog gets absolutely right is that I placed too much faith in underpowered studies. As pointed out in the blog, and earlier by Andrew Gelman, there is a special irony in my mistake because the first paper that Amos Tversky and I published was about the belief in the “law of small numbers,” which allows researchers to trust the results of underpowered studies with unreasonably small samples. We also cited Overall (1969) for showing “that the prevalence of studies deficient in statistical power is not only wasteful but actually pernicious: it results in a large proportion of invalid rejections of the null hypothesis among published results.” Our article was written in 1969 and published in 1971, but I failed to internalize its message. My position when I wrote “Thinking, Fast and Slow” was that if a large body of evidence published in reputable journals supports an initially implausible conclusion, then scientific norms require us to believe that conclusion. Implausibility is not sufficient to justify disbelief, and belief in well-supported scientific conclusions is not optional. This position still seems reasonable to me – it is why I think people should believe in climate change. But the argument only holds when all relevant results are published. I knew, of course, that the results of priming studies were based on small samples, that the effect sizes were perhaps implausibly large, and that no single study was conclusive on its own. What impressed me was the unanimity and coherence of the results reported by many laboratories. I concluded that priming effects are easy for skilled experimenters to induce, and that they are robust. However, I now understand that my reasoning was flawed and that I should have known better. Unanimity of underpowered studies provides compelling evidence for the existence of a severe file-drawer problem (and/or p-hacking). The argument is inescapable: Studies that are underpowered for the detection of plausible effects must occasionally return non-significant results even when the research hypothesis is true – the absence of these results is evidence that something is amiss in the published record. Furthermore, the existence of a substantial file-drawer effect undermines the two main tools that psychologists use to accumulate evidence for a broad hypotheses: meta-analysis and conceptual replication. Clearly, the experimental evidence for the ideas I presented in that chapter was significantly weaker than I believed when I wrote it. This was simply an error: I knew all I needed to know to moderate my enthusiasm for the surprising and elegant findings that I cited, but I did not think it through. When questions were later raised about the robustness of priming results I hoped that the authors of this research would rally to bolster their case by stronger evidence, but this did not happen. I still believe that actions can be primed, sometimes even by stimuli of which the person is unaware. There is adequate evidence for all the building blocks: semantic priming, significant processing of stimuli that are not consciously perceived, and ideo-motor activation. I see no reason to draw a sharp line between the priming of thoughts and the priming of actions. A case can therefore be made for priming on this indirect evidence. But I have changed my views about the size of behavioral priming effects – they cannot be as large and as robust as my chapter suggested. I am still attached to every study that I cited, and have not unbelieved them, to use Daniel Gilbert’s phrase. I would be happy to see each of them replicated in a large sample. The lesson I have learned, however, is that authors who review a field should be wary of using memorable results of underpowered studies as evidence for their claims. Liked by 18 people Reply 1. Dr. R February 14, 2017 at 8:57 pm Dear Daniel Kahneman, Thank you for your response to my blog. Science relies on trust and we all knew that non-significant results were not published, but we had no idea how weak the published results were. Nobody expected a train-wreck of this magnitude. Hindsight (like my bias analysis of old studies) is 20/20. The real challenge is how the field and individuals respond to the evidence of a major crisis. I hope more senior psychologists will follow your example and work towards improving our science. Although we have fewer answers today than we thought we had five years ago, we still have many important questions that deserve a scientific answer. Dear Daniel Kahneman, there is another reason to be sceptical of many of the social priming studies. You wrote: “I still believe that actions can be primed, sometimes even by stimuli of which the person is unaware. There is adequate evidence for all the building blocks: semantic priming, significant processing of stimuli that are not consciously perceived, and ideo-motor activation. I see no reason to draw a sharp line between the priming of thoughts and the priming of actions.” However, there is an important constraint on subliminal priming that needs to be taken into account. That is, they are very short lived, on the order of seconds. So any claims that a masked prime affects behavior for an extend period of time seems at odd with these more basic findings. Perhaps social priming is more powerful than basic cognitive findings, but it does raise questions. Here is a link to an old paper showing that masked *repetition* priming is short-lived. Presumably semantic effects will be even more transient. Jeff Bowers Liked by 1 person Reply 1. Hal Pashler February 15, 2017 at 4:00 pm Good point, Jeff. One might ask if this is something about repetition priming, but associative semantic priming is also fleeting. In our JEP:G paper failing to replicate money priming we noted “For example, Becker, Moscovitch, Behrmann, and Joordens (1997) found that lexical decision priming effects disappeared if the prime and target were separated by more than 15 seconds, and similar findings were reported by Meyer, Schvaneveldt, and Ruddy (1972). In brief, classic priming effects are small and transient even if the prime and measure are strongly associated (e.g., NURSE-DOCTOR), whereas money priming effects are [purportedly] large and relatively long-lasting even when the prime and measure are seemingly unrelated (e.g., a sentence related to money and the desire to be alone).”