The replication crisis (or replicability crisis) refers to a methodological crisis in science, in which scientists have found that the results of many scientific experiments are difficult or impossible to replicate on subsequent investigation, either by independent researchers or by the original researchers themselves. Since the reproducibility of experiments is an essential part of the scientific method, this has potentially grave consequences for many fields of science in which significant theories are grounded on experimental work which has now been found to be resistant to replication.
The replication crisis has been particularly widely discussed in the field of psychology (and in particular, social psychology) and in medicine, where a number of efforts have been made to re-investigate classic results, and to attempt to determine both the validity of the results, and, if invalid, the reasons for the failure of replication.
According to 2016 pool on 1,500 scientists 70% of them failed to reproduce another scientist's experiments (50% failed to reproduce their own experiment). These numbers differ among disciplines:
- chemistry: 90% (60%),
- biology: 80% (60%),
- physics and engineering: 70% (50%),
- medicine: 70% (60%),
- Earth and enviroment science: 60% (40%).
In 2009 2% of scientists admitted to falsify study at least once and 14% admitted to personally know someone who did. Misconducts were reported more frequently by medical researchers than others.
Out of 49 medical studies from 1990-2003 with more than 1000 citations 45 claimed that studied therapy was effective. Out of these studies 16% were contradicted by subsequent studies, 16% inflated effectivness of therapy and 24% were not replicated. Food and Drug Administration in 1977-90 found flaws in 10–20% of medical studies.In a paper published in 2012 Glenn Begley, a biotech consultant working at Amgen, and Lee Ellis at the University of Texas argued that only eleven per cent of the pre-clinical cancer studies could be replicated.
Replication failures are not unique to psychology and are found in all fields of science. However, several factors have combined to put psychology at the center of controversy. Much of the focus has been on the area of social psychology, although other areas of psychology such as clinical psychology have also been implicated.
Firstly, questionable research practices (QRPs) have been identified as common in the field. Such practices, while not intentionally fraudulent, involve capitalizing on the gray area of acceptable scientific practices or exploiting flexibility in data collection, analysis, and reporting, often in an effort to obtain a desired outcome. Examples of QRPs include selective reporting or partial publication of data (reporting only some of the study conditions or collected dependent measures in a publication), optional stopping (choosing when to stop data collection, often based on statistical significance of tests), p-value rounding (rounding p-values down to .05 to suggest statistical significance), file drawer effect (nonpublication of data), post-hoc storytelling (framing exploratory analyses as confirmatory analyses), and manipulation of outliers (either removing outliers or leaving outliers in a dataset to cause a statistical test to be significant). A survey of over 2,000 psychologists indicated that a majority respondents admitted to using at least one QRP. False positive conclusions, often resulting from the pressure to publish or the author's own confirmation bias, are an inherent hazard in the field, requiring a certain degree of skepticism on the part of readers.
Secondly, psychology and social psychology in particular, has found itself at the center of several scandals involving outright fraudulent research, most notably the admitted data fabrication by Diederik Stapel as well as allegations against others. However, most scholars acknowledge that fraud is, perhaps, the lesser contribution to replication crises.
Third, several effects in psychological science have been found to be difficult to replicate even before the current replication crisis. For example the scientific journal Judgment and Decision Making has published several studies over the years that fail to provide support for the unconscious thought theory. Replications appear particularly difficult when research trials are pre-registered and conducted by research groups not highly invested in the theory under questioning.
These three elements together have resulted in renewed attention for replication supported by Kahneman. Scrutiny of many effects have shown that several core beliefs are hard to replicate. A recent special edition of the journal Social Psychology focused on replication studies and a number of previously held beliefs were found to be difficult to replicate. A 2012 special edition of the journal Perspectives on Psychological Science also focused on issues ranging from publication bias to null-aversion that contribute to the replication crises in psychology In 2015, the first open empirical study of reproducibility in Psychology was published, called the Reproducibility Project. Researchers from around the world collaborated to replicate 100 empirical studies from three top Psychology journals. Fewer than half of the attempted replications were successful at producing statistically significant results in the expected directions, though most of the attempted replications did produce trends in the expected directions.
Scholar James Coyne has recently written that many research trials and meta-analyses are compromised by poor quality and conflicts of interest that involve both authors and professional advocacy organizations, resulting in many false positives regarding the effectiveness of certain types of psychotherapy.
The replication crisis does not mean that psychology is unscientific. Rather this process is a healthy if sometimes acrimonious part of the scientific process in which old ideas or those that cannot withstand careful scrutiny are pruned, although this pruning process is not always effective. The consequence is that some areas of psychology once considered solid, such as social priming, have come under increased scrutiny due to failed replications. The British Independent newspaper wrote that the results of the reproducibility project show that much of the published research is just "psycho-babble".
Nobel laureate and professor emiritus in psychology Daniel Kahneman argued that the original authors should be involved in the replication effort because the published methods are often too vague. Some others scientists, like Dr. Andrew Wilson disagree and argue that the methods should be written down in detail. An investigation of replication rates in psychology in 2012 indicated higher success rates of replication in replication studies when there was author overlap with the original authors of a study  (91.7% successful replication rates in studies with author overlap compared to 64.6% success replication rates without author overlap).
Replication rates in psychology
A report by the Open Science Collaboration in August 2015 that was coordinated by Brian Nosek estimated the reproducibility of 100 studies in psychological science from three high-ranking psychology journals. Overall, 36% of the replications yielded significant findings (p value below .05) compared to 97% of the original studies that had significant effects. The mean effect size in in the replications was approximately half the magnitude of the effects reported in the original studies.
The same paper examined the reproducibility rates and effect sizes by journal (Journal of Personality and Social Psychology [JPSP], Journal of Experimental Psychology: Learning, Memory, and Cognition [JEP:LMC], Psychological Science [PSCI]) and discipline (social psychology, cognitive psychology). Study replication rates were 23% for JPSP, 38% for JEP:LMC, and 38% for PSCI. Studies in the field of cognitive psychology had a higher replication rate (50%) than studies in in the field of social psychology (25%).
An analysis of the publication history in the top 100 psychology journals between 1900 and 2012 indicated that approximately 1.6% of all psychology publications were replication attempts. Articles were considered a replication attempt if the term "replication" appeared in the text. A subset of those studies (500 studies) was randomly selected for further examination and yielded a lower replication rate of 1.07% (342 of the 500 studies [68.4%] were actually replications). In the subset of 500 studies, analysis indicated that 78.9% of published replication attempts were successful. The rate of successful replication was significantly higher when at least one author of the original study was part of the replication attempt (91.7% relative to 64.6%).
- "Independent, direct replications of others’ findings can be time-consuming for the replicating researcher
- "[Replications] are likely to take energy and resources directly away from other projects that reflect one’s own original thinking
- "[Replications] are generally harder to publish (in large part because they are viewed as being unoriginal
- "Even if [replications] are published, they are likely to be seen as 'bricklaying' exercises, rather than as major contributions to the field
- "[Replications] bring less recognition and reward, and even basic career security, to their authors"
For these reasons the authors advocated that psychology is facing a disciplinary social dilemma, where the interests of the discipline is at odds with the interest of the individual researcher.
Causes of the crisis
In a work published in 2015 Glenn Begley and John Ioannidis offer five bullets as to summarize the present predicaments:
- Generation of new data/ publications at an unprecedented rate.
- Compelling evidence that the majority of these discoveries will not stand the test of time.
- Causes: failure to adhere to good scientific practice & the desperation to publish or perish.
- This is a multifaceted, multistakeholder problem.
- No single party is solely responsible, and no single solution will suffice.
If fact some predictions of a possible crisis in the quality control mechanism of science can be traced back several decades, especially among scholars in science and technology studies (STS). Derek de Solla Price – considered the father of scientometrics – predicted that science could reach ‘senility’ as a result of its own exponential growth. Some present day literature seems to vindicate this 'overflow' prophesy, lamenting at decay in both attention and quality. 
Philosopher and historian of Science Jerome R. Ravetz predicted in his 1971 book Scientific knowledge and its social problems that science - in moving from the little science made of restricted communities of scientists to big science or techno-science - would suffer major problems in its internal system of quality control. Ravetz anticipated that modern science's system of incentive might become dysfunctional (the present 'publish or perish' challenge). For Ravetz quality in science is maintained when there is a community of scholars linked by norms and standards, and willing to stand by these.
Historian Philip Mirowski offered more recently a similar diagnosis in his 2011 book ‘Science Mart’ (2011). 'Mart' is here a reference to the retail giant 'Wall Mart' and an allusion to the commodification of science. In the analysis of Mirowski when science becomes a commodity being traded in a market its quality collapses. Mirowski argues his case by tracing the decay of science to the decision of major corporations to close their in house laboratories in order to outsource their work to universities, and subsequently to move their research away from universities to even cheaper contract research organization (CRO).
The crisis of science's quality control system is affecting the use of science for policy. This is the thesis of a recent work by a group of STS scholars, who identify in 'evidence based (or informed) policy' a point of present tension.
Addressing the replication crisis
Replication has been referred to as "the cornerstone of science". Replication studies attempt to evaluate whether published results reflect true findings or false positives. The integrity of scientific findings and reproducibility of research are important as they form the knowledge foundation on which future studies are built.
- A recent innovation in scientific publishing to address the replication crisis is through the use of registered reports. The registered report format requires authors to submit a description of the study methods and analyses prior to data collection. Once the method and analysis plan is vetted through peer-review, publication of the findings is provisionally guaranteed, based on whether the authors follow the proposed protocol. One goal of registered reports is to circumvent the publication bias toward significant findings that can lead to implementation of QRPs and to encourage publication of studies with rigorous methods.
- Based on coursework in experimental methods at MIT and Stanford, it has been suggested that methods courses in psychology emphasize replication attempts rather than original studies. Such an approach would help students learn scientific methodology and provide numerous independent replications of meaningful scientific findings that would test the replicability of scientific findings. Some have recommended that graduate students should be required to publish a high-quality replication attempt on a topic related to their doctoral research prior to graduation.
- To improve the quality of replications, larger sample sizes than those used in the original study are often needed. Larger sample sizes are needed because estimates of effect sizes in published work are often exaggerated due to publication bias and large sampling variability associated with small sample sizes in an original study.
- Online repositories where data, protocols, and findings can be stored and evaluated by the public seek to improve the integrity and reproducibility of research. Examples of such repositories include the open science framework, http://www.re3data.org/, and www.psychfiledrawer.org. Sites like Open Science Framework offer badges for using open science practices in an effort to incentivize scientists. However, there has been concern that those who are most likely to provide their data and code for analyses are the researchers that are likely the most sophisticated. John Ioannidis at Stanford University suggested that "the paradox may arise that the most meticulous and sophisticated and method-savvy and careful researchers may become more susceptible to criticism and reputation attacks by reanalyzers who hunt for errors, no matter how negligible these errors are."
- The journal Psychological Science has encouraged the preregistration of studies and the reporting of effect sizes and confidence intervals. The editor in chief also noted that the editorial staff will be asking for replication of studies with surprising findings from examinations using small sample sizes before allowing the manuscripts to be published.
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- see also Earp and Trafimow, 2015
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