This page contains all the collected study materials and instructions from authors that we have compiled. We also include any comments from other contributors or follow up instructions that we have learned since the beginning of the project. Click "read more" below or choose the "Wiki" option above for further information. Contact [Lea Hildebrandt][1], [Danka Puric][2], [TJ Krafnick][3] or [Jordan Wagge][4] (crep.psych@gmail.com) with questions or problems. **Abstract** The 2016 U.S. presidential election brought considerable attention to the phenomenon of "fake news": entirely fabricated and often partisan content that is presented as factual. Here we demonstrate one mechanism that contributes to the believability of fake news: fluency via prior exposure. Using actual fake-news headlines presented as they were seen on Facebook, we show that even a single exposure increases subsequent perceptions of accuracy, both within the same session and after a week. Moreover, this "illusory truth effect" for fake-news headlines occurs despite a low level of overall believability and even when the stories are labeled as contested by fact checkers or are inconsistent with the reader's political ideology. These results suggest that social media platforms help to incubate belief in blatantly false news stories and that tagging such stories as disputed is not an effective solution to this problem. It is interesting, however, that we also found that prior exposure does not impact entirely implausible statements (e.g., "The earth is a perfect square"). These observations indicate that although extreme implausibility is a boundary condition of the illusory truth effect, only a small degree of potential plausibility is sufficient for repetition to increase perceived accuracy. As a consequence, the scope and impact of repetition on beliefs is greater than has been previously assumed. **Notes from the author** The authors noted that the stimuli might be outdated but they would expect the effect to replicate with the original stimulus sets. Stimulus sets (see materials) were obtained from the first author as used in the original study. **Notes from the CREP Team** The aim is to replicate study 2 from the paper. The minimum sample size for the CREP replication is N=100. Please run the direct replication with the original English stimuli. You may decide to add a second sample to the study with translated stimuli (between-subjects manipulation) if the main language in your country is not English. Similarly, the stimuli used relate to the 2016 U.S. election. These stimuli could be potentially outdated and/or not relatable for your participants. **We strongly encourage you to run a second part with updated stimuli** (either within-subjects/after the direct replication with the original stimuli or between-subjects with a second sample). In this case, please make sure to upload the novel stimuli in your OSF repository as well. You may find [this preprint][5] useful in creating up-to-date stimuli. If you plan to conduct a direct+ replication: Please make sure that anything you might add to the study is shown to the participants after the direct replication with the original stimuli and procedure. **Materials** The original stimuli as well as an overview of the procedure (incl. stimulus sets) can be found in the Materials component. Furthermore, the fakenewscrep.study.json is a basic example of the study using [lab.js][6] (you can find further information in the material's wiki). Feel free to use and adapt it, or use any other software that you prefer, such as Qualtrics. The full Pennycook et al. (2018) paper can be accessed [here][7] (may require a library subscription) or [here][8]. Original preregistrations, stimuli and data can be found [in this OSF repository][9]. [1]: mailto:leakhildebrandt@gmail.com [2]: mailto:djaguard@gmail.com [3]: mailto:akrafnick@dom.edu [4]: mailto:crep.psych@gmail.com [5]: https://psyarxiv.com/g69ha [6]: https://labjs.felixhenninger.com/ [7]: https://pubmed.ncbi.nlm.nih.gov/30247057/ [8]: https://gordonpennycook.files.wordpress.com/2020/02/pennycook-cannon-rand-2018.pdf "here" [9]: https://osf.io/txf46/