Progress in science relies in part on generating hypotheses with existing observations and testing hypotheses with new observations. This distinction between postdiction and prediction is appreciated conceptually but is not respected in practice. Mistaking generation of postdictions with testing of predictions reduces the credibility of research findings. However, ordinary biases in human reasoning, such as hindsight bias, make it hard to avoid this mistake. An effective solution is to define the research questions and analysis plan before observing the research outcomes-a process called preregistration. Preregistration distinguishes analyses and outcomes that result from predictions from those that result from postdictions. A variety of practical strategies are available to make the best possible use of preregistration in circumstances that fall short of the ideal application, such as when the data are preexisting. Services are now available for preregistration across all disciplines, facilitating a rapid increase in the practice. Widespread adoption of preregistration will increase distinctiveness between hypothesis generation and hypothesis testing and will improve the credibility of research findings.methodology | open science | confirmatory analysis | exploratory analysis | preregistration P rogress in science is marked by reducing uncertainty about nature. Scientists generate models that may explain prior observations and predict future observations. Those models are approximations and simplifications of reality. Models are iteratively improved and replaced by reducing the amount of prediction error. As prediction error decreases, certainty about what will occur in the future increases. This view of research progress is captured by George Box's aphorism: "All models are wrong but some are useful" (1, 2).Scientists improve models by generating hypotheses based on existing observations and testing those hypotheses by obtaining new observations. These distinct modes of research are discussed by philosophers and methodologists as hypothesis-generating versus hypothesis-testing, the context of discovery versus the context of justification, data-independent versus data-contingent analysis, and exploratory versus confirmatory research (e.g., refs. 3-6). We use the more general terms--postdiction and prediction--to capture this important distinction.A common thread among epistemologies of science is that postdiction is characterized by the use of data to generate hypotheses about why something occurred, and prediction is characterized by the acquisition of data to test ideas about what will occur. In prediction, data are used to confront the possibility that the prediction is wrong. In postdiction, the data are already known and the postdiction is generated to explain why they occurred.Testing predictions is vital for establishing diagnostic evidence for explanatory claims. Testing predictions assesses the uncertainty of scientific models by observing how well the predictions account for new data. Generating postd...

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Progress in science relies in part on generating hypotheses with existing observations and testing hypotheses with new observations. This distinction between postdiction and prediction is appreciated conceptually but is not respected in practice. Mistaking generation of postdictions with testing of predictions reduces the credibility of research findings. However, ordinary biases in human reasoning, such as hindsight bias, make it hard to avoid this mistake. An effective solution is to define the research questions and analysis plan before observing the research outcomes-a process called preregistration. Preregistration distinguishes analyses and outcomes that result from predictions from those that result from postdictions. A variety of practical strategies are available to make the best possible use of preregistration in circumstances that fall short of the ideal application, such as when the data are preexisting. Services are now available for preregistration across all disciplines, facilitating a rapid increase in the practice. Widespread adoption of preregistration will increase distinctiveness between hypothesis generation and hypothesis testing and will improve the credibility of research findings.methodology | open science | confirmatory analysis | exploratory analysis | preregistration P rogress in science is marked by reducing uncertainty about nature. Scientists generate models that may explain prior observations and predict future observations. Those models are approximations and simplifications of reality. Models are iteratively improved and replaced by reducing the amount of prediction error. As prediction error decreases, certainty about what will occur in the future increases. This view of research progress is captured by George Box's aphorism: "All models are wrong but some are useful" (1, 2).Scientists improve models by generating hypotheses based on existing observations and testing those hypotheses by obtaining new observations. These distinct modes of research are discussed by philosophers and methodologists as hypothesis-generating versus hypothesis-testing, the context of discovery versus the context of justification, data-independent versus data-contingent analysis, and exploratory versus confirmatory research (e.g., refs. 3-6). We use the more general terms--postdiction and prediction--to capture this important distinction.A common thread among epistemologies of science is that postdiction is characterized by the use of data to generate hypotheses about why something occurred, and prediction is characterized by the acquisition of data to test ideas about what will occur. In prediction, data are used to confront the possibility that the prediction is wrong. In postdiction, the data are already known and the postdiction is generated to explain why they occurred.Testing predictions is vital for establishing diagnostic evidence for explanatory claims. Testing predictions assesses the uncertainty of scientific models by observing how well the predictions account for new data. Generating postd...

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Scientific research relies on computer software, yet software is not always developed following practices that ensure its quality and sustainability. This manuscript does not aim to propose new software development best practices, but rather to provide simple recommendations that encourage the adoption of existing best practices. Software development best practices promote better quality software, and better quality software improves the reproducibility and reusability of research. These recommendations are designed around Open Source values, and provide practical suggestions that contribute to making research software and its source code more discoverable, reusable and transparent. This manuscript is aimed at developers, but also at organisations, projects, journals and funders that can increase the quality and sustainability of research software by encouraging the adoption of these recommendations.

Scientific evidence should guide the selection of practice for individuals with disabilities. Scientific evidence, however, must be trustworthy to move special education toward greater empirical certainty and more effective policies and practices. Transparency, openness, and reproducibility increase the trustworthiness of evidence. We propose that researchers in special education adopt emerging open-science reforms, such as preprints, data and materials sharing, preregistration of studies and analysis plans, and Registered Reports. Adoption of these practices will require shifts in cultural norms, guidelines, and incentives. We discuss how adopting open-science practices can advance the quality of research and, consequently, policy and practice in special education.

Researchers face many, often seemingly arbitrary, choices in formulating hypotheses, designing protocols, collecting data, analyzing data, and reporting results. Opportunistic use of “researcher degrees of freedom” aimed at obtaining statistical significance increases the likelihood of obtaining and publishing false-positive results and overestimated effect sizes. Preregistration is a mechanism for reducing such degrees of freedom by specifying designs and analysis plans before observing the research outcomes. The effectiveness of preregistration may depend, in part, on whether the process facilitates sufficiently specific articulation of such plans. In this preregistered study, we compared 2 formats of preregistration available on the OSF: Standard Pre-Data Collection Registration and Prereg Challenge Registration (now called “OSF Preregistration,” http://osf.io/prereg/). The Prereg Challenge format was a “structured” workflow with detailed instructions and an independent review to confirm completeness; the “Standard” format was “unstructured” with minimal direct guidance to give researchers flexibility for what to prespecify. Results of comparing random samples of 53 preregistrations from each format indicate that the “structured” format restricted the opportunistic use of researcher degrees of freedom better (Cliff’s Delta = 0.49) than the “unstructured” format, but neither eliminated all researcher degrees of freedom. We also observed very low concordance among coders about the number of hypotheses (14%), indicating that they are often not clearly stated. We conclude that effective preregistration is challenging, and registration formats that provide effective guidance may improve the quality of research.

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