a This is a preprint of a manuscript submitted for publication with Psychonomic Bulletin and Review.In the psychological literature, there are two seemingly different approaches to inference: that from estimation of posterior intervals and that from Bayes factors. We provide an overview of each method and show that a salient difference is the choice of models. The two approaches as commonly practiced can be unified with a certain model specification, now popular in the statistics literature, called spike-and-slab priors. A spike-and-slab prior is a mixture of a null model, the spike, with an effect model, the slab. The estimate of the effect size here is a function of the Bayes factor, showing that estimation and model comparison can be unified. The salient difference is that common Bayes factor approaches provide for privileged consideration of theoretically useful parameter values, such as the value corresponding to the null hypothesis, while estimation approaches do not. Both approaches, either privileging the null or not, are useful depending on the goals of the analyst.Bayes factors | Bayesian estimation | Bayesian inference | ROPE | Hypothesis testing Bayesian analysis has become increasing popular in many fields including psychological science. There are many advantages to the Bayesian approach. Some champion its clear philosophical underpinnings where probability is treated as a statement of belief or information and the focus is on updating beliefs rationally in face of new data (de Finetti, 1974;Edwards, Lindman, & Savage, 1963). Others note the practical advantages-Bayesian analysis often provides a tractable means of solving difficult problems that remain intractable in more conventional frameworks (Gelman, Carlin, Stern, & Rubin, 2004). This practical advantage is especially pronounced in cognitive science where substantive models are designed to account for mental representation and processing. As a consequence, the models tend to be complex and nonlinear, and may include multiple sources of variation (Kruschke, 2011b;Lee & Wagenmakers, 2013;Rouder & Lu, 2005). Bayesian analysis, especially Bayesian nonlinear hierarchical modeling, has been particularly successful at providing straightforward analyses in these otherwise difficult settings (e.g., Rouder, Sun, Speckman, Lu, & Zhou, 2003;Vandekerckhove, Tuerlinckx, & Lee, 2011;Vandekerckhove, 2014).Bayesian analysis is not a unified field, and Bayesian statisticians disagree with one another in important ways (Senn, 2011).
1We highlight here two popular Bayesian approaches that may seem incompatible inasmuch as they provide different answers to what appears to be the same question. We discuss these approaches in the context of the simple problem where there is an experimental and control condition and we wish to characterize the evidence from the data for the presence or absence of an effect.In one approach, termed here the estimation approach, the difference between the conditions is represented by a parameter, 1 Perhaps such disagreements should be ...