The New Statistics: A How-To Guide.

Estimation, based on effect sizes ( ESs) and confidence intervals ( CIs), is much better than null hypothesis significance testing ( NHST). I refer to estimation and meta-analysis-which is the extension of estimation to multiple studies-as the new statistics. The techniques themselves are not new, but using them would for many psychologists be new, and a highly beneficial advance. I describe a six-step strategy for estimation, which starts with the statement of research questions in terms of 'how large?' questions, rather than the dichotomous hypotheses of NHST. I outline how to use estimation to analyse the two-independent-groups and paired designs, and randomised control trials. I discuss the ES measures Cohen's d and correlation, r, in relation to estimation. I describe how to interpret results published using NHST by visualising the corresponding CIs, and give guidance for adopting the new statistics, even in a world that often still expects NHST. I emphasise the value of figures that display CIs, and describe freely available software running under Microsoft Excel that assists calculation of CIs and preparation of figures. [ABSTRACT FROM AUTHOR]