# Category: Statistics

• ### Does calling a study “under powered” help or hinder criticism?

A common criticism of research (past and present) is that it’s “under powered” or “has low power”. What this typically means is the study doesn’t have many participants (typically between 5 and 40) and so has low statistical power for most effect sizes in psychology . But something being “under powered” only makes sense when…

• ### Should you analyse ordinal data like interval or ratio data?

A couple of months ago, I wrote a summary of a recent paper arguing you shouldn’t analyse ordinal data like interval or ratio. If you do so, there’s a risk of inflated Type I and Type II error rates, as well as reduced power [zotpressInText item=”{VD8XETGZ}”][note]Open access version here[/note]. In response, Helen Wauck wrote a…

• ### Should you calculate a p-value when there isn’t randomisation?

The thought behind this question was prompted by reading [zotpressInText item=”{TIBTBKWD}” format=”%a% (%d%, %p%)”], which argues against frequentist inferential statistics. One of the arguments refers to an underlying assumption required to compute p-values; they need random sampling. Without this, a p-value is meaningless. But this is rare in social science research [zotpressInText item=”{VRZPC486}” format=”%a% (%d%,…

• ### The lazy person’s perspective on programming: why you should code

Lots of people (myself included) bang on about coding. How great it is, how valuable it’s been, etc. You’re probably a bit bored of it. But if you’re not just yet, allow me to explain why it is probably a good idea for you to pick it up. Why am I uniquely qualified to do…

• ### You can’t assume a normal distribution for your data with N>30

The central limit theorem (CLT) is one of the most foundational concepts in all probability (Daly, 2013). It is commonly understood as: when the means of a variable with a suitable number of observations is plotted on a graph, it can form a normal distribution. When the data comes from many independent and random events, the sum…

• ### Essential R packages for education researchers

The intention behind this is to create an updating well of R resources for scientists who focus on education research. If you have any more suggestions please write a comment below or contact me on social media and I’ll add them. Data manipulation and visualization Tidyverse (Sam Parsons)- A collection of packages which allow for comprehensive data…

• ### The positive predictive value/false discovery rate are fundamentally flawed

The positive predictive value (PPV) was brought to a wider audience by JohnÂ Ioannidis in his famous 2005 paper ‘Why Most Published Research Findings Are False’. The related concept false discovery rate (FDR) was popularised by Colquhoun (2014), though the idea it’s based on dates back to Jeffreys (1939). They have become very popular in recent…

• ### Replication and Reproducibility Event II: Moving Psychological Science Forward

On Friday 26th of January at the Royal Society there was a series of talk on how psychology could progress as a science, with an emphasis on replication and reproducibility. I’m going to summarise the key points from the individual talks and make a few comments. A collection of all the individual videos of the…

• ### Why you should think of statistical power as a curve

Statistical power is often defined as “the probability of correctly rejecting H0 when a true association is present” where H0 is the null hypothesis, often an association or effect size of zero (Sham & Purcell, 2014). It is determined by the the effect size you want to detect1, the size of your sample (N), and…

• ### I’m a non-methodologist, does it matter if my p-value definition is wrong?

A few weeks ago, Nature published an article summarising the various measures and counter-measures suggested to improve statistical inferences and science as a whole (Chawla, 2017). It detailed the initial call to lower the significance threshold to 0.005 from 0.05 (Benjamin et al., 2017) and the paper published in response (Lakens et al., 2017). It…