Aims and Hypotheses in Psychology: Directional vs Non-Directional
In standard psychology papers, 96% of first hypotheses are supported. In Registered Reports, where the hypothesis is fixed before any data exist, only…
Category: Research
Sampling Methods in Psychology: 5 Techniques With Examples
In six leading psychology journals, 96% of studies relied on samples from Western industrialised countries, which hold about 12% of the world's popula…
Experimental Design in Psychology: 3 Types With Examples
In a between-subjects experiment, one group of people judged the number 9 to be significantly larger than another group judged 221 (Birnbaum, 1999).
Spearman’s Rho: Formula, Worked Example and Table
Spearman's rho was invented by a psychologist, yet the rank formula Charles Spearman printed in 1904 is not the one students learn today. His version …
Wilcoxon Signed-Rank Test: Formula, Worked Example and Table
In 1945 the chemist Frank Wilcoxon introduced the Wilcoxon signed-rank test in a four-page paper and tried it on Darwin's maize plants. It reached the…
Mann-Whitney U Test: Formula, Worked Example and Table
The Mann-Whitney U test is often described as a test of medians, but it is not one. Two groups with identical medians can still produce a significant …
Chi-Squared Test in Psychology: Formula, Example, Table
For the first twenty-two years of its life, the chi-squared test used the wrong degrees of freedom. Karl Pearson gave a 2x2 table 3 instead of 1, unti…
Levels of Measurement: Nominal, Ordinal and Interval
Levels of measurement decide which statistical test you are allowed to run, and AQA devotes 25 to 30 per cent of the entire Psychology assessment to r…
Which Statistical Test to Use in Psychology: A Decision Guide
In a review of 513 neuroscience papers, of the studies where a particular comparison mattered, 79 used the wrong statistical procedure and only 78 use…
The Sign Test: Formula, Worked Example and Critical Values
In 1710, a royal physician counted London christening records for 82 straight years, found boys outnumbered girls every single year, and published wha…