Correlation coefficients are a measure of how related two variables are. Pearson correlations are stated using the statistic R and range from 0 to 1 with 1 indicating that the two variables are perfectly related. Pearson correlations assume that the two variables being used are scale variables. Scale variables are things like weight in kilos or salary in pounds, whereby if the figure doubles in size, the quantity represented has also doubled at the same scale. As Milton, Wade and Hopkins (2010) point out, IELTS scores are not scale variables since someone with an OIS 4.0 is not ‘half as proficient’ as someone with OIS 8.0. They suggest using Spearman correlations instead when relating vocabulary test scores and IELTS scores since this correlation does not assume that the variables used are scalable. Therefore, Spearman correlations are used in this study.
