§ 1. Need of a very easy, but yet precise, method of measuring correlation.§ 2. Necessity of comparison by rank, aa absolute nzeasurements $ 3. Existing methods of calculating correlation.The stmdwrd Various methods proposed by mathematicians and in-Estimate by intuition is vague and illusive.are not properly comparable with one another.' r ' method.vestigators respectively.$ 4. Proposed e c ~~y 6 R' method, with am adud illzcstratian.Usage of the 'probable error.'The two kinds of probable errors.§ 5. Relation of the R to the r method.Latter can be simplt$ed, and then only dz$ers from f w m r in that certain data are squared.r = sin -R .Evidence that psychological correlations approximate to one constant form, and therefore are really measurable by a single coeflcient.Summary. G >Appendix.Mathmatical proofs in szcpport of the R method.5 1.Need of a 'footrule' f o r correlation.' skew' correlation.Some continental mathematicians have recently endeavoured to express correlations more accurately by means of a series of terms, instead of a single one.Not only is the calculation more tedious than ever, but even the results are of very doubtful serviceability in actual research.
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C. Spearman (1906) studied this question.