A special application of the Chi-squared test (with a different formula) for ordinal data tabulated as a 2xN table. It should be used when the intention is not just to compare the differences between the two groups but to see whether there is a consistent trend towards decrease or increase in the difference between the groups. An example is the association of parental HLA sharing (one-to-four antigens) with fetal loss in a case-control study (those with recurrent miscarriages and normal fertile couples). The Chi-squared test for trend has one degree of freedom. The associated P value obtained by the trend test is always smaller than the corresponding P value of an ordinary Chi-squared test. Thus, it is for the benefit of the researcher to use the trend test where appropriate. Alternative tests for the analysis of trend are Wilcoxon-Mann-Whitney test or the t-test with use of ordered scores. (
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