Nonparametric Rank Tests for Independence in Opinion Surveys

Abstract

Nonparametric rank tests for independence between two characteristics are commonly used in many social opinion surveys. When both characteristics are ordinal in nature, tests based on rank correlations such as those due to Spearman and Kendall are often used. The case where some ties exist has already been considered whereas Alvo and Cabilio (1995) have studied the case when there are missing values but no ties in the record. However, it frequently happens that the survey data may contain simultaneously
many tied observations and/or many missing values. A naive approach is to simply discard the missing observations and then to make use of the rank correlations adjusted for ties. This approach would be less powerful as it does not fully utilize the information associated with the incomplete data set. In this article, we generalize Alvo and Cabilio’s notion of distance between two rankings to incorporate tied and missing observations, and define new test statistics based on the Spearman and Kendall rank correlation coefficients.
We determine the asymptotic distribution of the Spearman test statistic and compare its efficiency with the corresponding statistic based on the naive approach. The proposed test is then applied to a real data set collected from an opinion survey conducted in Hong Kong.