Is the polarization index a valid measure of loyalty for evaluating changes over time?

This paper aims to argue that the polarization index (φ) represents a valid loyalty measure for evaluating changes over time.

The brand performance measures (BPM) are a valid and useful tool for marketing managers in measuring the loyalty consumers attach, in a single time period, to a product or brand. However, the BPM reflect other attributes and not only loyalty. Over time, what might appear to be a change in loyalty may actually be a change in market size or market share. The polarization index (φ) is not biased in this manner and is more appropriate for evaluating changes over time. The study compares the results obtained with three well known BPM utilised for the analysis of loyalty – the purchase frequency, the share of category requirements and the repeat rate – with those obtained with the φ on the purchases of wine made by Italian consumers in the retail sector over two three‐year periods (2003‐2005 and 2006‐2008).

The study shows that the BPM are a fundamental source of information on the loyalty consumers attach to brands and products at one point in time. However, their strong relationship with market share risks providing results that do not reflect actual trends in loyalty. By comparison, φ provides a valid and useful analysis of the ways in which loyalty evolves over time.

Although several researchers have studied the uses of φ on one‐year and three‐year periods, none observed how the index offers more valid results than the BPM over time. The paper shows that marketing managers should always compare the results obtained with the BPM with those derived from the φ before drawing conclusions on the real loyalty trends of their products and brands.