International Choice Modelling Conference, International Choice Modelling Conference 2015

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Salient attributes in choice experiments
Davide Contu, Elisabetta Strazzera

Last modified: 18 May 2015

Abstract


 

Motivation and aims

The choice modeling literature has experienced a blossom of research aimed at unveiling and modeling different attribute processing strategies. It is widely acknowledged that respondents might adopt different processing strategies when making their choice so as to simplify the decision process (Heiner et al. 1983; Payne et al. 1993). However, as observed by Hensher (2014, p.2), ‘What we do not yet have enough accumulated wisdom on is the identification of a small set of processing rules that might be the best descriptors of the way in which individuals process information in hypothetical (via choice experiments) and real markets.’.

Several extensions of standard discrete choice models have been proposed to take into account different attribute processing strategies. A great deal of studies have been focusing on modeling attribute non-attendance, either using information drawn from respondents, or inferring it from the model estimates (Hensher et al. 2005; Hensher 2006; Hensher et al. 2007; Puckett and Hensher 2008; Hensher and Rose 2009; Puckett and Hensher 2009; Scarpa et al. 2009; Carlsson et al. 2010; Hess and Hensher 2010; Scarpa et al. 2010; Campbell et al. 2011; Hole 2011; Alemu et al. 2013; Colombo et al. 2013; Hess et al. 2013; Hole et al. 2013; Kehlbacher et al. 2013; Kragt et al. 2013; Lagarde 2013; Scarpa et al. 2013).

Another stream of work has investigated the role of lexicographic preferences, assuming respondents choose only on the basis of a specific attribute, level or alternative (Sælensminde 2001; Scott 2002; Rosenberger et al. 2003; Gelso and Peterson 2005; Campbell et al. 2006; Lancsar and Louviere 2006; Hess et al. 2010). Furthermore, Cantillo and Ortúzar (2005) and Swait (2009) have put forward a two-steps elimination by aspect decision strategy, according to which respondents initially eliminate alternatives where attributes do not reach a certain level and, successively, a choice is made among the remaining options.

Another approach is based on the stated importance attached to the attributes. For instance, Balcombe et al. (2014) have proposed to incorporate the stated ranking of the attributes in the utility function using a mixed logit framework, where specific weights are given to the attribute parameters depending on their stated ranking.

This paper aims at contributing to the stream of research devoted to improving and widening the knowledge of heuristics in choice modeling, introducing an hypothesis on the anchoring effect of salient attributes in the choice exercise. In a nutshell, we test the following behavioral hypothesis: when respondents have some difficulty-irrespective of the reason-in making the choice between alternatives, they use a simplifying strategy that consists in conditioning the choice on the attribute that they perceive as the most important. In our model, the individual choice is characterized by a mixture of a fully compensatory behavior and a lexicographic behavior. The latter is the result of a simplifying strategy, or in other words a sort of response bias, rather than of a truly non compensatory preference structure.

If some elicitation effect is present in the choice data it may lead to biased results in the coefficients’ estimates and monetary valuations. This paper provides a framework to detect and properly take into account a potential source of bias, hence leading to more reliable estimates.

Model

We model our behavioral hypothesis employing a constrained latent class framework, with i individuals, alternatives, t choice tasks, k attributes and s segments (or classes). A two-classes mixture model is necessary to allow for the anchoring to salient attributes and the fully compensatory behavior. We define segment S=1 as capturing the former, whereas in S=2 the trade-off between all of the attributes is modeled. An alternative specific constant (ASC_Most) characterizes the deterministic component of the utility function conditioned on segment 1. This constant indicates which of the alternatives contains the salient attribute. Remarkably, after the series of choice tasks, respondents were asked to provide the ranking of the attributes, since in this application we employ attribute stated importance to capture saliency. Instead, the utility function conditioned on segment 2 has the effect of this constant constrained to zero, whereas the coefficients attached to the attributes are estimated. Error terms are assumed to be IID Gumbel.

In a nutshell, each respondent is associated to a segment S=1 with probability α, where only the most important attribute drives the choice; simultaneously he or she is associated to the remaining classes with probability 1-α, where a fully compensatory behavior is allowed. Remarkably, practitioners may be interested in modeling more than two latent segments, jointly modeling the role of salient attributes and preference heterogeneity in a discrete fashion.

Preliminary results

The proposed processing strategy is applied to two datasets concerning preferences towards energy (respectively with 216 and 860 respondents) and comparing its results with standard discrete choice models, including the Multinomial Logit, Latent class and Random Parameters Logit, considering the following:

  • The sign and significance of the coefficient attached to ASC_Most;
  • Goodness of fit measures: Log-likelihood, AIC, AIC3, BIC, CAIC;
  • In-sample predictions;
  • Cross validation predictions;
  • Out of sample predictions.

 

Overall, preliminary results provide evidence supporting our behavioral hypothesis: respondents might be focusing on attributes which are salient for them. Most importantly, failure to take this into account leads to poorer fit and substantially different welfare valuations. 

 

References

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