The Effect of Learning and Fatigue on Preferences and WTP in a ...

the results also show that the value <strong>of</strong> organic production increases significantly. Overall, this
suggests that the learning process makes respondents refine their stated preferences especially for
these two attributes whereas the others are not significantly affected. Importantly, this implies that
the policy advice obtained from the present survey is to some extent dependent on whether we take
learning into account or not.
Assuming that the preferences stated in the last 8 CS are the ones closest to the true preferences 4 ,
then basing policy advice on the first 8 CS will significantly under-estimate the value <strong>of</strong> two <strong>of</strong> the
quality attributes that we are interested in. While the majority <strong>of</strong> the previous studies considering
learning <strong>and</strong> fatigue effects in CE have focused on establishing whether these effects take place,
very few have actually considered the potential impacts on WTP estimates. Hanley et al. (2002)
find only weak evidence <strong>of</strong> learning <strong>and</strong> no significant impact on WTP estimates. This is however
not directly comparable to the internal test we provide here as the results reported in Hanley et al.
(2002) are based on an external test comparing two split samples with respondents answering four
<strong>and</strong> eight CS, respectively. Furthermore, the comparison <strong>of</strong> WTP in their paper represents only a
minor objective in their study <strong>and</strong>, hence, relatively limited information about the actual test is
reported. Another related paper is Johnson & Bingham (2001). In a health economics paper they
report findings from an internal test probably somewhat similar to ours where they compare VTP 5
estimates based on the beginning <strong>and</strong> the end <strong>of</strong> a SP question sequence, respectively. <strong>The</strong>y find no
significant differences. Unfortunately, they report only very limited information about the actual
experimental setup <strong>and</strong> test procedure, so it is difficult to assess the validity <strong>of</strong> their result. Based on
Hanley et al.’s (2002) <strong>and</strong> Johnson & Bingham’s (2001) results researchers might reach the
conclusion that WTP estimates will not be affected by learning <strong>and</strong> fatigue effects, <strong>and</strong>, hence,
4 Even though we do not have real market data available to support this assumption, it seems like a reasonable
assumption considering the fact that preferences have stabilized in accordance with the DPH.
5 VTP is an abbreviation <strong>of</strong> Value To Patients, a concept quite similar to WTP.
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