The impact of including images in a conjoint measurement task: evidence from two small-scale studies

In the Netherlands, a large ongoing study seeks to provide insight into the process behind preferences and choices with regard to moving and housing. As part of the development of the survey instrument that was used in this study, we examined whether visual images (such as photographs) should be included, since they may clarify particular attributes (e.g., architectural style) and make the choice task more realistic for the respondents. However, images may disturb the results as respondents may evaluate accidental details on the photographs such as the color of the window frames. This paper presents the results of two subsequent pilot studies on the impact of including images in a web-based questionnaire. In the first study, eight dwelling profiles were presented in three different ways (text only'', text and color photo'' and text and black-and-white impression'') to 28 respondents. In the second study two different instruments were used: one with written information and directly shown photo-collages; the other with written information and photo-collages on request only. Both studies showed that the inclusion of images led to a number of differences between the results obtained with the various presentation methods. These differences may be explained by accidental details on the images. Furthermore, dwelling characteristics appear to be more important to the respondents' overall evaluation of a dwelling when shown with photos than when presented in written format. However, since including images also has a substantial number of benefits, it may not be advisable to leave out images completely from the measurement task. Should images be included in a survey instrument, it is of utmost importance to make sure that all potentially disturbing details are cleared away. Furthermore, it may be better to show a collage of pictures than only one in order to decrease the specific impact of accidental details.