ConLeznporaxy Issues inOecision M3king K. Borcherding, 0.1. Larichev & OM. Messick (Editors) @ Elsevier Science Publishers E.V. (Norlh.Holland), 1990 149 PREFERENCE JUOGMENTS i~ND CHOICE: IS THE PROMINENCE EFFEGT 005 TO INFORI4ATION INTEGRATION OR INFOR&4ATION EVALUATION? Henry Montgomery Tormny Gårling Dept. of Psychology Dept. of Psyehiogy University of Göteborg University of Urneå Gëteborg, Sweden Urnei, Sweden s Erik Lindberg Marcus Selart Dept. of Psychology Dept. of Psychology University of Umei University of Göteborg Uzneå, Sweden Göteborg, Sweden 1. INTRODUCTION People are constantly faced with the need to make preference judgmnents of objects or acts. Sometimes, the preferences concern options in a choice situation. In decision theory it has been taken for granted that choice and preference are ciosely intertwined inasmuch as choice is seen as equivalent to selecting the most preferred option from an offered set of alternatives. However, several studies have shown that preference is not necessarily synonymous with choice. In particular, the most preferred object from a set of objects presented in a non-choice context is not necessarily chosen when the same objects are options in a choice situation (Lichtenstein & Slovic, 1971, 1973; Tversky, Sattah, & Slovic, 1988) . Recently, the present authors have run a series of studies on hos.. preferences differ from choice. We have found repeatedly that choice is less predictable than preference from a combined multi-attribute and expectancy-value model (e. g., Lindberg, Gärling, & Montgomery, 1988, 1989a, 1989b) . In a recent paper we tested two possible explanations for this finding (Lindberg, Gärling, Montgomery, 1989a) . The first possibility was that choice subjects in contrast to preference subjects restructure the given information by modifying their beliefs or values. More precisely, we hypothesized that choice sub~ects attempt to find a dominance structure, i. e., a structure in which one alternative at least approximately dominates other options (Montgomery, 1983) . The second possibility WaS that choice subjects adopt simplifying heuristics for instance by t~king into account only the most important attributes or attributes. The results Supported the second explanation uhereas the dominance structuring hypothesis was not clearly supported by the data. (However, sirnplifying may be seen as one kind of dominance structuring, as noted by Montgomery, 1989.) Our research on the choice-preference discrepancy bears some resemblance to a recent study by Tversky, Sattah, and Slovic (1988) In their study, preferences vere operationalized in terms of a 150 expla;matching procedure in whjch the deca.sa.on maker adjusted ane option witho ta another. It was found that the more prominent dimensjon loomed acros, larger in choice than in matching (see also Slovie, 1975) . Does this for t~ finding -. the prominence effect - also hold if preference is elicited in a more direct way, i. e., through preferenoe judgments of single options? This question is addressed in the present study. is was the 2. case in the Tversky et al study we presented subjects with sets of two options described an two attributes of different importance and 2.1. i asked the subjects to make a choice. However, in difference ta Tversky et al we asked subjects to et'aluate how good ar bad each All ~ option was ss a whole. In our case the prominence effect would imply each that choices more often follow the more important attribute than will was ci be true for the preference judgments. (In the following, the more expressions more/less prominent attribute' and " more/less important attri] attribute' will be used interchangeably.) The 5Assuming that the prominence effect occurs also for preference study judgments and choices, how could it be explained? We think that the Unive: two types of explanations which we offered to account for the combi: differentiaj. predictability of preferences and choices basically are attra applicable also in this rase. One possibility is that choice subjects of tw, evaluate the information about the options differently than optio: preference judgment subjects do. More precisely, they may modify wa5 t their beliefs ar values in such a way that there will be a larger equal, discrepancy between the options on the more important attribute than in thi on the less important attribute. In this way the support for a choice aspec in line with the more prominent attribute will be more consistent. attriJ Both the importance order of the attributes and the differences between the options on the attributes then will speak in favor of a Table choice in line with the more important attribute. The fact that The f making a choice implies. more commitment and conflict than preference 8 the judgments (cf. Abelson & Levi, 1985) may create a greater pressure gradu to find consistent support for choices than for preference judgments. (1988 The other possibility is that choice and preference judgment subjects 1 and differ with respect to how they integrate the given information. that That is, there may be differences with regard to the selection and colunt weighting of the information that is used as a basis for the in th preference judgments and choices, respectively. In line with marke Tversky's et si (1988) discussion of the prominence effect in the attrii case of choice ys. natching iL may be hypothesized that choice in t) subjects in contrast to preference judgment suhjects aften just prese ignore the iess important attribute and simply choose the option which is better on the more important attrjbute. This wouid impiy that choice subjects follow a lexicographic information lntegration rule (Svenson, 1979) . In that case, no modifications of beliefs or values are needed, since there is no conflict in the information on Job x which the choice is based (i. e,, the ordering of the alternatives on the more important attribute) . Job y In the present study we tested these two explanations by asking subjects to evaluate the aspects (e. g., price tevels, skill levels) that uere used for characterizing the options on each of the two 2.2 P attributes. If the prominence effect covaries with these evaluations (i. e., larger discrepancies hetween the evajuations of the aspeets i que: on the more important attribute in choice tasks as compared to group preference judgment tasks and/or vice versa for the less inpoitar.t choic attrihute) then this wouE;d t~ in line with thr, information ovaluation 151 explanation. If on the other hand the prominence effeot 00mars ptzon without any conaomitant varjatjon in the evaluations of aspeots oomed aoross preference judginent and choice tasks this wouid be evidence thns for the information evaluation explanation. cited ingle s the 2. METHOD ts of o and 2.1. Materials ~e to each All subjects were presented with eight sets of two options, where imply each set corresponded to a (potential) choice situation. Eaoh option wili was characterizecj on two attributes, one of which was assumed to be the more important (primary attribute) than the other one (secondary rtarit attribute) . The selection of aspects on the attributes uas guided by a pilot rence study in which ten subjects participated (psyehology students at the t the University of Göteborg) . The aim of the pilot study was to find • the 3 cornbinations of aspects, which rendered the two alternatives equally y are I attractive. Each of the ten subjects was presented with eight sets jects of two options whjcfl differed on two attributes. However, one of the than options was described on only one of the attributes. Subjects' task odify uas to complete the missing aspect so that the two options would be arger egually attractive. This task is identical to the ruatching task used than in tho Tversky et al (1988) study. In the present study, the missing hoice aspect was always the less attractive aspect on the less important tent. L attribute. ences of a j Table 1 sununarizes the eight situations presented to the subjects. that The first column of the table describes the options. In Problems 5- rence 8 the options concerned selection of candidates for jobs or for ssure graduate studies. Three problems were taken from the Tversky et al Pflt5. i (1988) study (Problems 1, 4, and 5) although two of them (Problems jeots 1 and 4) were modified to fit Swedish conditions. (It may be noted ClOfl. that 1 Swedish Crown corresponds to approximately $ 0.15) . The second n and colunn of Table presents the attributes ordered in the same way as the in the guestionnaire. The attribute assumed to be more important is with marked with a *. The third column gives the aspects for each the attribute. Again the information is presented in the same order as horce in the questionnaire. For example, in Problem 2 subjects were just } presented with the following inforrnation. ption imply I ation { Duration in days Salary fs or on on Job x 65 40 000 Cr5. tives 4 Joby 30 20000Crs. sking vels) tWO 2.2 Pr000dure tions pects A questionnaire was adrninistrated to the subjects who served in small :d to J groups. Three versions of the questionnaire uere used, one for xtar~ choices and two for preference judgments. In all questionnaires the atiofi 152 imaçeight sets of two options were presented in identioal tables (see the two exarnp].e above) . Also, in all questionnaires subjeots were asked to sub~ rate each aspect on the attributes with respect to the extent it reqr facilitated orcounteracted what they wanted to attain in the (choice) conc situation. By this formulation we wanted subjects to consider their conc beliefs about the options and not only their values. The ratings were made on 13-point scales ranging from -6 to +6. The endpoints of "juc the scales were defined as TlCounteracts very much" (-6) and on "Facilitates very much" (+6) . Three intermediate scale values were gues defined as "Counteracts partly" (~3), TT~0~5 not influenceTl (0) and abo' "Facilitates partly" (+3) that bad (ma>Table 1 opti Sunimary of Problems Presented to Subjects givE concProblem Mo. ag Options Attributes Aspects bet'. othE l.Benefit plans Payraent in 1 year (5w. Crsj* 10 000 5 000 for profit Payrnent in 4 years (5w. Crs.) 13 000 20 000 sharing In gues2.Tenporary jobs Salary (5w. Crsj* 40 000 20 000 seEs Duration of job (days) 65 30 2.3.3.Restaurants Delicjousness of food (on a 1 for hungry to 100 scoring scale) 62 90 Sig? person Size of portions (grams)* 400 250 GåtE 4.Prograns for Casualties (N of persons)* 650 750 in reducing traffic Cost (5w. Crs. in millions) 450 150 ass, accidents conc The 5.Production Technical knowledge* 86 78 (bus engineers Hunan relations 78 91 (both attributes on a 40 to 100 scoring scale) 3. 6.Applicants to Intelligence* 77 87 3.1. graduate Working capacity 87 73 studies w (both attributes on a 1 to 100 scoring scale) In scol 7.Teachers Knowledge 91 75 to Pedagogic skills* 74 90 att, (both attributes on 1 to 100 jud~ scoring scale) of Fiñ8.Therapeutà Therapeutic skills* on (on a 1 to 100 scoring scale) 90 70 hig~ Working hours 28 38 The*Primary attrabute or 0p~. In the choice condition subjects were asked to choose one of the two sig] options (always denoted as x or y) in each situation. Bach situation onl was described on a separate page. First, i brief background story for rem, the choice was given. In all stories the subjects were asked to 153 ee the imagine that be or she bad to choose between two options. Then the (ed t r two options were desoribed on the two attributes. Thereafter,subjects were asked to rate the aspeets. Finally; the subjects were -. ~ required to indicate their choice. One of the two preference judgxnent.ice) conditions were designed to be as similar as p ssibl to the choice en i condition. The background stories were the same as in the choice ~tings condition except that the word "choosing" was replaced with ats of "judging". Also in this condition the options were presented pairwise and on the same page. Otber differences as compared to the choice were questionnaire were that the instructions for the aspect ratings (see and above) referred to a "situation" and not a lTchoice situation", and that instead of choosing subjects were asked to evaluate how good or bad each option was on a scale ranging from 0 (maximally bad) to 100 (maximally good) . In the other preference judginent condition, each option was presented on a separate page. In the tackground story given on each page only one option was referred to. Hence, in this condition each of the eight situations was referred on two separate pages, one for each of the options. There were always seven pages between the presentations of options frpm the same situation. In all other respects this condition was identical to the first preference 5 000 judgTaent condition. M 000 In all three conditions the order between the pages in the questionnaire was randomized individually for each subject. Each :0 000 session lasted approximately 20 minutes. 2.3. Subjects 90 250 Eighty undergraduate students of psyehology at the University of Göteborg served as subjects. None of these subjects had participated 750 in the pilot study. Thirty-nine, 20, and 21 subjects were randomly 150 assigned to the choice condition, the pairwise preference judginent condition, and separate preference judgment condition, respectively. The subjects were paid with a lottery ticket to the value of $6 (buying price in stores) 3. RESULTS 3.1. Test of the prominence hypotbesis In order to make the choices and preference judgments comparable a score was derived for each pair of options. A score of i was assigned to a pair if the option that was superior on the more important attrjbute was chosen or was associated with a higher preference judgment than was the case for the other option in the pair. A score of 0.5 was assigned when the preference judgments were egual. Finally, a score of0 was assigned when the option that was superior on the less important attribute was chosen or associated with a higher preference judgment. The first three numerical columns of Table 2 present the mean choice or judgment scores (for pairwise and separate presentation of options, respectiveiy) for each problem. It can be seen that two significant prominent effects (p < 0.05, Kruskal) were obtained for ~tion only one of the eight problems. However, for six of the seven j for remaining problems the response pattern was consistent with the d to 154 prominertce effect. That is, for each of these problems choices were more aften in line with the more important attribute than was true ~ for the preference judgrnents. For Problem 3 (restaurants for hungry person) very few subjects chose or judged in line with the attribute assumed to be more important (size of portions) implying that in this case we fajied to create a situation in which the prominence hypothesjs could be tested. fl might be tempting to regard the other Probi, attribute (deliciousness) as primary attribute, which would yield results in line wjth the prominence effect. However, we refrained l.BenE from such post-hoc re-evaluatjons because of the risks for capitalizing on chanoe results. The grand means across all problems except Problem 3 (presented in the bottom row of Table 2) show that 2.Tem! the judgment scores for pairwise judgments tended to fall between the choice scores and the judgment scores for separate judgments. As 3.Res~ shown in Table 2, a one-way ANOVA of means across problems in the three conditions indicated a strongly significant effect regardless 4 ~ of whether Problem 3 was included or not, F(2,77)6.88, p=002 and F(2,77)=8.34, p=0.00l, respectively. In both cases Tukey's test indicated that the difference between choices and pairwise judginents 5.Eng: was marginally significant (p=0.055; p=0.053), whereas the difference between choices and separate judgments was strongly significant 6 Grã (p=0.008; p=0.003) . (For simplicity, in the following we report only tests of grand means that ezcluded Problen 3.) 7 Tom 3.2. Aspect ratings and the prominence effect B.Tha The effects of choices vs preferences on the aspect ratings were assessed by computing for each pair of options the differences across options between the ratings of aspects on the primary and secondary attribute, respectively The differences were always computed by subtracting ratings of the option that was inferior on the primary Grand attribute from the ratings of the option that was superior on that (all attribute. Table 2 gives the means of these differences for each problem and condition. It can be seen that the differences between Note. ratings of the primary attribute covaried significantly (p < .05) value with response conditions for seven of the eight problems, the given exceptional problem being No 3, i. e., the problem for which the prominence effect could not be tested. Across problems these differences were greater for the choice and pairwise preference It judgments than;or separate preference judgments (cf. the grand means judç in Table 2). This covariation was strongly significant, F(2,77) grei 23.415, p = .000, one-way ANOVA. Tukey's test indicated significant in differences between the choice and separate preference judgment Sigt conditions (p = 0.000-) and the pairwise preference and separate prot preference judgment conditions (p 0.000). sec( faci The difforences between the ratings of the secondary attribute were difl not significantly related to response condition for any problem. cOm~ Rowever, across problems there was a significant effect of response sigi conditions, F(2,77) = 3483, p 0.036. The grand means in Table 2 show that the differences on the secondary attribute were greatest Fiñ for pairwise preference judginents and lowest for separate preference and judgments. This was the only discrepancy that was significant cho. according to Tukey's test (p 0.010). resj wjti att. Des were qas true hungry :tribute in this )minence le otber .d yield ~frained :ks for roblerns 0W that .een the nts. As in the ardiess 002 and 5 test dgments ference ificant rt only rs Were ac ro ss Dondary ted by 'rimary )fl that r each ,etween < .05) 5, the ab the these :erence 5 means ,77) = ficant dgment parate e Were oblem. sponse able 2 eatest erence ficant I55 Table 2 Z4eans off Response Scores and Differences Between Ratings off Aspects on Primary and Secondary Attribute Across Options Response scores Diff. between ratings Problem G 92 91 p G P2 P1 p l.Benefit plans .59 .45 .40 .293 4.54 4.52 1.65 .018 2.87 -3.62 -2.15 .446 2.Ternporary jobs .62 .48 .48 .373 3.51 2.57 -0.70 .010 -0.26 -3.24 -0.25 .11.6 3.Restaurants .15 .12 .23 .421 1.67 ,J.91 1.25 .~2 -5.82 -6.62 -4.10 .112 4.Accidents .85 .83 .58 .010 6.00 6.33 1.25 .0~ -2.87 -2.00 -1.95 .me 5.Engineer .54 .48 .38 .476 3.18 2.86 1.25 OL -3.89 -3.14 -2.00 .)fl 6.Graduate .51 .29 .30 .146 3.77 2.91 -0.45 .OL students -3.05 -3.95 -2.25 .~1 7.Teacher .97 .90 .07 .224 5.95 6.00 3.00 OL -2.46 -2.19 -1.40 .349 8.Therapeut .80 .74 .72 .553 5.13 5.81 2.79 .017 -4.26 -5.38 -4.63 .476 Grand mean .70 .60 .53 .001 4.58 4.43 1.09 OL (excl. Problem 3) -2.81 -3.36 -2.08 .036 Grand mean .63 .54 .49 .002 4.22 4.11 1.13 OL (all problems) -3.19 -3.77 -2.11 .039 Nora. C = Choices, P2 Preferences, pairwise, P1 Preferences. separate. p value, Kruskal nr one way ANOVA. Differences between ratings On prinary attribute are given above differences on secondary attribute. It cam also be seen that in the choice and pairwise preference judgment conditions the differences on the primary attribute are greater than on the secondary attribute whereas the reverse is true in the separate preference judgment condition. To assess Ute significance of this pattern Ute mean attribute differences across problems were subjected to a response condition X primary l's. secondary attribute ANOVA (with repeated measures of Ute latter factor) . In tIds analysis the signs of Ute secondary attribute differences were reversed in order to make these differences comparable with Ute differences on the primary attribute. i strongly significant interaction was obtained, F(2r77) = 25,46, p = 0.000. Finally, we will examine the combined impact of response condition and rating differences on the response scores (i. e., preference or chcice scores) . To attain tIds end, we conducted an ANOVA of the mean response scores across problems as a function of response conditions with the mean rating differences on Ute primary and secondary attributes, respectively, ss covariates. The condition factor turned I 156 REFERENCEE out to be non-significant, F(2,75) = 1.602, p =.208, whereas the ~e1son, rating differenoes were strongly related to response scores, F(l,75) Theor~ 19.780, p = .000, and F(l,75) = 11.605, p = .001, respectively. psych flence, the responses scores were not significantly related to LichtenstE response condition independently of the aspect ratings. betwe Exper. Lichtenst~4. DISCUSSION prefe Journ.Our first hypothesis - that the prominence effect will be obtained Lindberg, in choice vs preference judgments - was fully confirrned. Why does and v then this difference exist between choices and preference judgments? choic Is it because people when choosing are more inclined to use Lindberg, simplifying heuristics or is it because they interpret and evaluate predi the given informatjon differently when they are choosing? Our data DeCIS are definitely in favor of the latter hypothesis. The effect of Lindberg, response condition on the scores measuring subjects' tendency to belie respond in favor of primary attribute was almost completely mediated stucly by subjects' evaluations of the aspects. Henne, the data indicate const that the response conditjon affected the evaluations of aspects which Montgomex in turn were the basis for the choice or preference judginent. We did struc not find any direet effect of response condition on the response Hurnpt scores. deci~ 8udãHowever, it should be noted the problems in the present study had the Montgomei simplest possible structure - two options described on two simp: attributes. In more cornplex problems there might be direct effects and I of response task on response scores since the need for simplifying ment,, Ce. g., skipping less important information) may be greater in t4ontgome: choices than in preferences. This is because the task of choosing is domi more complex (the individuaj. needs to compare several options) than 0. s~ the task of making preference judginents (the individual needs only (pp. one to evaluate one option at the time) . In our earlier research on Slovic, the choice-preference discrepancy ve used more complex problems than Jour in the present study. Perhaps this may explain the evidence that was Pen obtained for the simpiifying hypothesis in one of our earlier studies Svenson, (I.indberg, Gärling, & Montgomery, l989a) . onga There is not necessarily a confljct between simplifying and re- Tversky, evaluatjon of given information. Each of these phenomena may OcCur in j• at different stag~s of a decision process (Montgomery & Svenson, 1989). 50w, phenomena may help the individual to find a "good" structure for his or her choice such ss a domjnance structure (Montgornery, 1983). The "good' structures that we have evidenced in the present study may not primarily be characterized as dominance structures but rather as structures where the balance of arguments definitely is in favor of one alternative (importance ordet of attributes and orden of attribute differences favoring the same alternative) . Perhap~, different specifications of what might be meant with a good balance of arguments in a decision situation may make it possible to extend and Coffiplement the domjnance search model. ACKNOWLEDGEMENTS This paper was supported by a grant to the first author from the Swedish Council for Research in the Humanities and Social Sciences. '57 REFERENCES ereas the F(1,75~ Abeison, R. P., & Levi, A. (1985) Decision making and Decision ectjveiy Theory, In G. Lindzey and E. Aronson (Eds.), Randboak at social ~iated to psycholagy (Vol. 2, pp.231-309) . New York: Random House. Lichtenstejn, 3., & Slovjc, 8. (1971). Reversals at preference between bids and ohoices in gantling decisions. Journal off Experi,nental Psycholagy, 89, 46-55. Lichtenstejn, 3., & Slovic, 8. (1973) . Response-induced reversals at preferenoe in garnbling: An extended replication in Las Vegas. obtained Journal off Experimentaj Psychology, 101, 16-20. Why does Lindberg, I., Gärling, T., & Montgornery, H. (1988). Peopie's beliets idgmeñ~~ and values as deterrninants ot housing preterences and simulated to "se choices. Scandinavjan Housing and Planning Research, 5. 181-197. evaluate Lindberg, E., Gärling, T., & Montgomery, 3. (198~a) . Differential Our data predictability of preferences and choice. Journal at Behavioral ffect at Decjsjon Making, 2, 205-219. dency to Lindberg, 3., Gärling, T., & Montgomery, fl. (1989b) . Subjective mediated beiief-value struotures an determinants at consurner behavior: A indicate study at housing preferences and simulated choioes. Journai off •ts whjoh Consvnier Policy, 12, 119-137. • Pe did Montgomery, 3. (1983) . Deoision rules and the search for a dorninance response structure: Towards a process modei ot decision niaking. In 8. C. Humphreys, 0. Svenson, and A. Van (Eds.), .Analyzing and aiding decision processes (pp. 343-369). Amsterdam: North Hoiland and had the Budapest: Academio Press Hungary. on two Mantgomery, H. (1989). The search for a dominanoe structure: etfects Smmplification and elaboratjon in decision making. In D. Vickers iifying and 8. L. Smith (Eds.), Human intarmatian pracessing: Measures, ster in mechanisms, and models (pp. 471-483). Amsterdam: North Holiand. sing is Montgomery, fl., & Svenson, 0. (1989) . A think-aioud study at ) than dominanoe structuring in decisjon processes. In fl. Mantgomery and ds only 0. Svenson (Eds.), Process and structure in human decisian making arch On (pp. 135-151). Chichester: Wiley. ms than Siovic, 8. (1975) . Choice between equaily vaiued alternatives. hat was Jeurnal at Experimental Psychalogy: Human Perception and studies Pertormance, 1, 280-287. Svenson, 0. (1979). Process descriptions at decision making. Organizationai Behavior and Human Pentorniance, 23, 86-112. .nd re- Tversky, A., Sattah, 5., & Slavic, 9. (1988). Contingent weighting occur in judgment and chajce. Psychalogical Review, 95, 371-384. rensan, "gaod" ucture iced in jer at same 7ht be Dn may rnadel. ni the mces.