Paired Preference Tests Research Articles

Application of gamma irradiation to reduce microbial contamination in herbal cosmetic products

This study addresses the decontamination of herbal powder cosmetics by gamma irradiation to reduce the total microbial colony count in facial herbal powder, herbal rose brush on and talcum. Pre-irradiated samples showed total colony counts of 3.00×104, 2.70×104 and 1.00×103CFU/g. At 3rd day after application, irradiation reduced the total colony counts to 1.90×102, 6.00×102 and 1.20×102CFU/g. Moreover, the total colony counts of the three samples were found to be less than 100CFU/g after 3 months storage. The non-uniformity of ΔE⁎ revealed that time affected the color of brush on and talcum, which differed from their original color; however, irradiation affected the colors of the brush on only (P<0.05), by reducing its brightness and increasing redness and yellowness of the products. Paired preference tests were conducted in facial herbal powder and herbal rose brush on. The results showed no significant preferences between the non irradiated and irradiated of the two products at P max=75%, α=0.05, β=0.10. This concludes that the irradiation does not affect the preference of the products, and it can be an alternative technology to reduce microbial decontaminations in herbal products.

Estimation of the Thurstonian model for the 2-AC protocol

The 2-AC protocol is a 2-AFC protocol with a “no-difference” option and is technically identical to the paired preference test with a “no-preference” option. The Thurstonian model for the 2-AC protocol is parameterized by δ and a decision parameter τ, the estimates of which can be obtained by fairly simple well-known methods. In this paper we describe how standard errors of the parameters can be obtained and how exact power computations can be performed. We also show how the Thurstonian model for the 2-AC protocol is closely related to a statistical model known as a cumulative probit model. This relationship makes it possible to extract estimates and standard errors of δ and τ from general statistical software, and furthermore, it makes it possible to combine standard regression modelling with the Thurstonian model for the 2-AC protocol. A model for replicated 2-AC data is proposed using cumulative link mixed models. Examples will be given throughout the paper and the methodology is implemented in the authors’ free R-packages sensR and ordinal.

The Effect of a Flaxseed Oil‐Enhanced Diet on the Product Quality of Farmed Brook Trout (Salvelinus fontinalis) Fillets

The effects of dietary modification with flaxseed oil-enhanced (Flax) feed on the product quality of brook trout fillets were examined. Trout were fed a commercial feed supplemented with fish oil (CD) or flaxseed oil (Flax) for 165 d before harvesting. Proximate composition and fatty acid profile were determined on fillets. Quality parameters of the raw fillets were examined over the storage period by measuring color (L*, a*, b*), muscle pH, and thiobarbituric acid reactive substances test. Evaluations on the cooked fillets included sensory evaluation with triangle tests and a paired preference test. There were no differences in proximate composition between the groups; however, the total omega-3 fatty acids were greater in Flax fillets (P<0.05). Diet and day were shown to interact in their effect on whiteness, pH, and lipid oxidation (P<0.05); however, linear regression did not determine that malondialdehyde concentration was associated with time in either diet type implying that lipid oxidation in the vacuum-packed fish was controlled at storage temperatures (4°C). Sensory panelists were able to choose the odd sample in a replicated triangle test analyzed using the β-binomial model, and there was preference for Flax fillets (P<0.05). Results indicate that a Flax-enhanced diet would have favorable effects on product quality of farmed brook trout.

PAIRED PREFERENCE TESTS: USE OF PLACEBO STIMULI WITH LIKING AND BUYING PREFERENCES

ABSTRACT Besides responses to the target pair of stimuli being tested in a paired preference test, comparison with responses to a putatively identical “placebo” pair can be used for a test of significance, to determine whether the response frequencies elicited by the target pair are different from those that would be obtained had there been no preference. Yet, preference responses elicited by the placebo pair can also be used as a way of identifying consumers who bias avoided the “No preference” option and thus generated biased response. Such consumers can then be eliminated. Yet, using this approach greatly reduces the sample size. However, using some response options associated with purchase intent rather than liking can reduce the number of consumers that are eliminated. This was confirmed for potato chip, milk and orange juice stimuli. From psychology, the concepts of operational preference and types of response bias appropriate to preference testing were introduced and discussed. PRACTICAL APPLICATIONS The measurement of preference and acceptance of foods is important for product development and decisions regarding the launching of new products into the market. The paired preference test has some issues associated with its design and analysis, and these must be considered if preference tests are to give valid and reliable data. One of the problems is that the majority of consumers tend to report preferences even when the stimuli are putatively identical; here, a “No preference” response would seem more appropriate. Such consumers would seem to be reacting to the extraneous conditions of the preference test rather than the sensory characteristics of the putatively identical stimuli under consideration. Such responses could be termed “biased response.” Yet, the consumers' responses to the target (different) stimuli under consideration could be trusted more if the consumers had shown that they did not have this tendency to give “biased responses.” They would show this by selecting a “No preference” response to putatively identical stimuli. This paper shows that the tendency to give “biased response” can be reduced by manipulating the wording of the preference question. This does not furnish a complete solution to the problem but it indicates one possible step toward solution and adds valuable information to the body of knowledge that is being built with a view avoiding the difficulties associated with preference testing.

Consumer acceptance of yellow, provitamin A-biofortified maize in KwaZulu-Natal

Objectives: To assess the acceptance of popular maize food products (phutu, thin porridge and samp), prepared with yellow, provitamin A-biofortified maize varieties, in 212 subjects between the ages of three and 55 years, from rural KwaZulu-Natal.Design: A cross-sectional study.Method: Preschool, primary school and secondary school subjects were randomly selected from two primary schools and one secondary school, respectively, while adult subjects constituted a convenience sample. Pre- and primary school children completed a paired preference test. Secondary school and adult subjects completed a five-point facial hedonic and a preference ranking test. Focus group discussions were conducted using adult subjects.Results: Preschool children preferred yellow maize to white maize food products: phutu (81% vs. 19%; p-value < 0.001), thin porridge (75% vs. 25%; p-value < 0.001) and samp (73% vs. 27%; p-value < 0.001). There was no statistically significant difference in preference for white and yellow maize by primary school children. Secondary school and adult subjects preferred white maize to yellow maize. Focus group discussions confirmed the preference for white maize by the adults.Conclusion: The study findings suggest that yellow, provitamin A-biofortified maize has the potential to succeed as a new strategy of dealing with the serious problem of vitamin A deficiency, especially among children of preschool age. However, in older groups, this strategy is unlikely to be successful, unless other strategies are implemented, including intensive nutrition education programmes on the nutritional benefits of the maize, targeting the market price at which yellow maize is sold, increasing its availability in local grocery stores, and improving its sensory properties through breeding.

Development and sensory evaluation of an improved beverage from Nigeria’s tamarind (tamarindus indica l.) fruit

Tamarind (Tamarindus indica L.), an indigenous underutilised tree fruit, has many valuable properties and almost every part of the tree is utilised by rural and urban dwellers. Nigerian tamarind fruits are grossly underutilised, with the rural dwellers utilising some of the fruits in beverage production using ancient processing methods. The ancient processes of manufacture are cumbersome, slow, non-hygienic and highly subjective, often resulting in non-uniform and low quality products which are less preferred to commercial imported ones. Furthermore, traditional tamarind beverage is not as popular among the populace as other traditional beverages. There is therefore a need to develop simple and affordable process of producing standard tamarind beverage which would be widely accepted by Nigerians. A simple, improved processing method was developed based on the traditional method of manufacturing tamarind beverage using the modified one-factor-at-a-time method to determine the experimental levels of the various ingredients used in the formulation of the beverage. A pilot study was carried out to determine the acceptable range of pulp to water blend. The beverages were evaluated by the paired preference, hedonic rating and multiple comparison tests using 50 semi-trained assessors within the age range of 18 and 45 years. The results of the paired preference tests were expressed as levels of significance while the mean scores of hedonic rating tests were subjected to analysis of variance. Tukey′s test was used to separate the means. Samples of tamarind beverages produced by the traditional and improved processing methods were analysed for colour, pH, total acidity, soluble solids, ascorbic acid, total solids, browning index and cloudiness using standard methods. The colour (A 325nm ), cloudiness (A 660nm ), browning index (A 420nm ) and ascorbic acid (mg/100ml) of the traditional and improved beverages were 0.91±0.25, 0.68±0.16, 1.42±0.04, 9.5±0.69 and 0.60±0.01, 0.13±0.01, 0.19±0.01 and 10.4±0.21, respectively. While the traditional processing method took 10 hours to produce about 10 litres of beverage, the improved processing method took 2 hours to produce 250 litres of beverage. The improved beverage was rated much higher in terms of colour, aroma, taste and overall acceptability than the traditional beverage and compared favourably well with a similar commercial beverage. A beverage with more acceptable qualities than the traditional beverage was thus produced from the improved processing method.

VARIOUS PAIRED PREFERENCE TESTS: EXPERIMENTER EFFECT ON “TAKE HOME” CHOICE

ABSTRACT Three types of paired preference test were performed on a total of 213 consumers. In each test, consumers were required to choose between two types of chocolate. They performed the traditional preference test which measured relative degrees of liking. Also , they performed a “Choosing” preference tests where they were required to specify which of two chocolates they were more likely to choose when offered both or whether they might choose either or neither. They also performed a “Buying” preference tests where they specified which of two chocolates they were more likely to buy or whether they might buy either or neither. After testing, they were able to take away either one type of chocolate or two types of chocolate. For one group of consumers, this was done while the experimenter was not watching; for the other group, the consumers were being observed. Observing the consumers as they selected chocolates to take away had a biasing effect. Correspondence between the three types of test and what consumers took away with them was low. The results were discussed in term of “test” preferences and “operational” preferences. PRACTICAL APPLICATIONS Accurate prediction of acceptance of a product in the marketplace is important. The goal of any test of acceptance is to predict consumer behavior. Therefore, an acceptance test is only valid in terms of how well it predicts the behavior of the consumers in the real world, once they have left the testing situation. It is costly if such tests do not predict this behavior accurately. Accordingly, validation studies should monitor the behavior of the consumers for a requisite amount of time after the test. This has been done for a few studies involving hedonic scales, but there are no published reports for paired preference tests. There is a reluctance to perform such studies because of the time and costs involved. One alternative is to offer consumers the chance to select the products being tested, to take away with them once the test has finished. This might give a clue to “real world” behavior. Since this approach is simple and cost-effective, it is worth investigating.

‘Liking’, ‘Buying’, ‘Choosing’ and ‘Take Away’ preference tests for varying degrees of hedonic disparity

Paired preference tests of liking require consumers to specify which of two foods are preferred or whether there is no preference. For ‘Buying’ preference tests, consumers specify which of two foods they are more likely to buy or whether they might buy either or neither. For ‘Choosing’ preference tests, consumers specify which of two foods they are more likely to choose when offered both, or whether they might choose both or neither. The first test is designed to predict greater degrees of liking, the second to predict buying behavior and the third to predict choice behavior. Yet, test results may not necessarily predict ‘real life’ behavior once consumers have left the testing situation; the ‘test’ preferences may not be ‘operational’. To validate the predictive ability of such tests, consumer behavior should be monitored for several months. Another approach is to allow consumers to take away some of the foods used in the test and observe what they take away. Consumers of potato chips were required to taste chips whose flavor and appearance were obviously different. A first group ( N = 107) were given ‘Liking’, ‘Buying’ and ‘Choosing’ preference tests for two palatable types of chip. After the test, out of sight of the experimenter, consumers were presented with two rows of plain plastic ‘snack’ bags, filled with the chips used in the test. They could take away either two bags of the same type of chip (a ‘Take Away’ preference) or one of each type (no ‘Take Away’ preference) or take neither (rejection). They were also subtly questioned regarding whether they were going to consume the chips themselves or were going to share them with friends. A second group ( N = 103) repeated the experiment. However, for these consumers, one type of chip was unpalatable. In general, ‘Buying’ preferences corresponded more to ‘Take Away’ preferences while ‘Liking’ and ‘Choosing’ preferences showed little correspondence. For the palatable chips, the preferences were spread more evenly than for the case where one type of chip was undesirable. In this latter case, approximately 50% of consumers were consistent over all tests in choosing the palatable chip. This might suggest operational preferences. ‘Take Away’ preferences suggested low predictability for paired preference tests of liking, choosing and buying. ‘Take Away’ preferences are not a substitute for monitoring consumer behavior for several months but they are a step in the right direction.

ASSESSMENT OF PREFERENCE WITH CONTROLS FOR RESPONSE BIAS OPERATING IN THE TEST SITUATION: A PRACTICAL EXAMPLE USING OMEGA-3 ENRICHED WHOLEGRAIN BREADS WITH ECUADORIAN CONSUMERS

Ecuadorian consumers performed paired preference tests between sunflower rye bread and artisan wholegrain bread enriched with omega-3 fatty acids. Preferences for each were split fairly evenly. Further difference tests suggested that these preferences were elicited by visual rather than flavor/texture cues. The preference test included a “placebo” pair of “identical” stimuli to assess statistically whether the responses to the two test stimuli were merely because of response biases operating in the test situation and not differences in their sensory attributes. The concept of an “operational preference” was introduced to understand some of the ambiguities involved in the definition of preference. PRACTICAL APPLICATIONS The measurement of preference and acceptance of foods is important for product development and decisions regarding the launching of new products on to the market. The paired preference test has several problems associated with its design and analysis, and these are worthy of investigation. This article uses a practical example to illustrate some procedures developed as solutions to these challenges. Solutions to the problems involved in preference testing are essential so that the food industry can obtain trustworthy data.

Colour preference of five marine fishes: bias for natural and yellow-dyed krill in laboratory tanks, sea cages and an earthen pond

In this study, the colour preference during feeding was determined in three members of the family Sparidae: girella (Girella punctata Gray), the black porgy (Acanthopagrus schlegeli Bleeker) and the Japanese silver bream (Acanthopagrus latus Houttuyn); and in two members of the family Scombridae: the Japanese horse mackerel (Trachurus japonicus Temminck et Schlegel) and the spotted mackerel (Scomber australasicus Cuvier). The three sparids are omnivorous and are confined to neritic habitats and the two scombrids are schooling planktivores and open-ocean forms. The experiments were conducted under three different holding conditions: grey and white tanks in the laboratory, sea cages and an earthen pond. The prey used in the tests was the Antarctic krill, in its natural colour (control) and in artificial colours of yellow, red, green, blue (produced with food dyes) and black (Chinese ink). These prey were offered in different two-colour pairs to groups of fish, and the colour of the krill attacked first was recorded. The frequencies of first attacks against each colour of the different pairs were analysed by the paired-preference test and Thurstone's law of comparative judgment. The data were converted into mean z-scores and significant biases from zero were noted. The five species took without hesitation all the krill of all colours, but preferred blue krill the least, and did not clearly distinguish red from black. The three sparids showed a strong bias for yellow krill under all holding conditions. The two scombrids preferred natural krill and showed poor colour preference. The observed colour preference was probably due to colour per se and may be an innate ability, rather than due to relative brightness (sensitivity of the fish eye), prey conspicuousness (pigmented eyes of the krill), or the associated taste of the dyes.

Consumer acceptance of fresh blueberries in bio-based packages

Instrumental analyses have shown that non-vented bio-based containers made from poly(lactic acid) (PLA) have the capability to enhance blueberry shelf life as compared with commercial vented petroleum-based clamshell containers. However, consumer preference has not been explored so far. In this study, two sensory evaluations, triangle and paired preference tests, were performed after storing fruit in both containers at 3 and 10 degrees C for 7 and 14 days. In addition, physicochemical analyses were performed after each tasting in order to correlate instrumental findings with consumer preference. The results of the triangle test showed the capability of the consumer to differentiate (P < or = 0.001) between blueberries from different packages at both storage temperatures. A consumer preference for flavour, texture, external appearance and overall quality (P < or = 0.001) of blueberries packaged in PLA containers was observed in the paired comparison test. The instrumental analyses showed that blueberries in the PLA packages exhibited a weight loss below the limit for marketable life, a stable soluble solid content and titratable acidity and no fungal growth during storage. Consumers distinguished between blueberries from different packages and preferred those packaged in the PLA containers. The instrumental analyses showed that the usable life of the berries was extended in the PLA containers. A correlation between consumer preference and instrumental evaluations was found.

Neural markers of subordinate‐level categorization in 6‐ to 7‐month‐old infants

Subordinate-level category-learning processes in infants were investigated with ERP and looking-time measures. ERPs were recorded while 6- to 7-month-olds were presented with Saint Bernard images during familiarization, followed by novel Saint Bernards interspersed with Beagles during test. In addition, infant looking times were measured during a paired-preference test (novel Saint Bernard vs. novel Beagle) conducted at the conclusion of ERP recording. Slow wave activity corresponded with learning a familiarized category at the subordinate and basic levels, whereas Negative central (Nc) and P400 components were linked with novel category preference. The results provide the first evidence identifying the neural markers of subordinate-level categorization observed in looking-time tasks conducted with infants. Moreover, when considered in conjunction with prior research investigating the neural markers of basic-level categorization in infants, the findings indicate that (1) slow wave and Nc components of infant ERP waveforms are general markers for processes of category learning on the one hand and novel category preference on the other, (2) novel category preference for a contrast category at the basic and subordinate levels have the Nc component in common, but novel category preference at the subordinate level is accompanied by an additional P400 component, a finding in keeping with the notion that subordinate-level categorization is governed by mechanisms supplementary to those underlying basic-level categorization, and (3) slow wave activity associated with subordinate-level learning followed that associated with basic-level learning by approximately 200 ms, a result in accord with a coarse-to-fine scheme for the emergence of category partitioning.

Paired preference tests: ‘Liking’, ‘Buying’ and ‘Take Away’ preferences

Paired preference tests of liking require consumers to specify which of two foods are preferred or whether there is no preference. For ‘Buying’ preference tests, consumers specify which of two foods they are more likely to buy or whether there is no operational difference in likelihood to buy. The former test is designed to predict choice behaviour, the latter, buying behaviour. To validate the predictive ability of such tests, consumer choice and buying behaviour should be observed for several months. Another approach is to allow consumers to take away some of the foods used in the test and observe what they take. Consumers of potato chips were required to taste chips whose flavour and appearance were obviously different. A first group ( N = 109) were given a traditional paired preference test of liking. A second group ( N = 108) were given a preference test of buying. A third group ( N = 101) were given both tests. After the test, out of sight of the experimenter, consumers were presented with two rows of plain plastic ‘snack’ bags, filled with the chips used in the test. They could take away either two bags of the same type of chip (a ‘Take Away’ preference) or one of each type (no ‘Take Away’ preference) or take neither (rejection). ‘Liking’ preferences predicted what was taken away for only 48% of consumers for the first group and 45% (third group). For ‘Buying’ preferences, the correspondence was 56% (second group) and 60% (third group). Using buying tests separately or together with liking produced some differences. More reliably, approximately 60% of consumers in all groups chose one bag of each. ‘Take Away’ preferences suggested low predictability for paired preference tests of liking and buying. ‘Take Away’ preferences are not a substitute for following a consumer for several months but they are a step in the right direction.

Preference for full-fat over low-fat foods among individuals suffering from coronary heart disease and healthy controls

Dietary behaviour can modify the risks for coronary heart disease (CHD). Dietary fat contributes to the sensory characteristics of many foods, but there are individual differences in liking for regular and reduced fat products. Preference for dietary fat might differ between healthy individuals and those of diagnosed CHD status. Preference for full-fat versus low-fat foods was assessed in a group suffering from CHD ( N = 24) and a healthy control group ( N = 41). Preferences were evaluated using a series of paired preference tests including 34 food pairs. Further, patterns across fat preference and a range of known risk factors for CHD were examined. The study was conducted in Sweden; March 2004 until May 2006. Overall the full-fat food items were preferred to the low-fat alternatives by both patients and control participants. The pattern of preference responses diverged significantly between patients and controls on only four of the 34 food items, in both directions, why preference related to total fat content per se is not confirmed as differentiating significantly between a group diagnosed with CHD compared to a healthy control group.

USE OF PURCHASE PREFERENCE OPTIONS TO INCREASE “NO PREFERENCE” FREQUENCIES IN PLACEBO PREFERENCE TESTS

ABSTRACT Besides responses to the different stimuli being tested in a paired preference test, responses to identical “placebo” stimuli can be used as a screening tool to identify biased consumers. Those consumers who give preference responses to identical stimuli can be assumed to be biased. Accordingly, only the data from unbiased consumers need to be considered for the different stimuli. The problem with this procedure is that the sample size is reduced. The goal of the present research was to see whether using options associated with purchase intent, elicited a greater number of “No Preference” responses to identical “placebo” stimuli. It was found that they did. The increase was large when the preference options implied exclusivity. In conditions where the preference strength options were not so strong, the frequency of “No Preference” responses dropped accordingly. PRACTICAL APPLICATIONSA problem with paired preference testing is the tendency of consumers to give false preferences, which produces the seriously misleading overestimation of the proportion of consumers who have preferences for one or other of the products being assessed. The “placebo” condition is an important control for alleviating this problem. The statistical analysis can be improved by finding a protocol that maximizes the proportion of “No Preference” responses in the placebo condition. The key finding here is that using purchase intent questions rather than preference questions may possibly provide a way of achieving this aim.

OPTIMIZATION OF THE SENSORY ACCEPTABILITY OF A REDUCED SALT MODEL READY MEAL

ABSTRACT The aim of this study was to examine the effect of salt levels on the sensory acceptability of a model frozen chicken curry ready meal. A sample product with typical commercial salt levels (0.6%, control) and a low‐salt chicken curry ready meal (0.2%) were prepared using a recipe supplied by an industrial partner. Salt was then added to the low‐salt meal at levels ranging from 0 to 1.3%, giving a range of meals with final salt concentrations between 0.2 and 1.5%. Sensory trials incorporating paired comparison, triangle, preference and ranking tests indicated that salt levels in a chicken curry ready meal could be reduced to a level of 0.4% without detecting a difference in saltiness when compared to a typical commercial added salt level of 0.6%. Results indicated that the sensory threshold level for salt in this meal was 0.2%. Incorporation of a number of different commercial salt substitutes allowed a further reduction in salt levels of 0.2% and to a final concentration of 0.2% without panelists detecting a noticeable difference in saltiness. PRACTICAL APPLICATIONSHigh dietary salt intake is now recognized as an important casual factor in the rise in blood pressure with age in industrialized countries such as Ireland. Irish consumers are increasingly purchasing ready meals because of lifestyle demands leaving less time available to prepare meals from fresh ingredients. Health agencies throughout the world are growing increasingly concerned with the high intake of nondiscretionary sodium from salt and sodium containing additives used in these meals. The Food Safety Authority of Ireland (FSAI) has set a long‐term goal to reduce the average population intake of salt from 10 to 6 g a day by 2010 through a partnership approach with the food industry (FSAI). This project aims to produce a low‐salt chicken curry ready meal that will aid the FSAI in achieving this national health strategy goal and provide technical data on reformulation strategies and sensory properties for ready‐meal producers.

PAIRED PREFERENCE TESTS: “50:50” AND “ALTERNATING” NO PREFERENCES

ABSTRACT Because the concept of “No Preference” is ambiguous, two types of “No Preference” are defined: a “50:50” No Preference, defined operationally as consumers presented with both products having a 50% chance of choosing either, and an “Alternating” No Preference, where the probability is not 50%. The consumer would be more likely to choose one of the products. However, later, he or she might choose the other product. To investigate this, paired preference tests were performed with and without the “No Preference” option for various products. No discernible trend was noted for consumers who had chosen the “No Preference” option and distributed their votes among the preference options. These consumers and those who changed their preferences were classified according to the “50:50” No Preference and “Alternating” No Preference dichotomy accordingly. PRACTICAL APPLICATIONSBesides the tendency of consumers to report false preferences, paired preference tests have another problem: the concept of “No Preference” is ambiguous. It could mean that consumers liked both products equally and so would always have a 50% chance of choosing either. It could also mean that the probability is not 50% on any one occasion but varies so that one product is chosen on one occasion and the other product on another occasion. To avoid confusing the consumer so as to obtain more valid data, it is important to specify these two meanings of “No Preference.” This study is a first step in that direction and should help consumers understand better the instructions for preference tests.

Exploiting flavour preferences of common marmosets to increase palatability of a dry pellet diet

Although commercially available complete diets exist for common marmosets, the animals’ consumption of these diets (available in dry pellet form) is typically very low. Increasing consumption of the pellet diet could have positive consequences for the welfare of the marmosets as the pellets are designed specifically to meet their full nutritional requirements, and therefore an increase in intake should help to ensure that they take in an appropriate balance of nutrients. We carried out a series of studies targeted towards improving the palatability, and hence increasing the intake, of a complete dry pellet diet for marmosets. In Study 1 we attempted to determine which of a wide range of flavours appeared to be preferred by the marmosets. In Study 2 we tested the marmosets’ preferences for a smaller number of highly preferred flavours (as determined in Study 1) when actually added to the dry pellet diet in a series of paired preference tests. Finally, in Study 3 we tested whether adding the most highly preferred flavours (as determined in Study 2) to the dry pellet diet would in fact increase consumption of these pellets in comparison with unflavoured pellets. Despite finding strong and consistent preferences for particular flavours amongst the marmosets, we found that adding these to the pellets did not significantly increase consumption. Reasons for this are discussed, along with other potential modifications which might prove more successful in increasing consumption of pellet diets for marmosets.

PAIRED PREFERENCE “PLACEBO” TESTS WITH “IDENTICAL” STIMULI: DOES INTRODUCING GRADED PREFERENCE RESPONSES AFFECT THE FREQUENCY OF “NO PREFERENCE” RESPONSES?

ABSTRACT In the “placebo” control condition for paired preference testing, “identical” stimuli are presented to consumers to determine the frequency of preference and “no preference” responses induced by the hidden demand characteristics of the testing condition. As a control for bias, induced by such hidden demand characteristics, these frequencies can be compared with the actual preference frequencies of the nonidentical test stimuli to be assessed for preference. It was hypothesized that the introduction of graded preference response options might reduce the frequency of “no preference” responses in the placebo condition. Using identical yogurt stimuli with related‐sample (single‐group) and independent‐sample (multigroup) designs, this hypothesis was not confirmed. PRACTICAL APPLICATIONSThe “placebo” condition in paired preference testing provides a way to control the tendency of consumers to give false preference. The statistical analysis can be improved by finding a protocol that maximizes the proportion of “no preference” responses in the placebo condition. This can be done by increasing the number of response options that imply no preference. Yet, there is sometimes a desire to increase the number of preference options by using graded responses for preference strength. Does this alter the dynamics of the ever‐important placebo condition by reducing the number of “no preference” responses? This project found that any effect was minimal.

PAIRED PREFERENCE TESTS USING PLACEBO PAIRS AND DIFFERENT RESPONSE OPTIONS FOR CHIPS, ORANGE JUICES AND COOKIES

ABSTRACT Preference tests were performed for varieties of potato chips, orange juices and chocolate chip cookies using three response protocols: the traditional paired preference test with the “no preference” option, a 9‐point hedonic scale and a 6‐point hybrid hedonic/purchase intent scale. The different stimuli to be assessed were presented in pairs, but putatively identical stimuli were also presented as a “placebo” pair. Performance on the placebo pair with identical stimuli provided a measure of the hidden demand characteristics of the test protocol. The presentation of the different pairs provided a measure of preference accompanied by such hidden demand effects. Comparison between the two allowed a better measure of preference per se. The order of presentation of the identical and different pairs did show occasional slight evidence of contrast effects. For the placebo “identical” pairs, a majority of consumers reported false preferences. Liking questions with the hedonic and hybrid scales elicited fewer false preferences than preference questions with the paired preference protocol. Yet, the effects tended to be slight. The 6‐point hedonic/purchase intent scale exhibited the fewest false preferences in the placebo condition, and this was because of its fewer categories rather than any cognitive strategy change elicited by its different labels.PRACTICAL APPLICATIONSA problem with paired preference testing is the tendency of consumers to give false preferences, which produces the seriously misleadingoverestimation of the proportion of consumers who have preferences for one or other of the products being assessed. The placebo condition is an important control for alleviating this problem. The statistical analysis can be improved by finding a protocol that maximizes the proportion of “no preference” responses in the placebo condition. The key finding here is that using hedonic or purchase intent questions rather than preference questions may possibly provide a way of achieving this aim.