Domains of disgust sensitivity: revisited factor structure of the questionnaire for the assessment of disgust sensitivity (QADS) in a cross-sectional, representative german survey

Disgust sensitivity describes an individual's time-invariant, genetically-based personality trait, a predisposition to reacting to specific materials with disgust [[1], p.111; [2]]. The specific materials that trigger disgust can be grouped into five theoretically proposed categories of disgust elicitors [3]: badly tasting substances can produce Distaste, which protects the body from poisons. Core Disgust can be provoked by rotten food, body products, rodents, and other small vermin in order to protect the body from disease or infection. Animal Nature/Reminder Disgust refers to sex, death, poor hygiene, and body envelope violations for protection against death and mortality. Interpersonal-Contamination Disgust protects the body by limiting the contact with strangers and other undesirables. Moral Disgust mainly protects the social order in case of moral offenses such as rape or murder.

Based on the 32 items of the original Disgust Scale (DS) by Haidt, McCauley, and Rozin [4] only three of the eight DS factors were found to be psychometrically stable. These three stable factors are Core Disgust, Animal Reminder Disgust, and Contamination Disgust with 25 items overall which represent the Disgust Scale - Revised (DS-R) by Olatunji and colleagues [5]. The reliabilities of the DS-R scales varied from (Cronbach's Alpha) .71 to .82.

Schienle, Walter, Stark, and Vaitl [1] translated all the items from the original DS into German and implemented a consistent five-point rating scale. Unfortunately, the translation led to insufficient psychometric properties. Therefore, 28 newly generated expert-rated items - four items for each of the existing DS scales and four items for a new scale called Deformation - were included. In a second step, any item of the translated and extended DS whose Measurement of Sampling Adequacy came to > .70, was excluded. In a third step, the factor structure was tested.

The parallel analysis and an obliquely rotated Principal Axis factor analysis revealed five factors: Death/Deformation, Body Secretions, Spoilage, Poor Hygiene, and Oral Rejection. In order to adjust the unsatisfactory internal consistency of .66 of Poor Hygiene, four more items were generated. The following confirmatory factor analysis of the 39-item-version revealed a Root Mean Square Error of Approximation (RMSEA) of .06 which suggests a sufficient model fit. Two more items were excluded as their factor loadings were < .30. The final German instrument "Fragebogen zur Ekelempfindlichkeit" will be referred to as "Questionnaire for the Assessment of Disgust Sensitivity" (QADS) in the remainder of this article and can be found as Additional file 1. Even though modest to good reliabilities were reported for all the scales (.69 to .85), the calculations of the final version were based on a small non-representative sample of N = 220 participants.

The discrepancies in the factor structures of the QADS and the DS/DS-R as well as the following shortcomings led to the necessity of revisiting and possibly refining the QADS factor structure.

Most of the studies on the DS factor structure applied estimation methods that did not take into account the non-normality of item distributions [5]. The exact estimation method of the QADS' confirmatory factor analysis had not been reported by Schienle et al. [1], therefore, the validity of that factor structure is questionable at best. Furthermore, the QADS factor structure was calculated based on a small, non-representative sample and had not yet been replicated. From a theoretical point of view, the scales do not clearly represent or directly refer to the groups of disgust sensitivity elicitors as proposed by Rozin, Haidt, and McCauley [3].

Consequently, the first aim of this study was to find and confirm a new, statistically coherent, data-driven and theoretically sound factor structure on a large representative German sample while applying adequate estimation methods. The second aim was to compare the fit of this structure to the fit of alternative structures in the present sample. Third, the standard percentages will be accounted for.

The present study aims at analyzing the factor structure of the Questionnaire for the Assessment of Disgust Sensitivity (QADS), a generalized self-report instrument that assesses the individual disposition of 'disgust sensitivity'. For the first time, this analysis was based on a large representative sample.

The adjustment of the statistical procedures during the exploratory and confirmatory factor analyses to the non-normality of item distributions led to a model with three statistically coherent, data-driven, theoretically sound, and highly correlated factors. This model moderately fits the presented data from a representative German sample, and fits better than an unrestricted one-factor model or the five-factor model proposed by Schienle and colleagues [1].

Factor one of the preferred three-factor model assembles 15 items: all but one Oral Rejection item, five items of Body Secretions, three Spoilage items and two of Poor Hygiene. The idea behind this factor can be considered as Core Disgust according to Rozin and colleagues [3], i.e. disgust triggered by the threat of disease through mostly oral contact and a sense of offensiveness, including stimuli such as rotten food and body secretions.

Factor two consists of nine items: all the Death/Deformation items as well as two Spoilage items that overlap with Death as they point to dead creatures. This factor clearly reminds people of their animal origin and mortal nature as Animal Reminder Disgust suggests [3].

Factor three incorporates 13 items: seven Poor Hygiene items, three Spoilage items, two Body Secretions items and one Oral Rejection item. The major concept behind this factor can be referred to as Contamination Disgust, representing reactions toward the perceived threat of contagion through mainly non-oral contact, i.e. inhalation or skin contact (see [3, 5] p.285).

It can be assumed that the three identified factors overlap mainly in content with the three factors of the Disgust Scale - Revised (DS-R) [5]. Although 15 QADS items (items 8, 10 to 15, 27 to 33, 35, 36) are also included in the 25 DS-R items, the QADS is more than a mere German DS translation. It contains several items that strongly contribute to the respective factor but are not included in the original DS, e.g. items 3, 13, 16, 19, 23, and 34. Future research could investigate a combined item pool of both the DS-R and the QADS while examining the convergent validity of these measurement instruments.

Item-scale-correlations were medium to high, replicating the findings by Olatunji and colleagues [5]. The QADS factors inherited very good reliabilities of .90 to .95, which were slightly higher than those reported by Schienle and colleagues [1] for the five original QADS factors (.69 to .85). They were also higher than those presented for the DS and DS-R with a reliability of .84 [4] and an internal consistency of < .70 [5], respectively. This might have been due to diverse item scaling in the DS and its revised version or too few items per factor in the original QADS.

The QADS factors were demonstrated as unaffected by the age of the participants. This might be due to the probably time-stable nature of the trait-like concept. Gender influences, however, were found. Women were moderately more sensitive to disgust than men. Similar gender effects were reported earlier [4, 17] and are of importance as they mediate gender differences in disgust-related disorders, e.g. contamination fear in individuals with an obsessive compulsive disorder [18].

Construct validity on a conceptual level should be given as the items were partly derived from established disgust sensitivity measures, i.e. the DS and the DS-R. Construct validity on a factorial level is supported by recent findings by Olatunji and colleagues [19]. Convergent validity was also tested by van Overveld and colleagues ([20], see also [5]) using the Disgust Propensity and Sensitivity Scale by Cavanagh and Davey [21]. A comparison of QADS and DS-R to this or other generalized disgust instruments such as Wronska's questionnaire [22] and the Disgust Emotion Scale by Kleinknecht and colleagues [23] still need to be carried out in large representative samples and with adequate statistical methods adjusted to possibly non-normal item distributions.

Another aspect is that the concept of disgust sensitivity might need to be refined since some of the popular definitions rely on the empirical basis of now revised findings. The DS-R, for example, explicitly relies on the theoretical concepts by Rozin and colleagues [3] instead of several more or less independent domains as the DS did. The underlying three-factor model of disgust sensitivity is further supported by recent findings as all three factors were demonstrated to be distinct in relation to personality characteristics, behavioral, and physiological reactions as well as clinical fears [19]. Olatunji and colleagues [19] speak of "kinds of disgusts" while referring to what we call "disgust sensitivity", hereby not precisely distinguishing between the emotion of disgust and the underlying trait-like preparedness to experience disgust, Van Overveld and colleagues [20] postulate an even more sophisticated view on disgust sensitivity. They argue that the concept itself should be renamed disgust propensity, i.e. how easily a person becomes disgusted in opposition to the tendency of experiencing something as 'horrid', or rather how strongly a person is bothered by it, which they call disgust sensitivity. It seems important to note that the QADS factors are named according to the disgust sensitivity concept by Rozin and colleagues [3] since both the QADS items and DS-R items have not yet been divided into propensity items and sensitivity items.

Developed as a paper-and-pencil test with as few as 37 five-point scaled items, the QADS can be applied easily and quickly. In sum, the QADS is age-independent, objective, reliable, and now standardized on a representative sample with tabulated standard percentages for both genders. On account of its advantageous design being comprised of three different factors, it can be used to assess specific disgust domains as well as dispositional disgust sensitivity via the Main Score. Limitations are due to unexplored overlaps with other disgust sensitivity measures, their items, and factor structures. To be specific, a comparison of the QADS, DS-R and other generalized disgust sensitivity instruments still needs to be conducted. For theoretical reasons, including "moral disgust" items could be considered [3].