'Validation of the German version of SPOVI and EMETQ-13'
(AsPredicted #114541)
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1) Have any data been collected for this study already?
No, no data have been collected for this study yet.

2) What's the main question being asked or hypothesis being tested in this study?
A multistep translation and subsequent psychometrical validation of two self-report instruments for emetophobia; the Specific Phobia of Vomiting Inventory (SPOVI; Veale et al., 2013) and the Emetophobia Questionnaire (EMETQ-13; Boschen et al., 2013) via a cross-sectional online survey in (A) an adult community sample as well as (B) in psychotherapy outpatients. Furthermore, we want to estimate the frequency of clinically-relevant symptoms of emetophobia in these mixed samples.
Project website (German): https://klipsy.uni-mainz.de/forschung/diadem/

3) Describe the key dependent variable(s) specifying how they will be measured.
(A) Questionnaires used in the community sample (all in German versions):

(1) Specific Phobia of Vomiting Inventory (SPOVI; Veale et al., 2013)
(2) Emetophobia Questionnaire (EMETQ-13; Boschen et al., 2013)
(3) Dimensional Obsessive-Compulsive Scale Short Form (DOCS-SF; Kühne et al., 2021)
(4) Eating Disorder Examination-Questionnaire 8 (EDE-Q-8; Hilbert & Tuschen-Caffier, 2006)
(5) Modified Short Health Anxiety Inventory (MSHAI; Bailer & Witthöft, 2014)
(6) Mini – Social Phobia Inventory (MiniSPIN; Wiltink et al., 2017)
(7) Patient Health Questionnaire-4 (PHQ-4; Löwe et al., 2010)
(8) Skala zur Erfassung der Ekelsensitivität [Assessment of disgust sensitivity] (SEE; Schienle, et al., 2010)
(9) Somatosensory Amplification Scale (SSAS; Doering et al., 2015)
(10) Work & Social Adjustment Scale (Mundt et al., 2002)

(B) In the psychotherapy outpatient sample, the Specific Phobia of Vomiting Inventory (SPOVI; Veale et al., 2013) will be the main questionnaire and other routine data (e.g., demographic, clinical characteristics) will be extracted if available.

4) How many and which conditions will participants be assigned to?
The research project does not include any experimental conditions (cross-sectional survey).

5) Specify exactly which analyses you will conduct to examine the main question/hypothesis.
Our main focus is on psychometrically validating the SPOVI and EMETQ-13 in a German community sample. Participants will be recruited online (e.g., through social media, newsletter, and self-help forums) over a three-month period. We will investigate convergent and discriminant validity with other questionnaires, using correlational analysis. We will also assess the internal consistency (McDonald's Omega, ω) of the scales and inspect item characteristics. Floor effects will be examined using distributions on item/sum score level. The factorial structure of the questionnaires will be tested using CFA. For the SPOVI, two models will be tested based on previous literature: the originally proposed two-factor model (Veale et al., 2013), and a second, one-factor model (Maack et al, 2018). For the EMETQ-13, we will test the originally proposed 3-factor model (Boschen et al., 2013). Absolute (e.g., RMSEA), comparative (e.g., CFI), and predictive (e.g., AIC) fit indices will be analyzed. Modification indices will be calculated to identify where linear constraints might be relaxed to improve model fit. The chi‐square (χ2) difference test will be performed for nested models.
Secondly, we will investigate the prevalence of possible emetophobia both in the community and in a psychotherapy outpatient clinic sample using the proposed cutoffs of both instruments (SPOVI > 10, Veale et al., 2013; EMETQ-13 > 22, Boschen et al., 2013). In the psychotherapy outpatient sample, we will be able to determine the comorbidity of possible emetophobia with further mental disorders (e.g., depression, anxiety) or its association with various dimensions of psychopathology.

6) Describe exactly how outliers will be defined and handled, and your precise rule(s) for excluding observations.
Inclusion criteria: participants who provide informed consent and are ≥ 18 yrs will be included in the survey.
(A) Online-survey in community sample: participants with an excessively fast completion time in the SPOVI and EMETQ-13 (relative speed index > 2, Leiner et al., 2019) and the wrong answer to an instructed response item will be used as post-hoc exclusion criteria.

7) How many observations will be collected or what will determine sample size?
No need to justify decision, but be precise about exactly how the number will be determined.
(A) Sample size recommendations for conducting CFA include rules of thumb such as a minimum of 10 cases per estimated parameter (Nunnally & Bernstein, 1967; Jackson, 2003) or stem from simulation studies, e.g., ≥ 200 - 500 when applying a robust estimation method such as WLSM (Forero, Maydeu-Olivares, & Gallardo-Pujol; 2009). Based on these, the planned sample size for the community sample is N = 300 within a three-months recruitment period.

(B) The psychotherapy outpatient sample will presumably be recruited at two sites over approximately 6 months (or until the sample size below is reached). The patient cases per month determine the sample size (around 40-60 per site), which results in a planned sample size of a minimum of N = 200 participants.

8) Anything else you would like to pre-register?
(e.g., secondary analyses, variables collected for exploratory purposes, unusual analyses planned?)
Exploratory variables: Demographics (age, gender, relationship/marital status, education, occupation) body mass index (BMI), self-constructed emetophobia items (e.g., time since the last vomiting, medication intake for nausea/vomiting, duration of emetophobia, most feared aspect of vomiting, intrusive thoughts).

Exploratory Factor Analysis (EFA) with SPOVI/EMETQ-13.

Measurement invariance across gender of SPOVI/EMETQ-13 (multi‐group CFA).

Subgroup analyses: adult convenience sample vs. psychotherapy outpatients vs. participants with headache diagnosis (e.g., tension-type headache, migraine, cluster headache, medication overuse headaches).