Short and sweet: Comparing strategies for the reduction of questionnaires on self-criticism and social safeness while preserving construct validity.

Measuring psychological traits with standardised questionnaires is an essential component of clinical practice and research; however, patients and participants risk fatigue from overly long and repetitive measures. When developing the short form of a questionnaire, the most widely used method for selecting an item subset uses factor analysis loadings to identify the items most closely related to the psychological construct being measured. However, this approach will tend to select highly correlated, homogeneous items and might therefore restrict the breadth of the construct examined. In this study, we will present Yarkoni's genetic algorithm for scale reduction and compare it with the classical scale reduction method. The algorithm will be applied to the shortening of three instruments for measuring self-compassion and social safeness (two unidimensional measures and a three-factor measure). We evaluated the shortened scales using correlation with long-form scores, internal reliability and the change in the correlations observed with other related constructs. Findings suggested that the classical method preserves internal reliability, but Yarkoni's genetic algorithm better maintained correlations with other constructs. An additional qualitative assessment of item content showed that the latter method led to a more heterogeneous selection of items, better preserving the full complexity of the constructs being measured.

The roles of autonomous motivation and self-control lapses in concurrent adherence to a gluten-free diet and a self-chosen weight loss plan in adults with coeliac disease.

Objective: Examine the correspondence between autonomous motivation, self-control lapses, and adherence, to a gluten-free diet (GFD) and weight loss plan in adults with coeliac disease; and assess the impact of the interaction of motivation style and self-control lapses on adherence to both diets. Design: Cross-sectional survey in 519 adults with coeliac disease, 238 of whom were also attempting weight loss. Main outcome measures: Adherence, motivation style, frequency of temptation and self-control lapses (e.g. when tired, stressed, happy) for GFD and weight loss plan. Results: Autonomous motivation was higher, and amotivation lower, for the GFD than weight loss; adherence to the two diets was unrelated. Similar circumstances led to temptation and self-control lapses across diets; both were less frequent for the GFD than weight loss. Motivation and self-control lapses explained 21% and 35% of the variance in adherence, respectively; the interaction between motivation and lapse frequency did not explain additional variance for either diet. Conclusions: There are clear benefits to developing autonomous motivations and strategies to resist temptation for both the GFD and weight loss. Understanding how these processes differ and interact across diets may lead to the design of interventions to improve adherence and weight outcomes in coeliac disease.