Comparación de dos métodos para corregir el sesgo de no respuesta a una encuesta: sustitución muestral y ajuste según propensión a responder

Public Opinion on Food Policies to Combat Obesity in Spain

(1) Introduction: Poor diet is the fourth-leading cause of mortality in Spain, where adherence to the Mediterranean diet has declined in recent decades. To remedy this situation, a series of food policies have been proposed that would be easier to implement if they had public support. (2) Material and methods: Cross-sectional study covering a representative sample of the Spanish population (n = 1002), using telephone interviews that addressed nine food policies under four headings, namely, advertising, labeling, composition, and provision and sale. The sociodemographic determinants of support for these policies were analyzed using the chi-squared (χ2) test and Poisson multiple regression models with robust variance. (3) Results: All the proposed measures received more than 60% support. The policies that received greatest support were those targeting labeling at 96.6%, while the policies that received the least support were those directed at banning free refills at restaurants, at 63%. Support for policies was higher among women, older adults, and persons professing left-wing ideological affiliations. Compared with men, women's support for advertising policies was 21% higher: similarly, compared with the youngest age group (18-29 years), support by the over-65 segment for provision and sale policies was 52% higher. Support for composition policies was 28% lower among persons with right-wing as opposed to left-wing political sympathies. (4) Conclusions: The authorities enjoy the support of the Spanish public as regards implementing food policies proposed by experts and overcoming the resistance of sectors opposed to such measures.

Public Support for the Imposition of a Tax on Sugar-Sweetened Beverages and the Determinants of Such Support in Spain

(1) Background: Taxes on sugar-sweetened beverages are an effective public health intervention, but can be difficult to implement in the absence of public support. This is the first study to analyze the Spanish population’s support for a tax on sugar-sweetened beverages. (2) Methods: We conducted a cross-sectional study of a representative sample of the Spanish adult population (n = 1002), using a computer-aided telephone interview with a questionnaire on nutritional policies. The support for the tax was calculated by the percentage of those who agreed plus those who strongly agreed with the measure. The sociodemographic determinants of support for the tax were analyzed using chi-squared test (χ2) and Poisson multiple regression models with robust variance. (3) Results: Of the participants, 66.9% supported a tax on sugar-sweetened beverages. Support for the tax was 9.2% higher (70% vs. 64.1%) when responders were first asked about support for tax relief and subsidies for healthy foods (p = 0.049). Support for the tax was 16% and 35% lower among persons reporting center and right-wing political sympathies (p < 0.01), and 16% lower among regular consumers of sugar-sweetened beverages (p = 0.01). (4) Conclusions: A clear majority of the Spanish population is in favor of imposing a tax on sugar-sweetened beverages. Awareness-raising campaigns and a policy of combining the measure with subsidies or tax cuts on healthy foods could increase the level of support among those currently against the intervention.

[Analysis of selection bias in the pilot study of a longitudinal study on aging in Spain]

OBJECTIVES

To demonstrate that selection of a probabilistic sample at a national level for a study of aging in Spain is subject to selection bias. To quantify the losses produced after each phase of the administration of a questionnaire.

METHODS

We performed a cross-sectional study of the Spanish community-dwelling population aged 50 years or older between 2010 and 2011. Through multivariate logistic regressions, the characteristics of the census tract of the patients' residence were compared between those who agreed (n = 5,813) or refused (n = 7,023) to be included in the sampling frame and between those who agreed (n = 1,677) or refused (n = 2,875) to participate in the study. The individual characteristics of persons who responded (n = 1,398) or refused to respond (n = 346) to a face-to-face questionnaire administered after a telephone interview were also compared. In addition, the reasons for refusal were studied.

RESULTS

The most frequent specific reasons for refusing to be included in the sampling frame or to participate in the study were poor health and disability (14.4% and 27.9%, respectively). In both cases, refusal was more frequent in the census tracts of districts with a lower socioeconomic level or those located in Catalonia, Guipúzcoa or Biscay. Individuals older than 81 participated less frequently in the face-to-face questionnaire. Between 8.6% and 18.4% of participants were lost at each stage of information retrieval.

CONCLUSION

Probabilistic sampling in sampling points chosen by the researchers would allow more resources to be devoted to increasing response rates among the groups who are less likely to participate. Questions should be concentrated in only one shorter questionnaire, administered before blood extraction.

Monte Carlo simulation of the cost-effectiveness of sample size maintenance programs revealed the need to consider substitution sampling

OBJECTIVE

To assess the cost-effectiveness of sample size maintenance programs in a prospective cohort.

STUDY DESIGN AND SETTING

The Living with Diabetes Study in Queensland, Australia is a longitudinal survey providing a comprehensive examination of health care utilization and disease progression among people with diabetes. Data from this study were used to compare the cost-effectiveness of a program incorporating substitution sampling with two alternative programs: "no follow-up" and "usual practice."

RESULTS

A program involving substitution sampling was shown to be the most effective with an additional 3,556 complete responses (compared with a "no follow-up" program) and an additional 2,099 complete responses (compared with "usual practice"). An incremental analysis through a Monte Carlo simulation found substitution sampling to be the most cost-effective option for maintaining sample size with an incremental cost-effective ratio of $54.87 (95% uncertainty interval $52.68-$57.25) compared with $87.58 ($77.89-$100.09) for "usual practice."

CONCLUSIONS

Based on the available data, a program involving substitution sampling is economically justified and should be considered in any approach with the aim of maintaining sample size. There is, however, a continuing need to evaluate the effectiveness of this option on other outcome measures, such as bias.

Avoidance and inhibition do not predict nonrespondent bias among patients with inflammatory bowel disease

Background

It has been suggested that participant withdrawal from studies can bias estimates. However, this is only possible when withdrawers and nonwithdrawers differ in an important way. We tested the hypothesis that withdrawers are more likely than nonwithdrawers to be avoidant and negatively affected.

Methods

A total of 1160 participants with inflammatory bowel disease were recruited at different sites in Switzerland. Their levels of avoidance coping and negative affectivity were rated by means of 2 short baseline questionnaires. One year later, they were sent a longer follow-up questionnaire. The primary outcome was return versus non-return of the follow-up questionnaire within 3 months. After controlling for potential confounders identified in an extensive literature search, we estimated the odds of returning the follow-up questionnaire for 1 standard deviation of avoidance coping and negative affectivity.

Results

The odds ratio for 1 standard deviation was 1.03 (95% confidence interval: 0.89–1.18) for avoidance coping and 1.02 (0.89–1.17) for negative affectivity.

Conclusions

The odds of returning the questionnaires did not depend on avoidance coping or negative affectivity.