A randomized trial about the perceived informativeness of new empirical evidence Does beta-carotene prevent (cervical) cancer?

The perceived informativeness of a publication can be assessed by measuring the change in belief it induces among the scientific public, regarding a certain hypothesis. In a randomized trial, we studied the effect of empirical evidence from a clinical experiment and a case-control study on the hypothesis that beta-carotene protects against (cervical) cancer. The study population consisted of first authors of recently published patient-oriented research papers. They received an abstract of the clinical experiment, of the case-control study, or a "placebo" abstract. The latter was used to assess the specific effect of the empirical evidence in the two real studies. The change in belief in the hypotheses was expressed as a likelihood ratio (LR). All three abstracts led to a decrease in belief in the hypothesis. The median LRs of the abstracts of the experiement, case-control study and "placebo" were 0.33, 0.45, 0.75 respectively. This paper shows that the belief in a certain hypothesis is influenced by the quality of empirical evidence in a study. The magnitude of change induced by the experimental and case-control abstract had the anticipated order, but the change in belief induced by the "placebo" abstract was larger than we had expected. Reasons for this may be the concise information in the abstract and the variable methodological training of the study population

The Relationship Between Methodological Quality and Conclusions in Reviews of Spinal Manipulation

To study the relationship between the methodological quality and other characteristics of reviews of spinal manipulation for low back pain on the one hand and the reviewers’ conclusions on the effectiveness of manipulation on the other hand. Reviews identified by MEDLINE search, citation tracking, library search, and correspondence with experts. English- or Dutch-language reviews published up to 1993 dealing with spinal manipulation for low back pain that include at least two randomized clinical trials (RCTs). Methodological quality was assessed using a standardized criteria list applied independently by two assessors (range, 0% to 100%). Other extracted characteristics were the comprehensiveness of the search, selective citation of studies, language, inclusion of non-RCTs, type of publication, reviewers’ professional backgrounds, and publication in a spinal manipulation journal or book. The reviewers’ conclusions were classified as negative, neutral, or positive. A total of 51 reviews were assessed, 17 of which were neutral and 34 positive. The methodological quality was low, with a median score of 23%. Nine of the 10 methodologically best reviews were positive. Other factors associated with a positive reviewers’ conclusion were review of spinal manipulation only, inclusion of a spinal manipulator in the review team, and a comprehensive literature search. The majority of the reviews concluded that spinal manipulation is an effective treatment for low back pain. Although, in particular, the reviews with a relatively high methodological quality had a positive conclusion, strong conclusions were precluded by the overall low quality of the reviews. More empirical research on the review methods applied to other therapies in other professional fields is needed to further explore our findings about the factors related to a positive reviewers’ conclusion

The effect of beta-carotene on the regression and progression of cervical dysplasia: A clinical experiment

In order to gain insight into the causality of the relation between β-carotene and cancer, we performed a randomized placebo-controlled trial in which the effect of β-carotene on the regression and progression rates of cervical dysplasia were examined. The experimental group (n = 137) received a supplemental dose of 10 mg of β-carotene daily for 3 months. The control group (n = 141) received placebo capsules. As the outcome parameter, two definitions of regression and progression were used, which were based on the degree of dysplasia before and after the medication period. The number of patients who showed progression was too small to allow conclusions. No effect of β-carotene on the regression percentages was observed: OR = 0.68 (95% CI: 0.28-1.60) using the broad definition; and OR = 1.22 (95% CI: 0.43-3.41) with the strict definition. A secondary analysis, in which the effect of the total intake of β-carotene (diet + medication) on the regression percentages of cervical dysplasia was studied, did not show a positive effect either. The paper discusses to what extent issues in the study design may have masked a potential effect and how our results affect the evidence for a causal relation between β-carotene and cancer