The test-negative design: Opportunities, limitations and biases.

The purpose of this paper is to investigate how to interpret the outcome of a test-negative design study. We does so by systematically reviewing the properties of the design in relation to its potential applications. We first argue that the application of the design does not depend on certain assumptions (as is sometimes articulated in the literature), which may open new opportunities for using the design. Then, we relate a number of limitations of the design. The design cannot be used for studying the mortality effects of vaccines and is problematic for studies into the effect on hospitalization. The vaccine's effectiveness on the transmission of viruses is also potentially problematic, depending very much on the characteristics of the tests. The implication of our findings is that the test-negative designs can, at best, be seen as an indication of effectiveness in highly idealized situations that are often far away from reality.

The Impact of a Group-Based Multidisciplinary Rehabilitation Program on the Quality of Life in Patients With Fibromyalgia: Results From the QUALIFIBRO Study.

BACKGROUND AND OBJECTIVE: Patients with fibromyalgia (FM) have a substantially reduced health-related quality of life (HRQoL). Their management should preferably focus on multidisciplinary nonpharmacological interventions. However, the long-term impact of such multicomponent therapies is not fully established. Waiting lists for patients seeking medical treatment are long, making individual-based approaches often unfeasible. The aim of our pragmatic study was to evaluate long-term HRQoL benefits of a comprehensive 8-week group-based multidisciplinary rehabilitation program focusing on patients' coping ability and self-care. METHODS: A total of 94 patients with clinically confirmed FM agreed to participate in this study. Before entering the program based on group-based cognitive behavioral therapy and graded activity training, patients completed questionnaires to screen for comorbidities. Health-related quality of life was assessed at the start, at 8 weeks, 6 months, and 1 year using the 36-Item Short-Form Health Survey instrument. Changes in HRQoL scores were analyzed according to linear mixed regression modeling. RESULTS: Baseline findings confirmed the substantially low physical and mental HRQoL in FM patients as well as high levels of depression, anxiety, and burnout. Only 2 patients left the program prematurely; 89% participated in the 1-year assessment. By the end of the program, HRQoL was significantly improved in all domains. This effect was maintained at 6 months and 1 year for all subscales. Changes at 1 year were greater in younger patients and those with depressive feelings before the start of treatment. CONCLUSIONS: Our group-based program offered to FM patients proved successful with significant improvements in their HRQoL both in the short and long term.