Inserm UMR1246 SPHERE

Universities of Nantes and Tours


SPHERE is a multidisciplinary unit that seeks to develop and validate methods that can be used in clinical or epidemiological studies.

The philosophy that drives the SPHERE unit is that the patient must be considered as a whole, i.e. taking into account his/her environment, and integrating his/her perceptions, experience, and wishes.

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4 axes of research

Axis 1

Cluster Randomized Trials and Complex Interventions

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Axis 2

Definition, selection, validation, and assessment of outcomes

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Axis 3

Methods for the measurement and interpretation of Self-Reported Outcomes

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Axis 4

Prediction and Causality

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PhD Training "Design, Analysis and Reporting of Cluster Randomised Trials"


The Digital Public Health Graduate Program is proposing the PhD training "Design, Analysis and Reporting of Cluster Randomised Trials" (CLUSTER) with professors Laurent Billot and Bruno Giraudeau (Université de Tours).

Lieu : Bordeaux

Impact of wagering inducements on the gambling behaviors of online gamblers: a longitudinal study based on gambling tracking data

Author(s) of the publication: Marianne Balem, Bastien Perrot, Jean-Benoit Hardouin, Elsa Thiabaud, Anaïs Saillard, Marie Grall-Bronnec, Gaëlle Challet-Bouju

Aims. To estimate whether the use of wagering inducements has a significant impact on the gambling behaviors of online gamblers and describe this temporal relation under naturalistic conditions. Design. This longitudinal observational study is part of the second stage of the Screening for Excessive Gambling Behaviors on the Internet (EDEIN) research program. Setting. Gambling tracking data from the French national online gambling authority (poker, horse race betting and sports betting) and from the French national lottery operator (lotteries and scratch games). Participants. A total of 9306 gamblers who played poker, horse race or sports betting and 5682 gamblers who played lotteries and scratch games completed an online survey. The gender ratio was largely male (around 90% for poker, horse race betting and sports betting and 65% for lotteries). Median age ranged from 35 (sports betting) to 53 (horse race betting and lotteries). Measurements. The survey used the Problem Gambling Severity Index (PGSI) to determine the status of the gamblers (at-risk or not). Gambling tracking data included weekly gambling intensity (wagers, deposits), gambling frequency (number of gambling days), proxies of at-risk gambling behaviors (chasing and breadth of involvement), and use of wagering inducements. Findings Use of wagering inducements was associated with an increase of gambling intensity (β between -0.06 [-0.08;-0.05] and 0.57 [0.54;0.60]), gambling frequency (β between 0.12 [0.10;0.18] and 0.29 [0.28;0.31]), and at-risk gambling behaviors (odds ratio between 1.32 [1.16;1.50] and 4.82 [4.61;5.05]) at the same week of their use. This effect was stronger for at-risk gambling behaviors and at-risk gamblers. Conclusions. Wagering inducements may represent a risk factor for developing or exacerbating gambling problems.

gambling tracking data, online gambling

Association of intracluster correlation measures with outcome prevalence for binary outcomes in cluster randomised trials

Author(s) of the publication: Mbekwe Yepnang, A. M., Caille, A., Eldridge, S. M., & Giraudeau, B

In cluster randomised trials, a measure of intracluster correlation such as the intraclass correlation coefficient (ICC) should be reported for each primary outcome. Providing intracluster correlation estimates may help in calculating sample size of future cluster randomised trials and also in interpreting the results of the trial from which they are derived. For a binary outcome, the ICC is known to be associated with its prevalence, which raises at least two issues. First, it questions the use of ICC estimates obtained on a binary outcome in a trial for sample size calculations in a subsequent trial in which the same binary outcome is expected to have a different prevalence. Second, it challenges the interpretation of ICC estimates because they do not solely depend on clustering level. Other intracluster correlation measures proposed for clustered binary data settings include the variance partition coefficient, the median odds ratio and the tetrachoric correlation coefficient. Under certain assumptions, the theoretical maximum possible value for an ICC associated with a binary outcome can be derived, and we proposed the relative deviation of an ICC estimate to this maximum value as another measure of the intracluster correlation. We conducted a simulation study to explore the dependence of these intracluster correlation measures on outcome prevalence and found that all are associated with prevalence. Even if all depend on prevalence, the tetrachoric correlation coefficient computed with Kirk’s approach was less dependent on the outcome prevalence than the other measures when the intracluster correlation was about 0.05. We also observed that for lower values, such as 0.01, the analysis of variance estimator of the ICC is preferred.

Statistical Methods in Medical Research