Efficiency Issues among Statistical Methods for Demonstrating Efficacy of Caries Prevention

Assessing outcomes of large-scale public health interventions in the absence of baseline data using a mixture of Cox and binomial regressions

Background

Large-scale public health interventions with rapid scale-up are increasingly being implemented worldwide. Such implementation allows for a large target population to be reached in a short period of time. But when the time comes to investigate the effectiveness of these interventions, the rapid scale-up creates several methodological challenges, such as the lack of baseline data and the absence of control groups. One example of such an intervention is Avahan, the India HIV/AIDS initiative of the Bill & Melinda Gates Foundation. One question of interest is the effect of Avahan on condom use by female sex workers with their clients. By retrospectively reconstructing condom use and sex work history from survey data, it is possible to estimate how condom use rates evolve over time. However formal inference about how this rate changes at a given point in calendar time remains challenging.

Methods

We propose a new statistical procedure based on a mixture of binomial regression and Cox regression. We compare this new method to an existing approach based on generalized estimating equations through simulations and application to Indian data.

Results

Both methods are unbiased, but the proposed method is more powerful than the existing method, especially when initial condom use is high. When applied to the Indian data, the new method mostly agrees with the existing method, but seems to have corrected some implausible results of the latter in a few districts. We also show how the new method can be used to analyze the data of all districts combined.

Conclusions

The use of both methods can be recommended for exploratory data analysis. However for formal statistical inference, the new method has better power.

Statistical power of multilevel modelling in dental caries clinical trials: a simulation study

Outcome data from dental caries clinical trials have a naturally hierarchical structure, with surfaces clustered within teeth, clustered within individuals. Data are often aggregated into the DMF index for each individual, losing tooth- and surface-specific information. If these data are to be analysed by tooth or surface, allowing exploration of effects of interventions on different teeth and surfaces, appropriate methods must be used to adjust for the clustered nature of the data. Multilevel modelling allows analysis of clustered data using individual observations without aggregating data, and has been little used in the field of dental caries. A simulation study was conducted to investigate the performance of multilevel modelling methods and standard caries increment analysis. Data sets were simulated from a three-level binomial distribution based on analysis of a caries clinical trial in Scottish adolescents, with varying sample sizes, treatment effects and random tooth level effects based on trials reported in Cochrane reviews of topical fluoride, and analysed to compare the power of multilevel models and traditional analysis. 40,500 data sets were simulated. Analysis showed that estimated power for the traditional caries increment method was similar to that for multilevel modelling, with more variation in smaller data sets. Multilevel modelling may not allow significant reductions in the number of participants required in a caries clinical trial, compared to the use of traditional analyses, but investigators interested in exploring the effect of their intervention in more detail may wish to consider the application of multilevel modelling to their clinical trial data.

Influence of network topology on sound propagation in granular materials

Granular media, whose features range from the particle scale to the force-chain scale and the bulk scale, are usually modeled as either particulate or continuum materials. In contrast with each of these approaches, network representations are natural for the simultaneous examination of microscopic, mesoscopic, and macroscopic features. In this paper, we treat granular materials as spatially embedded networks in which the nodes (particles) are connected by weighted edges obtained from contact forces. We test a variety of network measures to determine their utility in helping to describe sound propagation in granular networks and find that network diagnostics can be used to probe particle-, curve-, domain-, and system-scale structures in granular media. In particular, diagnostics of mesoscale network structure are reproducible across experiments, are correlated with sound propagation in this medium, and can be used to identify potentially interesting size scales. We also demonstrate that the sensitivity of network diagnostics depends on the phase of sound propagation. In the injection phase, the signal propagates systemically, as indicated by correlations with the network diagnostic of global efficiency. In the scattering phase, however, the signal is better predicted by mesoscale community structure, suggesting that the acoustic signal scatters over local geographic neighborhoods. Collectively, our results demonstrate how the force network of a granular system is imprinted on transmitted waves.

A model for the analysis of caries occurrence in primary molar tooth surfaces

Recently methods of caries quantification in the primary dentition have moved away from summary 'whole mouth' measures at the individual level to methods based on generalised linear modelling (GLM) approaches or survival analysis approaches. However, GLM approaches based on logistic transformation fail to take into account the time-dependent process of tooth/surface survival to caries. There may also be practical difficulties associated with casting parametric survival-based approaches in a complex multilevel hierarchy and the selection of an optimal survival distribution, while non-parametric survival methods are not generally suitable for the assessment of supplementary information recorded on study participants. In the current investigation, a hybrid semi-parametric approach comprising elements of survival-based and GLM methodologies suitable for modelling of caries occurrence within fixed time periods is assessed, using an illustrative multilevel data set of caries occurrence in primary molars from a cohort study, with clustering of data assumed to occur at surface and tooth levels. Inferences of parameter significance were found to be consistent with previous parametric survival-based analyses of the same data set, with gender, socio-economic status, fluoridation status, tooth location, surface type and fluoridation status-surface type interaction significantly associated with caries occurrence. The appropriateness of the hierarchical structure facilitated by the hybrid approach was also confirmed. Hence the hybrid approach is proposed as a more appropriate alternative to primary caries modelling than non-parametric survival methods or other GLM-based models, and as a practical alternative to more rigorous survival-based methods unlikely to be fully accessible to most researchers.

Oral health-related quality of life in Czech population

OBJECTIVE

The purpose of this study was to assess the oral health-related quality of life in Czech population.

METHODS

Data were collected from 1,380 subjects aged 30 to 69 years attending the Department of Dentistry, Medical Faculty of Charles University in Hradec Králové or attending three private dental practitioners collaborating on the study. Oral health-related quality of life was measured with the Oral Health Impact Profile (OHIP-14) questionnaire that was translated to Czech. The OHIP-14 scores were assessed in relation to chosen clinical and sociodemographic characteristics and oral health behaviour. Statistical analyses included descriptive analyses, the Mann-Whitney test, the Kolmogorov-Smirnov test and the Kruskal-Wallis test using the NCSS 2007 program. The chi2 test of independence in contingency tables or Fisher's exact test was used for qualitative data.

RESULTS

Internal reliability for the 14 items overall was very high (Cronbach's ac = 0.924). The two most frequently scored items using the answer other than "never" during the last year were "painful aching" (62% of subjects) and "uncomfortable to eat" (44.4%), representing subdomain physical pain. The domain of social disability was reported least frequently. The OHIP-14 was significantly associated with dental status, dental behaviour, income and age.

CONCLUSIONS

The findings of this study do suggest that the culturally adapted OHIP-14 version may be a good research instrument to be considered for use in measuring the impact of oral problems on the quality of life in Czech population.

Incidência de cárie dentária em adolescentes em município do Nordeste brasileiro, 2006

O presente estudo teve como objetivo analisar a incidência da cárie dentária em adolescentes associada à condição sócio-econômica, acesso a serviços e autopercepção. É um estudo longitudinal por meio de levantamento epidemiológico de cárie e questionário estruturado com amostra composta por 688 adolescentes residentes no Município de Sobral, Ceará, Brasil. A incidência aumentou progressivamente com a idade, passando de 1,60 nos adolescentes com 12 anos até 2,28 para os com 15 anos, registrando-se uma incidência média de 1,86 dentes cariados por adolescente. Entre as variáveis estudadas, dor de dente nos últimos seis meses [RR = 1,46 (1,22-1,76)], merenda escolar [RR = 1,45 (1,21-1,74)], freqüência de consulta ao dentista [RR = 1,48 (1,33-1,79)] e acesso à unidade de saúde [RR = 1,21 (1,01-1,45)], ajustadas por morbidade referida apresentaram relação com a alta incidência de cárie. É fundamental que gestores e profissionais de saúde formulem políticas públicas que não se restrinjam a aspectos como atendimento clínico e prevenção de doenças, estimulando a população na luta pela conquista por melhores condições de vida, viabilizando eqüidade no acesso aos serviços e desenvolvendo uma gestão coletiva das ações de saúde.

Comparison of the effectiveness of fissure sealants in Finland, Sweden, and Greece

OBJECTIVE

To evaluate the effectiveness of sealant treatment in preventing dental restorations due to caries in a practice-based research network in Finland, Sweden, and Greece.

MATERIAL AND METHODS

Times of tooth emergence, sealing treatment, and dental caries were compiled from the dental charts of 4735 subjects born in 1970-72 in Finland and in 1980-82 in Finland, Sweden, and Greece. Survival time between tooth emergence and placement of first restoration was measured and estimated using survival analysis methodology.

RESULTS

At the end of follow-up (7-10+ years), 30-40% of sealed molars and 60-80% of non-sealed molars were restored. Early sealant placement compared to late sealing did not result in significantly higher survival of 1st molars. The strategy of sealing the 1st molars only in high caries risk subjects was as effective as sealing all the molars and premolars routinely without caries risk determination.

CONCLUSIONS

The sealing of all molar fissures proved to be no more effective than sealing risk fissures of subjects. Early sealing did not result in any better outcome than late sealing. The effectiveness of sealant treatment in preventing dental restorations is dependent on the caries risk of individuals and caries prevalence of the country.

Chlorhexidine and Preservation of Sound Tooth Structure in Older Adults

The Trial to Enhance Elderly Teeth Health (TEETH) was designed to test the impact of regular rinsing with a 0.12% chlorhexidine (CHX) solution on tooth loss, and the causes of tooth loss (caries, periodontal disease and trauma) were also investigated. This paper reports on the effectiveness of a 0.12% CHX solution for controlling caries using a tooth surface (coronal and root) survival analysis. A total of 1,101 low income elders in Seattle (United States) and Vancouver (Canada), aged 60-75 years, were recruited for a double-blind clinical trial and assigned to either a CHX (n = 550) or a placebo (n = 551) mouth rinse. Subjects alternated between daily rinsing for 1 month, followed by weekly rinsing for 5 months. All sound coronal and root surfaces at baseline were followed annually for up to 5 years. At each follow-up examination, those tooth surfaces with caries, restored, or extracted were scored as 'carious'. The hazard ratio associated with CHX for a sound surface to become filled, decayed, or extracted was 0.87 for coronal surfaces (95% confidence interval: 0.71-1.14, p = 0.20) and 0.91 for root surfaces (95% confidence interval: 0.73-1.14, p = 0.41). These findings suggest that regular rinsing with CHX does not have a substantial effect on the preservation of sound tooth structure in older adults.

The classic caries clinical trial: constraints and opportunities

The history of clinical trials would include events in 1747 on board the Salisbury, a British Navy vessel at sea with 12 seamen critically ill with scurvy. Involving these 12 sailors in a study, an officer on board by the name of Lind evaluated six potential treatments for scurvy, and rapidly reached the conclusion that daily consumption of citrus fruits returned the men fit for duty in approximately six days (Bull, 1959). The concept of experimental randomization was first developed by Sir R.A. Fisher (1925, 1926), and the method was introduced to medical research via a study of tuberculosis treatment by Amberson and co-workers (1931), who randomized 24 TB patients into two groups, one to receive the experimental therapy, the other serving as the control. Amberson et al. also incorporated the concept of blinding into their study. Sir Austin Bradford Hill codified and built on the principles of scientific experimentation developed by Fisher, and introduced the use of random numbers in the allocation of patients in the British Medical Research Council (1948) study of the effect of streptomycin in the treatment of tuberculosis (Daniels and Hill, 1952; Hill, 1952). The first applications of clinical trial methodology for testing interventions on dental, oral, and maxillofacial diseases and conditions are more difficult to determine. For dental caries prevention, however, Chilton and Fertig (1958) and Slack and Martin (1964) were certainly among the early caries clinical trial pioneers. As clinical trials have come into the mainstream of clinical research in medicine and dentistry, a great deal of developmental work has focused on their methodological enhancement. The most successful of these efforts have come from fruitful, ongoing collaborations among clinician investigators, biostatisticians, data management specialists, biomedical ethicists, and others with an academic interest in clinical trial design and utilization. During the past 25 years, the emergence of systematic reviews and the evidence-based medicine (EBM) movement have also contributed significantly to the increasing reliance on randomized clinical trial outcomes for the advancement of better clinical practice (Richards et al., 1997; Straus and Sackett, 1998; www.cochrane.org/cochrane/ccbroch.htm#BDL, 2002).