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Different Study Designs (different + study_design)

Distribution by Scientific Domains

Medical Sciences	75%

Selected Abstracts

Stratified case sampling and the use of family controls

GENETIC EPIDEMIOLOGY, Issue 3 2001
Kimberly D. Siegmund
Abstract We compare the asymptotic relative efficiency (ARE) of different study designs for estimating gene and gene-environment interaction effects using matched case-control data. In the sampling schemes considered, cases are selected differentially based on their family history of disease. Controls are selected either from unrelated subjects or from among the case's unaffected siblings and cousins. Parameters are estimated using weighted conditional logistic regression, where the likelihood contributions for each subject are weighted by the fraction of cases sampled sharing the same family history. Results showed that compared to random sampling, over-sampling cases with a positive family history increased the efficiency for estimating the main effect of a gene for sib-control designs (103,254% ARE) and decreased efficiency for cousin-control and population-control designs (68,94% ARE and 67,84% ARE, respectively). Population controls and random sampling of cases were most efficient for a recessive gene or a dominant gene with an relative risk less than 9. For estimating gene-environment interactions, over-sampling positive-family-history cases again led to increased efficiency using sib controls (111,180% ARE) and decreased efficiency using population controls (68,87% ARE). Using case-cousin pairs, the results differed based on the genetic model and the size of the interaction effect; biased sampling was only slightly more efficient than random sampling for large interaction effects under a dominant gene model (relative risk ratio = 8, 106% ARE). Overall, the most efficient study design for studying gene-environment interaction was the case-sib-control design with over-sampling of positive-family-history-cases. Genet. Epidemiol. 20:316,327, 2001. © 2001 Wiley-Liss, Inc. [source]

Probiotics and gastrointestinal diseases

JOURNAL OF INTERNAL MEDICINE, Issue 1 2005
Å. SULLIVAN
Abstract. There is increasing evidence indicating health benefits by consumption of foods containing microorganisms, i.e. probiotics. A number of clinical trials have been performed to evaluate the effects in the prevention and treatment of gastrointestinal diseases caused by pathogenic microorganisms or by disturbances in the normal microflora. Gastrointestinal infections caused by Helicobacter pylori, traveller's diarrhoea, rotavirus diarrhoea, antibiotic-associated diarrhoea (AAD) and Clostridium difficile -induced diarrhoea are conditions that have been studied. There are also studies performed on the preventive effect of probiotics on radiation-induced diarrhoea and diarrhoea in tube-fed patients. Inflammatory bowel disease and irritable bowel syndrome, two idiopathic conditions where alterations in the normal microflora have been implicated as responsible for initiation, are two further areas where the use of probiotics has been regarded as promising. The results from clinical studies have not been conclusive in that the effects of probiotics have been strain-dependent and different study designs have been used. Treatment of acute diarrhoea in children and prevention of AAD are the two most justified areas for the application of probiotics. [source]

The Canalith Repositioning Procedure for Benign Positional Vertigo: A Meta-Analysis,

THE LARYNGOSCOPE, Issue 7 2004
Bradford Alan Woodworth MD
Abstract Objective: To review the effectiveness of the canalith repositioning procedure (CRP) in the treatment of benign paroxysmal positional vertigo (BPPV) with a critical review of the literature and meta-analysis. Study Design: Meta-analysis. Methods: Studies eligible for inclusion were randomized, controlled trials of the CRP performed on clearly defined cases of BPPV. A total of nine studies meeting inclusion criteria were identified by two independent literature searches of Medline. Treatment and control groups were compared for symptom resolution and elimination of a positive Dix-Hallpike test. Results: Patients treated with CRP were more likely to demonstrate symptom resolution (odds ratio [OR] 4.6; 95% confidence interval [CI] 2.8,7.6) and negative Dix-Hallpike (OR 5.2; 95% CI 3.0,8.8) at the time of first follow-up. The effect of CRP for symptom improvement was strongest within the first month after treatment (OR 4.1; 95% CI 3.1,5.2) with some decline thereafter (OR 2.8; 95% CI 1.7,3.9). Conversely, the ability of CRP to produce a negative Dix-Hallpike strengthened between the first month after treatment (OR 3.0; 95% CI 1.8,4.0) and later follow-up times (OR 5.0; 95% CI 3.9,6.1). Conclusions: The CRP is more effective than control in resolving vertigo and positive Dix-Hallpike associated with BPPV. This finding was consistent among a variety of studies using different study designs. Untreated patients may demonstrate symptom improvement with time; however, many will continue to have a positive Dix-Hallpike when examined. Resolution of vertigo in untreated patients is therefore most likely because of avoidance of provocative positions. [source]

Accuracy of a newly developed integrated system for dental implant planning

CLINICAL ORAL IMPLANTS RESEARCH, Issue 11 2009
Timo Dreiseidler
Abstract Objectives: To evaluate the accuracy of the first integrated system for cone-beam CT (CBCT) imaging, dental implant planning and surgical template-aided implant placement. Materials and methods: On the basis of CBCT scans, a total of 54 implant positions were planned for 10 partially edentulous anatomical patient-equivalent models. Surgical guides were ordered from the manufacturer (SICAT). Two different types of guidance were assessed: for assessment of the SICAT system inherent accuracy vendor's titanium sleeves of 2 mm internal diameter and 5 mm length were utilized for pilot drills. The guide sleeves of the NobelGuide system were implemented for fully guided surgery and implant insertion. Deviations perpendicular to the implant axes at the crestal and apical end, as well as the angle deviations between the virtual planning data and the surgical results, were measured utilizing a follow-up CBCT investigation and referential marker-based registration. Results: The SICAT system inherent mean deviation rates for the drilled pilot osteotomies were determined to be smaller than 500 ,m even at the apical end. Mean angle deviations of 1.18° were determined. Utilizing the NobelGuide sleeve-in-sleeve system for fully guided implant insertion in combination with the investigated template technology enabled to insert dental implants with the same accuracy. Crestal deviations, in general, were significantly lower than the apical deviations. Conclusion: Although hardly comparable due to different study designs and measurement strategies, the investigated SICAT system's inherent accuracy corresponds to the most favourable results for computer-aided surgery systems published so far. In combination with the NobelGuide surgical set for fully guided insertion, the same accuracy level could be maintained for implant positioning. [source]