Power and Sample Size in Multilevel Linear Models

2005 ◽  
Author(s):  
Tom A. B. Snijders
Keyword(s):  
Sample Size ◽  
Linear Models ◽  
Multilevel Linear Models

scholarly journals Clinical Factors Influencing the Efficacy of Systemic Moxifloxacin in the Therapy of Patients With Generalized Aggressive Periodontitis: A Multilevel Analysis From a Clinical Trial

2015 ◽  
Vol 8 (3) ◽  
pp. 80 ◽  
Author(s):  
Carlos M. Ardila ◽  
Isabel C. Guzmán
Keyword(s):  
Clinical Trial ◽  
Multilevel Analysis ◽  
Linear Models ◽  
Clinical Results ◽  
Aggressive Periodontitis ◽  
Continuous Variables ◽  
Clinical Factors ◽  
Probing Depth ◽  
Clinical Benefits ◽  
Multilevel Linear Models

<p><strong>BACKGROUND:</strong> It has been reported that clinical results of mechanical periodontal treatment could differ between subjects and among different sites of the tooth in the patient. The objective of this multilevel analysis is to investigate clinical factors at subject and sites of the tooth that influence variations in clinical attachment (CAL) increase and probing depth (PD) diminution of adjunctive moxifloxacin (MOX) at six months post-treatment in generalized aggressive periodontitis.</p> <p><strong>METHODS:</strong> This clinical trial included 40 patients randomly distributed to two therapy protocols: scaling and root planing alone or combined with MOX. Multilevel linear models for continuous variables were formulated to evaluate the clinical impact of the hierarchical configuration of periodontal data.</p> <p><strong>RESULTS:</strong> Six months following therapy, the divergences between both protocols were statistically significant in PD diminution and CAL increase, favouring the MOX therapy (p&lt;0.001). Besides, the multilevel analysis revealed that adjunctive MOX at the subject level, non-molar and the interaction non-molar x MOX at the tooth level, interproximal sites and the interaction interproximal sites x MOX at the site level, were statistically significant factors in determining CAL increase and PD diminution.</p> <p><strong>CONCLUSIONS:</strong> The main cause of variability in CAL gain and PD reduction following adjunctive MOX was attributable to the tooth level. Adjunctive MOX and their interactions with non-molar and interproximal sites showed higher clinical benefits at the tooth and site levels which could be essential for PD reduction and CAL gain in generalized aggressive periodontitis subjects.</p>

scholarly journals On the variance parameter estimator in general linear models

Metrika ◽  
2019 ◽  
Vol 83 (2) ◽  
pp. 243-254
Author(s):  
Mathias Lindholm ◽  
Felix Wahl
Keyword(s):  
Sample Size ◽  
Linear Models ◽  
General Linear ◽  
Finite Sample ◽  
Parameter Estimator ◽  
General Linear Models ◽  
Vector Autoregressive ◽  
Finite Sample Size ◽  
Error Terms ◽  
Variance Parameter

Abstract In the present note we consider general linear models where the covariates may be both random and non-random, and where the only restrictions on the error terms are that they are independent and have finite fourth moments. For this class of models we analyse the variance parameter estimator. In particular we obtain finite sample size bounds for the variance of the variance parameter estimator which are independent of covariate information regardless of whether the covariates are random or not. For the case with random covariates this immediately yields bounds on the unconditional variance of the variance estimator—a situation which in general is analytically intractable. The situation with random covariates is illustrated in an example where a certain vector autoregressive model which appears naturally within the area of insurance mathematics is analysed. Further, the obtained bounds are sharp in the sense that both the lower and upper bound will converge to the same asymptotic limit when scaled with the sample size. By using the derived bounds it is simple to show convergence in mean square of the variance parameter estimator for both random and non-random covariates. Moreover, the derivation of the bounds for the above general linear model is based on a lemma which applies in greater generality. This is illustrated by applying the used techniques to a class of mixed effects models.

scholarly journals Association between environmental stimulation and apathy in nursing home residents with dementia

2019 ◽  
Vol 31 (08) ◽  
pp. 1109-1120 ◽  
Author(s):  
Ying-Ling Jao ◽  
Wen Liu ◽  
Kristine Williams ◽  
Habib Chaudhury ◽  
Jyotsana Parajuli
Keyword(s):  
Nursing Home ◽  
Linear Models ◽  
Rating Scale ◽  
Nursing Home Residents ◽  
Repeated Measure ◽  
Future Research ◽  
Video Observations ◽  
Environmental Stimulation ◽  
Multilevel Linear Models ◽  
Environmental Feedback

ABSTRACTObjectives:Prior research and theories established the link between care environments and apathy. Yet, empirical evidence on how environmental stimulation impacts apathy is lacking. This study examined the association between environmental stimulation and apathy in nursing home residents with dementia.Design:This repeated-measure study analyzed 104 video observations of staff caregiver–resident interactions.Setting:12 nursing homes.Participants:63 unique staff caregiver–resident dyads that involved 42 caregivers and 44 residents with moderate to severe dementia.Measurements:Second-by-second behavioral coding using Noldus Observer software was conducted to assess apathy and environmental stimulation, using the Person-Environment Apathy Rating scale. The environment subscale includes six items: stimulation clarity, stimulation strength, stimulation specificity, interaction involvement, physical accessibility, and environmental feedback. The apathy subscale includes six items: facial expression, eye contact, physical engagement, purposeful activity, verbal tone, and verbal expression. Multilevel linear models were used for analysis.Results:Results showed that apathy was not associated with the overall quality of environmental stimulation but was significantly associated with stimulation specificity (coefficient = −2.23,p= 0.049). However, the association was not significant after controlling for resident characteristics (p= 0.082). In addition, higher levels of environmental feedback were associated with lower apathy levels (coefficient = −2.14,p= 0.001). The association remained significant after controlling for resident characteristics (coefficient = −1.65,p= 0.014).Conclusion:Findings reveal that when environmental stimulation is individually tailored and prompts engagement, residents are less apathetic. This study highlights the effect of environmental stimulation on apathy. Future research should explore interventions that modify environmental stimulation to reduce apathy and improve dementia care.

Quality of Split-Mouth Trials in Dentistry: 1998, 2008, and 2018

2020 ◽  
Vol 99 (13) ◽  
pp. 1453-1460
Author(s):  
D. Qin ◽  
F. Hua ◽  
H. He ◽  
S. Liang ◽  
H. Worthington ◽  
...  
Keyword(s):  
Sample Size ◽  
Methodological Quality ◽  
Linear Models ◽  
Sample Size Calculation ◽  
Reporting Quality ◽  
Treatment Groups ◽  
Item Checklist ◽  
The Mean ◽  
Over Time

The objectives of this study were to assess the reporting quality and methodological quality of split-mouth trials (SMTs) published during the past 2 decades and to determine whether there has been an improvement in their quality over time. We searched the MEDLINE database via PubMed to identify SMTs published in 1998, 2008, and 2018. For each included SMT, we used the CONsolidated Standards Of Reporting Trials (CONSORT) 2010 guideline, CONSORT for within-person trial (WPT) extension, and a new 3-item checklist to assess its trial reporting quality (TRQ), WPT-specific reporting quality (WRQ), and SMT-specific methodological quality (SMQ), respectively. Multivariable generalized linear models were performed to analyze the quality of SMTs over time, adjusting for potential confounding factors. A total of 119 SMTs were included. The mean overall score for the TRQ (score range, 0 to 32), WRQ (0 to 15), and SMQ (0 to 3) was 15.77 (SD 4.51), 6.06 (2.06), and 1.12 (0.70), respectively. The primary outcome was clearly defined in only 28 SMTs (23.5%), and only 27 (22.7%) presented a replicable sample size calculation. Only 45 SMTs (37.8%) provided the rationale for using a split-mouth design. The correlation between body sites was reported in only 5 studies (4.2%) for sample size calculation and 4 studies (3.4%) for statistical results. Only 2 studies (1.7%) performed an appropriate sample size calculation, and 46 (38.7%) chose appropriate statistical methods, both accounting for the correlation among treatment groups and the clustering/multiplicity of measurements within an individual. Results of regression analyses suggested that the TRQ of SMTs improved significantly with time ( P < 0.001), while there was no evidence of improvement in WRQ or SMQ. Both the reporting quality and methodological quality of SMTs still have much room for improvement. Concerted efforts are needed to improve the execution and reporting of SMTs.

Sample Size Choice: Charts for Experiments With Linear Models

Technometrics ◽  
1993 ◽  
Vol 35 (2) ◽  
pp. 234-235
Author(s):  
Michael R. Emptage
Keyword(s):  
Sample Size ◽  
Linear Models

scholarly journals Knowledge of Dental Academics about the COVID-19 Pandemic: A Multi-Country Online Survey

2020 ◽  
Author(s):  
Nour Ammar ◽  
Nourhan M. Aly ◽  
Morenike O. Folayan ◽  
Simin Z. Mohebbi ◽  
Sameh Attia ◽  
...  
Keyword(s):  
Living Arrangements ◽  
Online Survey ◽  
Linear Models ◽  
Dental Treatment ◽  
Diagnostic Methods ◽  
Cross Sectional ◽  
Country Level ◽  
Global Pandemic ◽  
The Mean ◽  
Multilevel Linear Models

Abstract Background: COVID-19 is a global pandemic affecting all aspects of life in all countries. We assessed COVID-19 knowledge and associated factors among dental academics in various countries. Method: We invited dental academics to participate in a cross-sectional, multi-country, online survey from March to April 2020. The survey assessed knowledge of COVID-19 regarding the mode of transmission, symptoms, diagnosis, treatment, protection, and dental treatment precautions as well as participants’ background variables. The analysis was based on multilevel linear models to assess the association between knowledge and factors at individual levels (personal and professional) and country-level (number of COVID-19 cases/ million population), accounting for random variation among countries. Results: Two thousand forty-five academics from 26 countries participated in the survey (response rate= 14.3%, with 54.7% female and 67% younger than 46 years of age). The mean (SD) knowledge percent score was 73.2% (11.2), and the knowledge of symptoms score was significantly lower than the diagnostic methods score (53.1% and 85.4%). Knowledge was significantly higher among those living with partner/spouse than those living alone (regression coefficient (B)= 0.48); those with PhD than those with BDS (B= 0.48), those seeing 21 to 30 patients daily than those seeing no patients (B= 0.65) and those from countries with a higher number of COVID-19 cases/million population (B= 0.0007). Conclusions: Dental academics had poorer knowledge of COVID-19 symptoms than diagnostic methods. Living arrangements, academic degrees, patient load, and magnitude of epidemic in the country were associated with COVD-19 knowledge among dental academics. COVID-19 training can be designed using these factors to target academics with the greatest need.

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