A simulation study of sample size for multilevel logistic regression models

<p>Abstract</p> <p>Background</p> <p>Many studies conducted in health and social sciences collect individual level data as outcome measures. Usually, such data have a hierarchical structure, with patients clustered within physicians, and physicians clustered within practices. Large survey data, including national surveys, have a hierarchical or clustered structure; respondents are naturally clustered in geographical units (e.g., health regions) and may be grouped into smaller units. Outcomes of interest in many fields not only reflect continuous measures, but also binary outcomes such as depression, presence or absence of a disease, and self-reported general health. In the framework of multilevel studies an important problem is calculating an adequate sample size that generates unbiased and accurate estimates.</p> <p>Methods</p> <p>In this paper simulation studies are used to assess the effect of varying sample size at both the individual and group level on the accuracy of the estimates of the parameters and variance components of multilevel logistic regression models. In addition, the influence of prevalence of the outcome and the intra-class correlation coefficient (ICC) is examined.</p> <p>Results</p> <p>The results show that the estimates of the fixed effect parameters are unbiased for 100 groups with group size of 50 or higher. The estimates of the variance covariance components are slightly biased even with 100 groups and group size of 50. The biases for both fixed and random effects are severe for group size of 5. The standard errors for fixed effect parameters are unbiased while for variance covariance components are underestimated. Results suggest that low prevalent events require larger sample sizes with at least a minimum of 100 groups and 50 individuals per group.</p> <p>Conclusion</p> <p>We recommend using a minimum group size of 50 with at least 50 groups to produce valid estimates for multi-level logistic regression models. Group size should be adjusted under conditions where the prevalence of events is low such that the expected number of events in each group should be greater than one.</p

Improving preventive service delivery at adult complete health check-ups: the Preventive health Evidence-based Recommendation Form (PERFORM) cluster randomized controlled trial

BACKGROUND: To determine the effectiveness of a single checklist reminder form to improve the delivery of preventive health services at adult health check-ups in a family practice setting. METHODS: A prospective cluster randomized controlled trial was conducted at four urban family practice clinics among 38 primary care physicians affiliated with the University of Toronto. Preventive Care Checklist Forms(© )were created to be used by family physicians at adult health check-ups over a five-month period. The sex-specific forms incorporate evidence-based recommendations on preventive health services and documentation space for routine procedures such as physical examination. The forms were used in two intervention clinics and two control clinics. Rates and relative risks (RR) of the performance of 13 preventive health maneuvers at baseline and post-intervention and the percentage of up-to-date preventive health services delivered per patient were compared between the two groups. RESULTS: Randomly-selected charts were reviewed at baseline (n = 509) and post-intervention (n = 608). Baseline rates for provision of preventive health services ranged from 3% (fecal occult blood testing) to 93% (blood pressure measurement), similar to other settings. The percentage of up-to-date preventive health services delivered per patient at the end of the intervention was 48.9% in the control group and 71.7% in the intervention group. This is an overall 22.8% absolute increase (p = 0.0001), and 46.6% relative increase in the delivery of preventive health services per patient in the intervention group compared to controls. Eight of thirteen preventive health services showed a statistically significant change (p < 0.05) in favor of the intervention (adjusted RR (95% C.I.)): counseling on brushing/flossing teeth (9.2 (4.3–19.6)), folic acid counseling (7.5 (2.7–20.8)), fecal occult blood testing (6.7 (1.9–24.1)), smoking cessation counseling (3.9 (2.2–7.2)), tetanus immunization (3.0 (1.7–5.2)), history of alcohol intake (1.33 (1.2–1.5)), history of smoking habits (1.28 (1.2–1.4)) and blood pressure measurement (1.05 (1.00–1.10)). CONCLUSION: This simple, low cost, clinically relevant intervention improves the delivery of preventive health services by prompting physicians of evidence-based recommendations in a checklist format that incorporates existing practice patterns. Periodic updates of the Preventive Care Checklist Forms(© )will allow a feasible and easy-to-use tool for primary care physicians to provide evidence-based preventive health services to adults at routine health check-ups. The forms can also be incorporated into an electronic health record. The Preventive Care Checklist Forms(© )are accessible in English and French at the College of Family Physicians of Canada web site

Measuring change in health status of older adults at the population level: The transition probability model

BACKGROUND: The current demographic transition will lead to increasing demands on health services. However, debate exists as to the role age plays relative to co-morbidity in terms of health services utilization. While age has been identified as a critical factor in health services utilization, health services utilization is not simply an outcome of ill health, nor is it an inevitable outcome of aging. Most data on health service utilization studies assess utilization at one point in time, and does not examine transitions in health service utilization. We sought to measure health services utilization and to investigate patterns in the transition of levels of utilization and outcomes associated with different levels of utilization. METHODS: We conducted a population-based retrospective cohort study of all Ontario residents aged 65+ eligible for public healthcare coverage from January 1998-December 2006. The main outcome measure was total number of utilization events. The total is computed by summing, on a per annum basis, the number of family physician visits, specialist visits, Emergency Department visits, drug claims, lab claims, X-rays, CT scans, MRI scans, and inpatient admissions. Three categories of utilization were created: low, moderate, and high. RESULTS: There is heterogeneity in health services utilization across the late lifespan. Utilization increased consistently in the 9-year study period. The probability of remaining at the high utilization category when the person was in the high category the previous year was more than 0.70 for both males and females and for all age groups. Overall healthcare utilization increases more rapidly among the high users compared to the low users. There was negligible probability for moving from high to low utilization category. Probability of death increased exponentially as age increased. Older adults in the low utilization category had the lowest probability of death. The number of male nonagenarians increased more rapidly than female nonagenarians. CONCLUSION: There are measurable and identifiable differences in the patterns of health services utilization among older adults. This data will permit clinicians and policy makers to tailor interventions appropriate to the risk class of patients

Accuracy of magnetic resonance imaging for measuring maturing cartilage: A phantom study

OBJECTIVES: To evaluate the accuracy of magnetic resonance imaging measurements of cartilage tissue-mimicking phantoms and to determine a combination of magnetic resonance imaging parameters to optimize accuracy while minimizing scan time. METHOD: Edge dimensions from 4 rectangular agar phantoms ranging from 10.5 to 14.5 mm in length and 1.25 to 5.5 mm in width were independently measured by two readers using a steel ruler. Coronal T1 spin echo (T1 SE), fast spoiled gradient-recalled echo (FSPGR) and multiplanar gradient-recalled echo (GRE MPGR) sequences were used to obtain phantom images on a 1.5-T scanner. RESULTS: Inter- and intra-reader reliability were high for both direct measurements and for magnetic resonance imaging measurements of phantoms. Statistically significant differences were noted between the mean direct measurements and the mean magnetic resonance imaging measurements for phantom 1 when using a GRE MPGR sequence (512x512 pixels, 1.5-mm slice thickness, 5:49 min scan time), while borderline differences were noted for T1 SE sequences with the following parameters: 320x320 pixels, 1.5-mm slice thickness, 6:11 min scan time; 320x320 pixels, 4-mm slice thickness, 6:11 min scan time; and 512x512 pixels, 1.5-mm slice thickness, 9:48 min scan time. Borderline differences were also noted when using a FSPGR sequence with 512x512 pixels, a 1.5-mm slice thickness and a 3:36 min scan time. CONCLUSIONS: FSPGR sequences, regardless of the magnetic resonance imaging parameter combination used, provided accurate measurements. The GRE MPGR sequence using 512x512 pixels, a 1.5-mm slice thickness and a 5:49 min scan time and, to a lesser degree, all tested T1 SE sequences produced suboptimal accuracy when measuring the widest phantom

Would you like to add a weight after this blood pressure, doctor? Discovery of potentially actionable associations between the provision of multiple screens in primary care

The CPCSSN was funded through a contribution agreement with the Public Health Agency of Canada.Rationale, aims, and objective:  Guidelines recommend screening for risk factors associated with chronic diseases but current electronic prompts have limited effects. Our objective was to discover and rank associations between the presence of screens to plan more efficient prompts in primary care. Methods:  Risk factors with the greatest impact on chronic diseases are associated with blood pressure, body mass index, waist circumference, glycaemic and lipid levels, smoking, alcohol use, diet, and exercise. We looked for associations between the presence of screens for these in electronic medical records. We used association rule mining to describe relationships among items, factor analysis to find latent categories, and Cronbach α to quantify consistency within latent categories. Results:  Data from 92 140 patients in or around Toronto, Ontario, were included. We found positive correlations (lift >1) between the presence of all screens. The presence of any screen was associated with confidence greater than 80% that other data on items with high prevalence (blood pressure, glycaemic and lipid levels, or smoking) would also be present. A cluster of rules predicting the presence of blood pressure were ranked highest using measures of interestingness such as standardized lift. We found 3 latent categories using factor analysis; these were laboratory tests, vital signs, and lifestyle factors; Cronbach α ranged between .58 for lifestyle factors and .88 for laboratory tests. Conclusions:  Associations between the provision of important screens can be discovered and ranked. Rules with promising combinations of associated screens could be used to implement data driven alerts.Publisher PDFPeer reviewe

Sonographic Assessment of Renal Growth in Patients with Beckwith-Wiedemann Syndrome: The Beckwith-Wiedemann Syndrome Renal Nomogram

BACKGROUND: Beckwith-Wiedemann syndrome is a disorder of somatic overgrowth. Evidence of kidney overgrowth is a diagnostic criterion that may be used to help identify those patients who are at the greatest risk of developing Wilms tumors. In such subjects, kidney size is typically larger than that of age-matched normal controls. OBJECTIVE: The purpose of our study was to generate a nomogram that could be used to measure renal dimensions in children with Beckwith-Wiedemann syndrome in a clinical setting. MATERIALS & METHODS: All of the Beckwith-Wiedemann syndrome patients followed at our institution from 1996 to 2004 were eligible for inclusion in our study. Renal length was measured with a curvilinear transducer and with the patient supine. Renal lengths were measured for both kidneys using real-time ultrasound for all patients. Their data were compared with those of age-matched controls reported in the 1984 study by Rosenbaum et al. RESULTS: Ninety-six children with Beckwith-Wiedemann syndrome were followed from 1996 to 2004. Forty-three of these patients met our criteria for inclusion in the study: 28 girls (65%) and 15 boys (35%). We identified a linear relationship between kidney length and patient age. No statistically significant differences in renal length were found between boys and girls (p=0.2153) or between the kidneys on either side of the body (p=0.9613). CONCLUSION: Our study provides a practical, simple renal growth chart that offers a reasonable, sensitive method for evaluating kidney size in children with Beckwith-Wiedemann syndrome

Improving chronic disease prevention and screening in primary care: results of the BETTER pragmatic cluster randomized controlled trial.

BackgroundPrimary care provides most of the evidence-based chronic disease prevention and screening services offered by the healthcare system. However, there remains a gap between recommended preventive services and actual practice. This trial (the BETTER Trial) aimed to improve preventive care of heart disease, diabetes, colorectal, breast and cervical cancers, and relevant lifestyle factors through a practice facilitation intervention set in primary care.MethodsPragmatic two-way factorial cluster RCT with Primary Care Physicians' practices as the unit of allocation and individual patients as the unit of analysis. The setting was urban Primary Care Team practices in two Canadian provinces. Eight Primary Care Team practices were randomly assigned to receive the practice-level intervention or wait-list control; 4 physicians in each team (32 physicians) were randomly assigned to receive the patient-level intervention or wait-list control. Patients randomly selected from physicians' rosters were stratified into two groups: 1) general and 2) moderate mental illness. The interventions involved a multifaceted, evidence-based, tailored practice-level intervention with a Practice Facilitator, and a patient-level intervention involving a one-hour visit with a Prevention Practitioner where patients received a tailored 'prevention prescription'. The primary outcome was a composite Summary Quality Index of 28 evidence-based chronic disease prevention and screening actions with pre-defined targets, expressed as the ratio of eligible actions at baseline that were met at follow-up. A cost-effectiveness analysis was conducted.Results789 of 1,260 (63%) eligible patients participated. On average, patients were eligible for 8.96 (SD 3.2) actions at baseline. In the adjusted analysis, control patients met 23.1% (95% CI: 19.2% to 27.1%) of target actions, compared to 28.5% (95% CI: 20.9% to 36.0%) receiving the practice-level intervention, 55.6% (95% CI: 49.0% to 62.1%) receiving the patient-level intervention, and 58.9% (95% CI: 54.7% to 63.1%) receiving both practice- and patient-level interventions (patient-level intervention versus control, P &lt; 0.001). The benefit of the patient-level intervention was seen in both strata. The extra cost of the intervention was $26.43CAN (95$16 to $44) per additional action met.ConclusionsA Prevention Practitioner can improve the implementation of clinically important prevention and screening for chronic diseases in a cost-effective manner

Geospatial inequalities and determinants of nutritional status among women and children in Afghanistan: An observational study

Background: Undernutrition is a pervasive condition in Afghanistan, and prevalence is among the highest in the world. We aimed to comprehensively assess district-level geographical disparities and determinants of nutritional status (stunting, wasting, or underweight) among women and children in Afghanistan.Methods: The study used individualised data from the recent Afghanistan National Nutrition Survey 2013. Outcome variables were based on growth and weight anthropometry data, which we analysed linearly as Z scores and as dichotomous categories. We analysed data from a total of almost 14 000 index mother–child pairs using Bayesian spatial and generalised least squares regression models accounting for the complex survey design.Findings: We noted that childhood stunting, underweight, and combined stunting and wasting were consistently highest in districts in Farah, Nangarhar, Nuristan, Kunar, Paktia, and Badakhshan provinces. District prevalence ranged from 4% to 84% for childhood stunting and 5% to 66% for underweight. Child wasting exceeded 20% in central and high-conflict regions that bordered Pakistan including east, southeast, and south. Among mothers, dual burden of underweight and overweight or obesity existed in districts of north, northeast, central, and central highlands (prevalence of 15–20%). Linear growth and weight of children were independently associated with household wealth, maternal literacy, maternal anthropometry, child age, food security, geography, and improved hygiene and sanitation conditions. The mother\u27s body-mass index was determined by many of the same factors, in addition to ethnolinguistic status and parity. Younger mothers (old) were more underweight and shorter than older mothers (aged 20–49 years).Interpretation: Afghanistan\u27s rapidly changing political, socioeconomic, and insecurity landscape has both direct and indirect implications on population nutrition. Novel evidence from our study can be used to understand these multifactorial determinants and to identify granular disparities for local level tracking, planning, and implementation of nutritional interventions