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Biomedical subjects

Martin C Gulliford

Publications and source records attributed to Martin C Gulliford.

At least 19 recordsLinked to original sources
PubMed2007

A simulation study of odds ratio estimation for binary outcomes from cluster randomized trials.

We used simulation to compare accuracy of estimation and confidence interval coverage of several methods for analysing binary outcomes from cluster randomized trials. The following methods were used to estimate the population-averaged intervention effect on the log-odds scale: marginal logistic regression models using generalized estimating equations with information sandwich estimates of standard error (GEE); unweighted cluster-level mean difference (CL/U); weighted cluster-level mean difference (CL/W) and cluster-level random effects linear regression (CL/RE). Methods were compared across trials simulated with different numbers of clusters per trial arm, numbers of subjects per cluster, intraclass correlation coefficients (rho), and intervention versus control arm proportions. Two thousand data sets were generated for each combination of design parameter values. The results showed that the GEE method has generally acceptable properties, including close to nominal levels of confidence interval coverage, when a simple adjustment is made for data with relatively few clusters. CL/U and CL/W have good properties for trials where the number of subjects per cluster is sufficiently large and rho is sufficiently small. CL/RE also has good properties in this situation provided a t-distribution multiplier is used for confidence interval calculation in studies with small numbers of clusters. For studies where the number of subjects per cluster is small and rho is large all cluster-level methods may perform poorly for studies with between 10 and 50 clusters per trial arm.

Algorithms↗
PubMed2006

Heritabilities and shared environmental effects were estimated from household clustering in national health survey data.

OBJECTIVES: The relative contributions of genetic and environmental variables to within-household clustering of quantitative traits in household surveys are poorly characterized. We estimated shared genetic and shared environmental contributions to within-household correlation for anthropometric variables and cardiovascular disease risk factors. STUDY DESIGN AND SETTING: Data were analyzed for the Health Survey for England 1998, a representative national household survey. Two-generation pedigrees were defined using information for relationships within households. After standardizing for age and sex, data were analyzed for 11 quantitative traits. Variance components models were fitted to estimate the proportion of variance due to additive genetic variance or shared environmental effects. RESULTS: Within-household correlation coefficients for all related and unrelated subjects ranged from 0.10 for C-reactive protein to 0.31 for height. Pairwise correlations between related individuals within households were consistently higher than those between unrelated individuals. Estimated heritability ranged from 6% for diastolic blood pressure to 40% for serum cholesterol. The proportion of variance attributable to shared environmental effects ranged from 8% for cholesterol to 24% for height. CONCLUSION: In this large, representative national sample of generally small families, estimates for heritability were generally lower than previously reported, whereas the contribution of shared environment and individual-level variation were greater.

Anthropometry↗
PubMed2006

No association between immunization and Guillain-Barré syndrome in the United Kingdom, 1992 to 2000.

BACKGROUND: Our goal was to determine whether immunization is associated with the incidence of Guillain-Barré syndrome (GBS). METHODS: We analyzed data for all patients registered with 253 general practices in the United Kingdom General Practice Research Database from 1992 to 2000, with a mean of 1.8 million registered patients. We identified new occurrences of GBS and estimated age- and sex-specific and age-standardized incidence rates. We then determined whether the date of diagnosis was made within 42 days of any immunization and estimated the relative risk of diagnosis following immunization after adjusting for age and sex. RESULTS: There were 228 incident cases of GBS, including 107 women and 121 men. The age-standardized incidence rate per 100 000 person-years was 1.22 (95% confidence interval [CI], 0.98-1.46) in women and 1.45 (95% CI, 1.19-1.72) in men. Age-specific incidence rates per 100 000 person-years were highest in men aged 65 to 74 years (3.86; 95% CI, 2.50-5.70) and women aged 75 to 84 years (2.54; 95% CI, 1.39-4.27). There were 7 cases (3.1%) in which the onset occurred within 42 days of any immunization; 3 of the 7 cases occurred after influenza immunization. There were 221 cases (97.0%) that were not associated with immunization. The adjusted relative risk during the 42 days after immunization was 1.03 (95% CI, 0.48-2.18; P = .94). CONCLUSIONS: There is either minimal or no risk of GBS associated with routine immunization practice in the United Kingdom. Obtaining a precise estimate of any potential risk associated with an individual vaccine would require a study with more GBS cases.

Adolescent↗
PubMed2006

The 18 Household Food Security Survey items provide valid food security classifications for adults and children in the Caribbean.

BACKGROUND: We tested the properties of the 18 Household Food Security Survey (HFSS) items, and the validity of the resulting food security classifications, in an English-speaking middle-income country. METHODS: Survey of primary school children in Trinidad and Tobago. Parents completed the HFSS. Responses were analysed for the 10 adult-referenced items and the eight child-referenced items. Item response theory models were fitted. Item calibrations and subject scores from a one-parameter logistic (1PL) model were compared with those from either two-parameter logistic model (2PL) or a model for differential item functioning (DIF) by ethnicity. RESULTS: There were 5219 eligible with 3858 (74%) completing at least one food security item. Adult item calibrations (standard error) in the 1PL model ranged from -4.082 (0.019) for the 'worried food would run out' item to 3.023 (0.042) for 'adults often do not eat for a whole day'. Child item calibrations ranged from -3.715 (0.025) for 'relied on a few kinds of low cost food' to 3.088 (0.039) for 'child didn't eat for a whole day'. Fitting either a 2PL model, which allowed discrimination parameters to vary between items, or a differential item functioning model, which allowed item calibrations to vary between ethnic groups, had little influence on interpretation. The classification based on the adult-referenced items showed that there were 19% of respondents who were food insecure without hunger, 10% food insecure with moderate hunger and 6% food insecure with severe hunger. The classification based on the child-referenced items showed that there were 23% of children who were food insecure without hunger and 9% food insecure with hunger. In both children and adults food insecurity showed a strong, graded association with lower monthly household income (P < 0.001). CONCLUSION: These results support the use of 18 HFSS items to classify food security status of adults or children in an English-speaking country where food insecurity and hunger are more frequent overall than in the US.

Adolescent↗
PubMed2006

Food insecurity, weight control practices and body mass index in adolescents.

OBJECTIVE: We investigated whether experienced food insecurity was associated with weight control behaviour of adolescents. DESIGN: A national survey of 16-year-old students with the six-item food security scale, questions concerning intentions of trying to change weight, physical activity patterns, and measurement of height and weight. SETTING: Representative sample of 29 schools in Trinidad, West Indies. SUBJECTS: Data analysed for 1903 subjects including 1484 who were food-secure and 419 who were food-insecure. RESULTS: In the whole sample, food security status did not vary by body mass index (BMI) category. 'Trying to gain weight' and 'spending most free time in activities involving little physical effort' were each associated with lower BMI. 'Trying to gain weight' was more frequent in food-insecure subjects (135, 32%) than in food-secure subjects (369, 25%, P = 0.012). After adjustment for BMI, age, sex, ethnicity and socio-economic variables, the adjusted odds ratio (OR) of 'trying to gain weight' for food-insecure subjects was 1.39 (95% confidence interval (CI) 1.07-1.82, P = 0.014). Food-insecure subjects (197, 47%) were more likely than food-secure subjects (575, 39%) to report that most of their free time was spent doing things that involved little physical effort (P = 0.003). This association was not explained by adjustment for BMI, age, sex and ethnicity (OR = 1.41, 95% CI 1.13-1.76, P = 0.002) or additional socio-economic variables (OR = 1.27, 95% CI 1.02-1.57, P = 0.033). CONCLUSIONS: Adolescents who experience food insecurity are more likely to intend to gain weight but engage in less physical activity than food-secure subjects with the same BMI.

Adolescent↗
PubMed2006

Explaining inequalities in access to treatment in lung cancer.

BACKGROUND: Geographical inequalities in lung cancer treatment and patient survival have been described. We hypothesized that lung cancer patients' access to treatment may be influenced by deprivation and the pathway to care. METHODS: Case notes were reviewed for patients resident in south-east London who were registered with lung cancer at the Thames Cancer Registry in 1998. Use of surgery, chemotherapy, radiotherapy or any specific treatment and one-year survival were examined. Analyses were adjusted for age, sex, histology, stage and basis of diagnosis. RESULTS: Data for 695 out of 958 (73%) patients were analysed. Subjects who were initially referred to a specialist in thoracic medicine, surgery or oncology were more likely to receive active treatment (71%) than subjects who were referred to other consultants (51%) or who were admitted as emergencies (42%) (P < 0.0001). CONCLUSION: Socio-economic deprivation was associated with lower rates of treatment and this partly explained variations in survival. Subjects who were referred to specialists were more likely to receive active treatment and treatment patterns varied between first trust attended.

Aged↗
PubMed2006

Sharing specialist skills for diabetes in an inner city: a comparison of two primary care organisations over 4 years.

OBJECTIVE: To evaluate the effects of organizational change and sharing of specialist skills and information technology for diabetes in two primary care groups (PCGs) over 4 years. METHODS: In PCG-A, an intervention comprised dedicated specialist sessions in primary care, clinical guidelines, educational meetings for professionals and a shared diabetes electronic patient record (EPR). Comparison was made with the neighbouring PCG-B as control. In intervention and control PCGs, practice development work was undertaken for a new contract for family doctors. Data were collected for clinical measures, practice organizational characteristics and professional and patient views. RESULTS: Data were analysed for 26 general practices including 17 in PCG-A and nine in PCG-B. The median practice-specific proportions of patients with HbA1c recorded annually increased in both areas: PCG-A from median 65% to 77%, while PCG-B from 53% to 84%. For cholesterol recording, PCG-A increased from 50% to 76%, and PCG-B from 56% to 80%. Organizational changes in both PCGs included the establishment of recall systems, dedicated clinics and educational sessions for patients. In both PCGs, practices performing poorly at baseline showed the greatest improvements in organization and clinical practice. Primary care professionals' satisfaction with access and communication with diabetes specialist doctors and nurses increased, more so in the intervention PCG. Only 16% of primary care professional respondents used the diabetes EPR at least monthly. Patient satisfaction and knowledge did not change. CONCLUSIONS: Improvements in practices' organizational arrangements were associated with improvements in clinical care in both PCGs. Sharing specialist skills in one PCG was associated with increased professional satisfaction but no net improvement in clinical measures. A shared diabetes EPR is unlikely to be used, unless integrated with practice information systems.

Diabetes Mellitus↗
PubMed2005

Self-administration of a food security scale by adolescents: item functioning, socio-economic position and food intakes.

OBJECTIVE: To evaluate the reliability and validity of a six-item food security scale when self-administered by adolescents. DESIGN: Cross-sectional questionnaire survey including the six-item food security measure, socio-economic variables and a food-frequency questionnaire. SETTING: Representative sample of 29 schools in Trinidad. SUBJECTS: In total 1903 students aged approximately 16 years. RESULTS: Item affirmatives ranged from 514 (27%) for the 'balanced meal' item to 128 (7%) for the 'skipped or cut meals often' item and 141 (7%) for the 'hungry' item. Item-score correlations ranged from 0.444 to 0.580. Cronbach's alpha was 0.77. Relative item severities from the Rasch model ranged from -1.622 (standard error 0.043) for the 'balanced meal' item to 1.103 (0.068) for the 'skipped or cut meals often' item and 0.944 (0.062) for the 'hungry' item. The 'hungry' item gave a slightly lower relative severity in boys than girls. Food insecurity was associated with household overcrowding (adjusted odds ratio comparing highest and lowest quartiles 2.61, 95% confidence interval 1.75 to 3.91), lack of pipe-borne water in the home, low paternal education or paternal unemployment. After adjusting for socio-economic variables, food insecurity was associated with less frequent consumption of fruit (0.75, 0.60 to 0.94) or fish (0.72, 0.58 to 0.88) but more frequent consumption of biscuits or cakes (1.47, 1.02 to 2.11). CONCLUSIONS: The food security scale provides a valid, reliable measure in adolescents, although young people report being hungry but not eating relatively more frequently than adults. Food-insecure adolescents have low socio-economic position and may eat less healthy diets.

Adolescent↗
PubMed2005

Increased utilization of primary care 5 years before diagnosis of type 2 diabetes: a matched cohort study.

OBJECTIVE: To determine whether case subjects who were later diagnosed with type 2 diabetes utilized primary care differently from control subjects who remained free from diabetes. RESEARCH DESIGN AND METHODS: We conducted a matched cohort study using the U.K. General Practice Research Database. Case subjects were aged 30-89 years, diagnosed with diabetes, and later prescribed oral hypoglycemic drugs between 1997 and 2000. Control subjects, who were matched for age, sex, and general practice, were not diagnosed with diabetes and not treated with oral hypoglycemic drugs or insulin. RESULTS: Data were analyzed for 5,158 case subjects (2,492 women and 2,666 men) and their matched control subjects with a mean age of 63 years. Five years before the date of diagnosis, case subjects consulted more frequently than control subjects (rate ratio [RR] 1.26 [95% CI 1.20-1.33]) and received more prescription items (1.44 [1.36-1.53]). Consultations were increased for a wide range of conditions. The cumulative 5-year prevalence of diagnoses of hypertension or treatment, hyperlipidemia or treatment, obesity, or coronary heart disease or stroke was 66.1% in case subjects and 45.9% in control subjects (1.44 [1.40-1.49]). A medical diagnosis of hyperglycemia or impaired glucose tolerance was highly (>99%) specific for later diagnosis of diabetes. CONCLUSIONS: Primary care consultations and drug utilization are increased from 5 years before diagnosis of diabetes. Diagnoses of hypertension, hyperlipidemia, obesity, or coronary heart disease or stroke have moderate sensitivity for subsequent diabetes but are nonspecific. A diagnosis of hyperglycemia has a high specificity for later detection of diabetes.

Cohort Studies↗
PubMed2004

Reliability and validity of a short form household food security scale in a Caribbean community.

BACKGROUND: We evaluated the reliability and validity of the short form household food security scale in a different setting from the one in which it was developed. METHODS: The scale was interview administered to 531 subjects from 286 households in north central Trinidad in Trinidad and Tobago, West Indies. We evaluated the six items by fitting item response theory models to estimate item thresholds, estimating agreement among respondents in the same households and estimating the slope index of income-related inequality (SII) after adjusting for age, sex and ethnicity. RESULTS: Item-score correlations ranged from 0.52 to 0.79 and Cronbach's alpha was 0.87. Item responses gave within-household correlation coefficients ranging from 0.70 to 0.78. Estimated item thresholds (standard errors) from the Rasch model ranged from -2.027 (0.063) for the 'balanced meal' item to 2.251 (0.116) for the 'hungry' item. The 'balanced meal' item had the lowest threshold in each ethnic group even though there was evidence of differential functioning for this item by ethnicity. Relative thresholds of other items were generally consistent with US data. Estimation of the SII, comparing those at the bottom with those at the top of the income scale, gave relative odds for an affirmative response of 3.77 (95% confidence interval 1.40 to 10.2) for the lowest severity item, and 20.8 (2.67 to 162.5) for highest severity item. Food insecurity was associated with reduced consumption of green vegetables after additionally adjusting for income and education (0.52, 0.28 to 0.96). CONCLUSIONS: The household food security scale gives reliable and valid responses in this setting. Differing relative item thresholds compared with US data do not require alteration to the cut-points for classification of 'food insecurity without hunger' or 'food insecurity with hunger'. The data provide further evidence that re-evaluation of the 'balanced meal' item is required.

Adult↗
PubMed2004

Availability and structure of primary medical care services and population health and health care indicators in England.

BACKGROUND: It has been proposed that greater availability of primary medical care practitioners (GPs) contributes to better population health. We evaluated whether measures of the supply and structure of primary medical services are associated with health and health care indicators after adjusting for confounding. METHODS: Data for the supply and structure of primary medical services and the characteristics of registered patients were analysed for 99 health authorities in England in 1999. Health and health care indicators as dependent variables included standardised mortality ratios (SMR), standardised hospital admission rates, and conceptions under the age of 18 years. Linear regression analyses were adjusted for Townsend score, proportion of ethnic minorities and proportion of social class IV/ V. RESULTS: Higher proportions of registered rural patients and patients >/= 75 years were associated with lower Townsend deprivation scores, with larger partnership sizes and with better health outcomes. A unit increase in partnership size was associated with a 4.2 (95% confidence interval 1.7 to 6.7) unit decrease in SMR for all-cause mortality at 15-64 years (P = 0.001). A 10% increase in single-handed practices was associated with a 1.5 (0.2 to 2.9) unit increase in SMR (P = 0.027). After additional adjustment for percent of rural and elderly patients, partnership size and proportion of single-handed practices, GP supply was not associated with SMR (-2.8, -6.9 to 1.3, P = 0.183). CONCLUSIONS: After adjusting for confounding with health needs of populations, mortality is weakly associated with the degree of organisation of practices as represented by the partnership size but not with the supply of GPs.

Adolescent↗
PubMed2004

Patterns of intra-cluster correlation from primary care research to inform study design and analysis.

OBJECTIVE: To provide information concerning the magnitude of the intraclass correlation coefficient (ICC) for cluster-based studies set in primary care. STUDY DESIGN AND SETTING: Reanalysis of data from 31 cluster-based studies in primary care to estimate intraclass correlation coefficients from random effects models using maximum likelihood estimation. RESULTS: ICCs were estimated for 1,039 variables. The median ICC was 0.010 (interquartile range [IQR] 0 to 0.032, range 0 to 0.840). After adjusting for individual- and cluster-level characteristics, the median ICC was 0.005 (IQR 0 to 0.021). A given measure showed widely varying ICC estimates in different datasets. In six datasets, the ICCs for SF-36 physical functioning scale ranged from 0.001 to 0.055 and for SF-36 general health from 0 to 0.072. In four datasets, the ICC for systolic blood pressure ranged from 0 to 0.052 and for diastolic blood pressure from 0 to 0.108. CONCLUSION: The precise magnitude of between-cluster variation for a given measure can rarely be estimated in advance. Studies should be designed with reference to the overall distribution of ICCs and with attention to features that increase efficiency.

Cluster Analysis↗
PubMed2003

Non-parametric bootstrap confidence intervals for the intraclass correlation coefficient.

The intraclass correlation coefficient rho plays a key role in the design of cluster randomized trials. Estimates of rho obtained from previous cluster trials and used to inform sample size calculation in planned trials may be imprecise due to the typically small numbers of clusters in such studies. It may be useful to quantify this imprecision. This study used simulation to compare different methods for assigning bootstrap confidence intervals to rho for continuous outcomes from a balanced design. Data were simulated for combinations of numbers of clusters (10, 30, 50), intraclass correlation coefficients (0.001, 0.01, 0.05, 0.3) and outcome distributions (normal, non-normal continuous). The basic, bootstrap-t, percentile, bias corrected and bias corrected accelerated bootstrap intervals were compared with new methods using the basic and bootstrap-t intervals applied to a variance stabilizing transformation of rho. The standard bootstrap methods provided coverage levels for 95 per cent intervals that were markedly lower than the nominal level for data sets with only 10 clusters, and only provided close to 95 per cent coverage when there were 50 clusters. Application of the bootstrap-t method to the variance stabilizing transformation of rho improved upon the performance of the standard bootstrap methods, providing close to nominal coverage.

Cluster Analysis↗
PubMed2003

Evaluation of equity in diabetes health care in relation to African and Caribbean ethnicity.

OBJECTIVE: Many US studies have shown that ethnic minority groups have less access to health care. We evaluated whether black African and black Caribbean people with diabetes in the UK gain access to diabetes health care on an equitable basis compared with white people. DESIGN: Cross-sectional questionnaire survey set in 29 general practices in south London. Main measures were self-reported morbidity, SF-36 scores and utilisation of health care. Analyses of utilisation variables were adjusted for age, sex, ethnic group, duration of diabetes, and socio-economic and health status. RESULTS: There were 1,899 respondents (64%) from 2,983 individuals registered with diabetes. These included 799 white, 522 black Caribbean, 163 black African and 415 other subjects with type 2 diabetes. After adjusting for need, black Caribbeans reported higher utilisation of health care than white subjects for four of nine utilisation variables, and black Africans for two. For the remaining variables utilisation was equivalent in different ethnic groups. Black Caribbean subjects were more likely to be treated for hypertension if hypertensive (odds ratio 1.84, 95% CI 1.05 to 3.22), to use blood or urine self-monitoring (1.40, 1.04 to 1.88) and to have attended a diabetes nurse (1.34, 1.04 to 1.74) or dietician (1.49, 1.19 to 1.86). Black Africans were more likely to have attended a dietician (2.15, 1.40 to 3.29) or an ophthalmologist (1.72, 1.10 to 2.70) in the past year. CONCLUSION: There was no evidence from this study that black African or black Caribbean subjects had less access to diabetes health care in relation to need.

Adult↗
PubMed2003

Food insecurity, food choices, and body mass index in adults: nutrition transition in Trinidad and Tobago.

BACKGROUND: This study evaluated whether food insecurity and obesity were associated in a population sample in Trinidad. METHODS: A sample was drawn of 15 clusters of households, in north central Trinidad. Resident adults were enumerated. A questionnaire was administered including the short form Household Food Security Scale (HFSS). Heights and weights were measured. Analyses were adjusted for age, sex, and ethnic group. RESULTS: Data were analysed for 531/631 (84%) of eligible respondents including 241 men and 290 women with a mean age of 47 (range 24-89) years. Overall, 134 (25%) of subjects were classified as food insecure. Food insecurity was associated with lower household incomes and physical disability. Food insecure subjects were less likely to eat fruit (food insecure 40%, food secure 55%; adjusted odds ratio [OR] = 0.60, 95% CI: 0.36-0.99, P = 0.045) or green vegetables or salads (food insecure 28%, food secure 51%; adjusted OR = 0.46, 95% CI: 0.27-0.79, P = 0.005) on >/=5-6 days per week. Body mass index (BMI) was available for 467 (74%) subjects of whom 41 (9%) had BMI <20 kg/m(2), 157 (34%) had BMI 25-29 kg/m(2), and 120 (26%) had BMI >/=30 kg/m(2). Underweight (OR = 3.21, 95% CI: 1.17-8.81) was associated with food insecurity, but obesity was not (OR = 1.08, 95% CI: 0.55-2.12). CONCLUSIONS: Food insecurity was frequent at all levels of BMI and was associated with lower consumption of fruit and vegetables. Food insecurity was associated with underweight but not with present obesity.

Adult↗
PubMed2003

Food insecurity and low income in an English inner city.

BACKGROUND: Low incomes may not provide the minimum requirements for healthy living. We evaluated experiences of food insecurity in relation to income in inner London. METHODS: Subjects attending 10 general medical practices completed a short self-administered questionnaire, including the short form Household Food Security Scale and a short food frequency questionnaire. RESULTS: Responses were obtained from 431/495 (87 per cent) subjects. Overall 87 (20 per cent) of subjects were classified as food insecure. Food insecurity was negatively associated with household income (p = 0.004). University-educated subjects (8 per cent) were less often food insecure than all others (26 per cent). Subjects who were food insecure were less likely to report eating fruit daily (food secure 48 per cent, food insecure 33 per cent, p = 0.017) or vegetables or salads daily (food secure 56 per cent, food insecure 34 per cent, p = 0.002). CONCLUSIONS: Experiences of food insecurity may be common in households with incomes at the level of the UK national minimum wage or lower.

Adolescent↗