Mammography rates for breast cancer screening: a comparison of First Nations women and all other women living in Manitoba, Canada, 1999-2008.

INTRODUCTION: First Nations (FN) women historically have low rates of preventive care, including breast cancer screening. We describe the frequency of breast cancer screening among FN women living in Manitoba and all other Manitoba (AOM) women after the introduction of a provincial, organized breast screening program and explore how age, area of residence, and time period influenced breast cancer screening participation. METHODS: The federal Indian Registry was linked to 2 population-based, provincial data sources. A negative binomial model was used to compare breast cancer screening for FN women with screening for AOM women. RESULTS: From 1999 through 2008, 37% of FN and 59% of AOM women had a mammogram in the previous 2 years. Regardless of area of residence, FN women were less likely to have had a mammogram than AOM women (relative rate [RR] = 0.69 in the north, RR = 0.55 in the rural south, and RR = 0.53 in urban areas). CONCLUSIONS: FN women living in Manitoba had lower mammography rates than AOM women. To ensure equity for all Manitoba women, strategies that encourage FN women to participate in breast cancer screening should be promoted.

Trends in time to diagnosis of colon cancer and impact on clinical outcomes.

BACKGROUND: There has been a rapid increase in screening for colorectal cancer (CRC) over the past several years in North America. This could paradoxically lead to worsening outcomes if the system is not adapted to deal with the increased demand. For example, this could create increased wait times for endoscopy and delayed time to CRC diagnosis, which could worsen clinical outcomes such as stage at diagnosis and/or survival. No previous Canadian study has evaluated the association between time to CRC diagnosis and clinical outcomes. METHODS: The present historical cohort study used Manitoba's population-based cancer registry and Manitoba Health administrative databases. The effect of time to diagnosis on patient survival was evaluated using Cox regression analysis with adjustment for stage at diagnosis, grade of CRC, age, sex, socioeconomic status, comorbidity index score and year of CRC diagnosis. The association between time to diagnosis and CRC stage at diagnosis was evaluated using multivariate logistic regression analysis. RESULTS: The median time to CRC diagnosis increased significantly from 72 days (95% CI 61 days to 83 days) in 2004 to 105 days (95% CI 64 days to 129 days) in the first three months of 2009 (P=0.04). There was no significant association between time to diagnosis and survival. Individuals with the longest time to diagnosis were less likely to have stage III/IV CRC at diagnosis (quartile 4 versus quartile 1: OR 0.50 [95% CI 0.33 to 0.75). CONCLUSION: Time to CRC diagnosis is continuing to increase in Manitoba. Although the present study did not detect a significant negative clinical effect of increasing time to diagnosis, additional studies are required.

A comparative study of robust tests for spread: asymmetric trimming strategies.

We examined 633 procedures that can be used to compare the variability of scores across independent groups. The procedures, except for one, were modifications of the procedures suggested by Levene (1960) and O'Brien (1981). We modified their procedures by substituting robust measures of the typical score and variability, rather than relying on classical estimators. The robust measures that we utilized were either based on a priori or empirically determined symmetric or asymmetric trimming strategies. The Levene-type and O'Brien-type transformed scores were used with either the ANOVA F test, a robust test due to Lee and Fung (1985), or the Welch (1951) test. Based on four measures of robustness, we recommend a Levene-type transformation based upon empirically determined 20% asymmetric trimmed means, involving a particular adaptive estimator, where the transformed scores are then used with the ANOVA F test.

Canadian breast cancer guidelines: have they made a difference?

BACKGROUND: A principal objective of the Canadian Clinical Practice Guidelines for the Care and Treatment of Breast Cancer was to reduce the variation in the way that breast cancer was being treated. To evaluate whether this goal has been reached, we examined variations among surgeons for 4 measures of surgical care and tested for differences in province-wide rates and in variations among surgeons before and after the guidelines were released. METHODS: We studied a population-based cohort of 7022 women living in Manitoba in whom breast cancer was diagnosed from 1995 to 2003 inclusive. Demographic, tumour and treatment information was obtained from the Manitoba Cancer Registry. We examined 4 measures of care: breast-conserving surgery, axillary assessment in invasive disease, axillary node dissection in noninvasive disease and the adequacy of axillary node dissection. Generalized linear models were used to test for significant variations in care among surgeons and to test for differences in province-wide rates and variations in these rates among surgeons before and after introduction of the guidelines. RESULTS: We found clinically significant variations in the province-wide rates of all 4 measures examined. These variations were statistically significant for all measures except axillary node dissection in noninvasive disease. No significant differences in either the province-wide rates or in variations in these rates among surgeons before and after introduction of the guidelines were found for any of the measures. INTERPRETATION: Our results suggest that the Canadian breast cancer guidelines are not meeting their stated objective. New strategies for guideline dissemination and implementation may be required.

Adaptive robust estimation and testing.

We examined nine adaptive methods of trimming, that is, methods that empirically determine when data should be trimmed and the amount to be trimmed from the tails of the empirical distribution. Over the 240 empirical values collected for each method investigated, in which we varied the total percentage of data trimmed, sample size, degree of variance heterogeneity, pairing of variances and group sizes, and population shape, one method resulted in exceptionally good control of Type I errors. However, under less extreme cases of non-normality and variance heterogeneity a number of methods exhibited reasonably good Type I error control. With regard to the power to detect non-null treatment effects, we found that the choice among the methods depended on the degree of non-normality and variance heterogeneity. Recommendations are offered.

Comparing measures of the 'typical' score across treatment groups.

Researchers can adopt one of many different measures of central tendency to examine the effect of a treatment variable across groups. These include least squares means, trimmed means, M-estimators and medians. In addition, some methods begin with a preliminary test to determine the shapes of distributions before adopting a particular estimator of the typical score. We compared a number of recently developed adaptive robust methods with respect to their ability to control Type I error and their sensitivity to detect differences between the groups when data were non-normal and heterogeneous, and the design was unbalanced. In particular, two new approaches to comparing the typical score across treatment groups, due to Babu, Padmanabhan, and Puri, were compared to two new methods presented by Wilcox and by Keselman, Wilcox, Othman, and Fradette. The procedures examined generally resulted in good Type I error control and therefore, on the basis of this critetion, it would be difficult to recommend one method over the other. However, the power results clearly favour one of the methods presented by Wilcox and Keselman; indeed, in the vast majority of the cases investigated, this most favoured approach had substantially larger power values than the other procedures, particularly when there were more than two treatment groups.

Factors associated with physical activity among Canadian high school students.

OBJECTIVES: Identifying multi-level factors affecting physical activity (PA) levels among adolescents is essential to increasing activity to promote health within this population. This study examines the associations between PA and 11 independent factors among Manitoba high school students. METHODS: The sample included 31,202 grade 9-12 students who completed the Manitoba Youth Health Survey. Associations between PA and independent factors were examined separately and through multivariate regression. Analyses were stratified by gender. RESULTS: Perception of athletic ability, school location, parental encouragement and number of active friends were strong predictors of activity for moderately active and active males and females. Grade was a significant predictor of PA for females at both levels of activity but only significant for males when comparing active to inactive students. Perception of schoolwork and means of transport were minimally associated with PA. CONCLUSIONS: Results highlight the importance of targeting multiple levels of influence to increase PA among youth. Programs should focus on older students, females and those who are inactive or moderately active. In addition, social modeling of PA and increasing self-efficacy around activity should be encouraged.

Long-term outcomes following hepatic resection and radiofrequency ablation of colorectal liver metastases.

Recently some have called for randomized controlled trials comparing RFA to hepatic resection, particularly for patients with only a few small metastases. The objectives were to compare local recurrence and survival following RFA and hepatic resection for colorectal liver metastases. This was a retrospective review of open RFA and hepatic resection for colorectal liver metastases between January 1998 and May 2007. All patients who had RFA were considered to have unresectable disease. 58 patients had hepatic resection and 43 had RFA. A 5-year survival after resection was 43% compared to 23% after RFA. For patients with solitary lesions, a 5-year survival was 48% after resection and 15% after RFA. Sixty percent of patients suffered local recurrences after RFA compared to 7% after hepatic resection. RFA is inferior to resection. The results observed in this study support the consensus that RFA cannot be considered an equivalent procedure to hepatic resection.

The new and improved two-sample T test.

This article considers the problem of comparing two independent groups in terms of some measure of location. It is well known that with Student's two-independent-sample t test, the actual level of significance can be well above or below the nominal level, confidence intervals can have inaccurate probability coverage, and power can be low relative to other methods. A solution to deal with heterogeneity is Welch's (1938) test. Welch's test deals with heteroscedasticity but can have poor power under arbitrarily small departures from normality. Yuen (1974) generalized Welch's test to trimmed means; her method provides improved control over the probability of a Type I error, but problems remain. Transformations for skewness improve matters, but the probability of a Type I error remains unsatisfactory in some situations. We find that a transformation for skewness combined with a bootstrap method improves Type I error control and probability coverage even if sample sizes are small.