Sample Size Calculation for Estimating or Testing a Nonzero Squared Multiple Correlation Coefficient

Ethnicity differences in geometric remodelling and myocardial composition in hypertension unveiled by cardiovascular magnetic resonance

AIMS

Hypertensive patients of African ancestry (Afr-a) have higher incidences of heart failure and worse clinical outcomes than hypertensive patients of European ancestry (Eu-a), yet the underlying mechanisms remain misunderstood. This study investigated right (RV) and left (LV) ventricular remodelling alongside myocardial tissue derangements between Afr-a and Eu-a hypertensives.

METHODS AND RESULTS

63 Afr-a and 47 Eu-a hypertensives underwent multi-parametric cardiovascular magnetic resonance. Biventricular volumes, mass, function, mass/end-diastolic volume (M/V) ratios, T2 and pre-/post-contrast T1 relaxation times, synthetic extracellular volume, and myocardial fibrosis (MF) were measured. 3D shape modelling was implemented to delineate ventricular geometry. LV and RV mass (indexed to body-surface-area) and M/V ratio were significantly greater in Afr-a than Eu-a hypertensives (67.1 ± 21.7 vs. 58.3 ± 16.7 g/m2, 12.6 ± 3.48 vs. 10.7 ± 2.71 g/m2, 0.79 ± 0.21 vs. 0.70 ± 0.14 g/mL, and 0.16 ± 0.04 vs. 0.13 ± 0.03 g/mL, respectively; P < 0.03). Afr-a patients showed greater basal interventricular septum thickness than Eu-a patients, influencing LV hypertrophy and RV cavity changes. This biventricular remodelling was associated with prolonged T2 relaxation time (47.0 ± 2.2 vs. 45.7 ± 2.2 ms, P = 0.005) and higher prevalence (23% vs. 4%, P = 0.001) and extent of MF [2.3 (0.6-14.3) vs. 1.6 (0.9-2.5) % LV mass, P = 0.008] in Afr-a patients. Multivariable linear regression showed that modifiable cardiovascular risk factors and greater end-diastolic volume, but not ethnicity, were independently associated with greater LV mass.

CONCLUSION

Afr-a hypertensives had distinctive biventricular remodelling, including increased RV mass, septal thickening and myocardial tissue abnormalities compared with Eu-a hypertensives. From this study, modifiable cardiovascular risk factors and ventricular geometry, but not ethnicity, were independently associated with greater LV myocardial mass.

Reallocation of time between preschoolers' 24-h movement behaviours and executive functions: A compositional data analysis

The objectives of the survey were to explored the associations of the 24-h movement behaviours (MB) with executive functions (EFs) and quantified the predicted changes in EFs following allocation of time among behaviours. In the cross-sectional survey, 135 preschoolers (3 ~ 5 years) were enrolled. Physical activity (PA) and sedentary (SED) time were objectively measured employing an ActiGraph GT9X. Sleep time was reported by parents. EFs were assessed using the iPad-based Early Years Toolbox which is a collection of computerized tasks consisting of brief tasks assessed from games administered and scored according to protocol. To explore the associations of the 24-h MB with EFs, compositional multiple linear regression was employed. To quantify the predicted changes in EFs following allocation of time among behaviours, compositional isotemporal substitution was used. Moderate-to-vigorous physical activity (MVPA) was positively related to cognitive flexibility. Replacing sleep or SED with MVPA was associated with positive changes in cognitive flexibility. When MVPA was replaced with sleep or SED, the predicted detriments to cognitive flexibility were larger than predicted benefits of replacing sleep or SED with MVPA. The findings highlight the key role of intensity of PA for preschoolers' EFs and the importance of meeting recommended levels of MVPA.

Sample Size Calculations in Simple Linear Regression: A New Approach

The problem tackled is the determination of sample size for a given level and power in the context of a simple linear regression model. The standard approach deals with planned experiments in which the predictor X is observed for a number n of times and the corresponding observations on the response variable Y are to be drawn. The statistic that is used is built on the least squares' estimator of the slope parameter. Its conditional distribution given the data on the predictor X is utilized for sample size calculations. This is problematic. The sample size n is already presaged and the data on X is fixed. In unplanned experiments, in which both X and Y are to be sampled simultaneously, we do not have data on the predictor X yet. This conundrum has been discussed in several papers and books with no solution proposed. We overcome the problem by determining the exact unconditional distribution of the test statistic in the unplanned case. We have provided tables of critical values for given levels of significance following the exact distribution. In addition, we show that the distribution of the test statistic depends only on the effect size, which is defined precisely in the paper.

Effects of self-disclosure and resilience on reproductive concern in patients of childbearing age with breast cancer: a cross-sectional survey study

OBJECTIVES

To assess reproductive concerns in patients of childbearing age with breast cancer and examine the relationship between self-disclosure, resilience and reproductive concerns.

DESIGN

Cross-sectional survey.

SETTING

Five tertiary first-class general hospitals in Sichuan Province, Southwest China.

PARTICIPANTS

A total of 319 patients with breast cancer of reproductive age who were hospitalised in the breast oncology department participated in this study.

MAIN OUTCOME MEASURES

Primary outcomes were the relationship between resilience, self-disclosure and reproductive concerns, and mediating effect analyses. Secondary outcomes included the status of reproductive concerns.

RESULTS

The model accounted for 39.1% of the variance in reproductive concerns. Self-disclosure had a direct negative effect on reproductive concerns (β= -0.371, p=0.001). Resilience had a direct negative effect on reproductive concerns (β= -0.349, p=0.001) and a direct positive effect on self-disclosure (β=0.507, p=0.001). Furthermore, self-disclosure partially mediated the relation between resilience and reproductive concerns (β= -0.177; SE=0.041; 95% CI -0.261 to -0.104; p<0.050), with a bootstrap of 10 000 samples.

CONCLUSIONS

The findings suggest that self-disclosure and resilience may ease reproductive concern. Therefore, self-disclosure education and resilience-oriented interventions should be provided to patients of childbearing age with breast cancer, to reduce reproductive concerns.

Sample size calculations for model validation in linear regression analysis

Background

Linear regression analysis is a widely used statistical technique in practical applications. For planning and appraising validation studies of simple linear regression, an approximate sample size formula has been proposed for the joint test of intercept and slope coefficients.

Methods

The purpose of this article is to reveal the potential drawback of the existing approximation and to provide an alternative and exact solution of power and sample size calculations for model validation in linear regression analysis.

Results

A fetal weight example is included to illustrate the underlying discrepancy between the exact and approximate methods. Moreover, extensive numerical assessments were conducted to examine the relative performance of the two distinct procedures.

Conclusions

The results show that the exact approach has a distinct advantage over the current method with greater accuracy and high robustness.

Electronic supplementary material

The online version of this article (10.1186/s12874-019-0697-9) contains supplementary material, which is available to authorized users.