OBJECTIVE: Our study objectives were (a) to investigate the heritability of age of menarche in twins, (b) to obtain the association between age of menarche and childhood factors, and reproductive events/behavior, (c) to examine whether or not having a male co-twin affects early/late menarche.
METHODOLOGY: A group of female-female identical (n = 108, 54 pairs), non-identical twins (n = 68, 34 pairs) and 17 females from opposite-sex twin sets were identified from twin registries of Malaysia and Iran. Genetic analysis was performed via two methods of Falconers' formula and maximum likelihood.
RESULTS: Heritability was found to be 66% using Falconers' formula and 15% using univariate twin analysis. Model analysis revealed that shared environmental factors have a major contribution in determining the age of menarche (82%) followed by non-shared environment (18%).
DISCUSSION: Result of this study is consistent with that of the literature. Timing of menarche could be under the influence of shared and non-shared environmental effects. Hirsutism was found to have a higher frequency among subjects with late menarche. There was no significant difference in age of menarche between females of opposite-sex twins and females of same-sex twins.
CONCLUSION: It is concluded that twin models provide a powerful means of examining the total genetic contribution to age of menarche. Longitudinal studies of twins may clarify the type of environmental effects that determine the age of menarche.
METHODS: A total of 250 children (9-12 years of age) and their parents participated in this cross-sectional study. Physical Activity Questionnaire for Older Children and Neighbourhood Environmental Walkability Scale as well as questions on constrained behaviours (avoidance and defensive behaviours) were used to assess the children's physical activity and parental perception of neighbourhood environment and safety, respectively.
RESULTS: More than one-third (36.0%) of the children were physically inactive compared with only a small percentage (4.8%) who were physically active, with boys achieving higher physical activity levels than girls (t = 2.564, P = 0.011). For the environmental scale, parents' perception of land-use mix (access) (r = 0.173, P = 0.006), traffic hazards (r = -0.152, P = 0.016) and defensive behaviour (r = -0.024, P = 0.143) correlated significantly with children's physical activity. In multiple linear regression analysis, child's gender (β = -0.226; P = 0.003), parent's education (β = 0.140; P = 0.001), household income (β = 0.151; P = 0.024), land-use mix (access) (β = 0.134; P = 0.011) and defensive behaviour (β = -0.017; P = 0.038) were significantly associated with physical activity in children (R = 0.349, F = 6.760; P
METHOD: This paper aims to develop a sustainable pedestrian gap crossing index model based on traffic flow density. It focusses on the gaps accepted by pedestrians and their decision for street crossing, where (Log-Gap) logarithm of accepted gaps was used to optimize the result of a model for gap crossing behavior. Through a review of extant literature, 15 influential variables were extracted for further empirical analysis. Subsequently, data from the observation at an uncontrolled mid-block in Jalan Ampang in Kuala Lumpur, Malaysia was gathered and Multiple Linear Regression (MLR) and Binary Logit Model (BLM) techniques were employed to analyze the results.
RESULTS AND CONCLUSIONS: From the results, different pedestrian behavioral characteristics were considered for a minimum gap size model, out of which only a few (four) variables could explain the pedestrian road crossing behavior while the remaining variables have an insignificant effect. Among the different variables, age, rolling gap, vehicle type, and crossing were the most influential variables. The study concludes that pedestrians' decision to cross the street depends on the pedestrian age, rolling gap, vehicle type, and size of traffic gap before crossing.
PRACTICAL APPLICATIONS: The inferences from these models will be useful to increase pedestrian safety and performance evaluation of uncontrolled midblock road crossings in developing countries.