Quantifying heteroskedasticity using slope of local variances index

In econometrics, heteroskedasticity refers to the case when the variances of the error terms of the data in hand are not equal. Heteroskedastic time series are challenging to different forecasting models. However, all available solutions adopt the strategy of accommodating heteroskedasticity in the time series and consider it as a type of noise. Some statistical tests were developed over the past three decades to determine whether a time series features heteroskedastic behaviour. This paper presents a novel strategy to handle this problem by deriving a quantifying measure for heteroskedasticity. The proposed measure relies on the definition of heteroskedasticity as a time-variant variance in the time series. In this work, heteroskedasticity is measured by calculating local variances using linear filters, estimating variance trends, calculating changes in variance slopes, and finally obtaining the average slope angle. The results confirm that the proposed index complies with the widely popular heteroskedasticity tests.

Associations between child temperament, maternal feeding practices and child body mass index during the preschool years: a systematic review of the literature

It is a research priority to identify modifiable risk factors to improve the effec- tiveness of childhood obesity prevention strategies. Research, however, has largely overlooked the role of child temperament and personality implicated in obesogenic risk factors such as maternal feeding and body mass index (BMI) of preschoolers. A systematic review of relevant literature was conducted to inves- tigate the associations between child temperament, child personality, maternal feeding and BMI and/or weight gain in infants and preschoolers; 18 papers were included in the review. The findings revealed an association between the temperament traits of poor self-regulation, distress to limitations, low and high soothability, low negative affectivity and higher BMI in infants and preschool- aged children. Temperament traits difficult, distress to limitations, surgency/ extraversion and emotionality were significantly associated with weight gain rates in infants. The results also suggested that child temperament was associated with maternal feeding behaviours that have been shown to influence childhood over- weight and obesity, such as using restrictive feeding practices with children per- ceived as having poor self-regulation and feeding potentially obesogenic food and drinks to infants who are more externalizing. Interestingly, no studies to date have evaluated the association between child personality and BMI/weight gain in infants and preschoolers. There is a clear need for further research into the association of child temperament and obesogenic risk factors in preschool-aged children.