The Richit-Richards family of distributions and its use in forestry

Johnson's SB and the logit-logistic are four-parameter distribution models that may be obtained from the standard normal and logistic distributions by a four-parameter transformation. For relatively small data sets, such as diameter at breast height measurements obtained from typical sample plots, distribution models with four or less parameters have been found to be empirically adequate. However, in situations in which the distributions are complex, for example in mixed stands or when the stand has been thinned or when working with aggregated data, then distribution models with more shape parameters may prove to be necessary. By replacing the symmetric standard logistic distribution of the logit-logistic with a one-parameter “standard Richards” distribution and transforming by a five-parameter Richards function, we obtain a new six-parameter distribution model, the “Richit-Richards”. The Richit-Richards includes the “logit-Richards”, the “Richit-logistic”, and the logit-logistic as submodels. Maximum likelihood estimation is used to fit the model, and some problems in the maximum likelihood estimation of bounding parameters are discussed. An empirical case study of the Richit-Richards and its submodels is conducted on pooled diameter at breast height data from 107 sample plots of Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.). It is found that the new models provide significantly better fits than the four-parameter logit-logistic for large data sets.

Social and demographic factors of young fathers in the UK and USA

Research on disadvantaged young fathers has been minimally addressed in the literature, particularly in the UK. In both countries teenage pregnancy rates are high and costly in terms of social policy and community provision. This paper explores 2 studies involving 24 young men with an average age of 17 on the transition to young fatherhood; one study was conducted in the UK with white young men and the other in the USA with black young men. The findings from both studies indicated common themes from their stories, particularly with regard to the high levels of disadvantage and social exclusion they had been exposed to in their demographic environments and the anti-social behaviour they described engaging in, prior to the birth of their child/ren. Specifically, a significant proportion of the young men described how they had been immersed in drug and gun crimes and how this shaped their lives and neighbourhoods. Becoming fathers is presented by both sets of young men as rescuing them from this criminal lifestyle.