China
Africa
Explore chapters and articles related to this topic
London’s population and hospitals: 1801–1971
Published in Leslie Mayhew, Urban Hospital Location, 2018
The most convenient way to characterise the population of a city is with the aid of a population density function. Apart from concurring with the theory presented in earlier chapters (particularly Ch. 2), a descriptive model based on a suitable density function is consistent with the intended approach. The critical question is the choice of function and the adequacy with which it portrays essential features of the population of the city. In a wide and growing collection of studies, there is considerable agreement that the distribution of population densities in cities follows a negative exponential distribution. Clark (1951), Muth (1961), Mills (1970) and Bussiere (1972) are representative of early work in this area and in recent years this list has considerably expanded. Most of the possible alternatives to the negative exponential are in fact close mathematical relatives, but the empirical evidence for selecting one rather than another tends in fact to be fairly weak. Zielinski (1980) gives an abridged chronology of examples as indications of the range of variation that has been considered.
S
Published in Filomena Pereira-Maxwell, Medical Statistics, 2018
A depiction of a non-linear relationship between two continuous variables, characterized by an initial slow or no growth phase, followed by growth acceleration in the form of a steeper segment, and a final deceleration or stagnant phase as an asymptotic upper value is approached. This is shown in Figure S.3 (MITCHELL & JAKUBOWSKI, 1999), which models the increasing complication rate with age, in a group of 1172 patients who underwent surgical treatment of unruptured intracranial aneurysms. As the negative exponential curve, this curve is characteristic of constrained population growth, although it differs in that it has an initial phase of slow growth. Sigmoid or S-shaped curves are fitted through non-linear regression. The specific curve obtained depends on the magnitude and direction of the parameters of a given model, and the values of the x-variable. Reverse sigmoid curves - in which there is a slow decline, followed by rapid decline, followed by a return to a slow decline - may also be obtained. HAMILTON (1992; 2012) describes logistic and Gompertz curves as examples of symmetrical and asymmetrical sigmoid curves. Sigmoid curves are also characteristic of cumulative distribution functions (for the Normal, t and logistic probability distributions), and may be fitted to model cumulative response. See also exponential curve, U-shaped curve, J-shaped curve, spline regression.
Describing Within-Person Change Over Time
Published in Lesa Hoffman, Longitudinal Analysis, 2015
The name of the exponential model is derived from the sign of its rate parameter, and not the direction of its change. That is, a negative exponential model could describe a positive rate of change that is slowing down as it approaches an upper asymptote or a negative rate of change that is slowing down as it approaches a lower asymptote (as we will see in our RT data). In contrast, a positive exponential model would include a positive rate parameter to describe a function that is moving away from the asymptote instead (i.e., the function is speeding up). Positive exponential functions are more commonly see in biological applications (e.g., exponential growth of bacteria over time), although they may have other applications as well.
A new alternative quantile regression model for the bounded response with educational measurements applications of OECD countries
Published in Journal of Applied Statistics, 2023
Mustafa Ç. Korkmaz, Christophe Chesneau, Zehra Sedef Korkmaz
Recently, the work on the unit distribution has increased with great interest in many different fields. This is mainly motivated by the practitioner's dissatisfaction with the classic unit distributions. For instance, the beta distribution can be inadequate in order to both model and predict based on the real data phenomena. The beta distribution does not take into account the events of the end zone or more flexibility in specifying the variance. For this aspect, we may refer to [6]. In light of this, the existing unit distributions have generally been elaborated by transforming well-known probability distributions. The main interest of using the transformation based on these distributions is that they do not add new parameters to them on the unit interval. To transform a positive random variable (rv) into new unit rvs, the most used transformation is centered on the negative exponential function. For instance, the Kumaraswamy [31], log-Lindley [17], unit-Weibull [37], unit Gompertz [35], log-xgamma [4], unit inverse Gaussian [16], unit generalized half normal [27], log-weighted exponential [2] and log-extended exponential geometric [22] distributions have been obtained via this method. One may see [3,18,20,26,34] for other unit models that were obtained with other transformation methods. These proposed unit distributions can present more flexible density shapes on the
Implementation of the analytic hierarchy process (AHP) and Fine–Kinney method (FKM) against risk factors to determine the total cost of occupational health and safety precautions in environmental research laboratories
Published in International Journal of Occupational Safety and Ergonomics, 2022
In the last stage, it was investigated whether there is a relationship between safety precautions and accident severities. A negative exponential relationship (y = 86.111e–2.924x) was detected between the safety index (x) and the accident index (y) in the studied laboratories (Figure 2). The determination coefficient (R2) between the safety and accident indexes was calculated as 0.9414 (Figure 2). As can be seen from the negative exponential relationship, the increased safety indexes decreased the accident indexes (Figure 2). Moreover, the ANOVA (one-way) statistical analysis result showed that the relationship between decreased accident indexes and increased safety indexes was found to be significant in this study (α = 0.05, p = 0.002, F = 12.263). It can be concluded that the increased number of safety precautions could decrease the number of working accidents in all studied laboratories. Thus, it was numerically demonstrated that occupational health and safety measures were beneficial to reduce occupational accidents in the content of this study.
Feasibility and Psychometric Integrity of Mobile Phone-Based Intensive Measurement of Cognition in Older Adults
Published in Experimental Aging Research, 2021
Paul W. H. Brewster, Jonathan Rush, Lana Ozen, Rebecca Vendittelli, Scott M. Hofer
To our knowledge, this is the first published study to track cognition longitudinally in a sample of older adults using distributed intensive measurement bursts. Performance variation for both tasks operated primarily at the between-person level, with only 13% of variation in Dot Memory scores and 14% of variation in Symbol Search scores operating longitudinally across bursts. Across-burst slope terms revealed that performance on both tasks tended to improve across the 12 months of observation. Note that this is a small cohort of healthy older adults, and so it is not surprising that practice effects would overshadow any age-or disease-associated declines. Future research in larger samples will permit multigroup analyses to investigate individual differences in these parameters. There is also the potential to apply double negative exponential models to permit delineation of practice gains from other influences on longitudinal change (e.g., Munoz, Sliwinski, Scott, & Hofer, 2016). These analyses are beyond the scope of this sample but will be important outcomes for future research.