5,087 research outputs found
Predicting birth-rates through German micro-census data: a comparison of probit and Boolean regression
This paper investigates the complex interrelationships of qualitative socio-economic variables in the context of Boolean Regression. The data forming the basis for this investigation are from the German Micro-census waves of 1996 2002 and comprise about 400 000 observations. Boolean Regression is used to predict how birth events depend on the socio-economic characteristics of women and their male partners. Boolean Regression is compared to Probit. The data set is split into two halves in order to determine which method yields more accurate predictions. It turns out that Probit is superior, if a given socio-economic type is substantiated by less than about 30 observations, whereas Boolean Regression is superior to Probit, if a given socio-economic type is verified by more than about 30 observations. Therefore a "hybrid" estimation method, combining Probit and Boolean Regression, is proposed and used in the remainder of the paper. Different methods of interpreting the results of the estimations are introduced, relying mainly on simulation techniques. With respect to the reasons for the prevailing low German fertility rates, it is evident that these could be decisively higher if people had higher incomes and earned more with relative ease. From a methodological perspective, the paper demonstrates that Scientific Use Files of socio-economic data comprising hundred thousands or even millions of observations, and which have been made available recently, are the natural field of application for Boolean Regression. Possible consequences for future social and economic research are discussed. --
The effect of climate change on the population of sycamore lace bug (Corythuca ciliata, Say) based on a simulation model with phenological response
Climate change affects on insect populations in many ways: it can cause a shift in geographical spread, abundance, or diversity, it can change the location, the timing and the magnitude of outbreaks of pests and it can define the phenological or even the genetic properties of the species. Long-time investigations of special insect populations, simulation models and scenario studies give us very
important information about the response of the insects far away and near to our century. Getting to know
the potential responses of insect populations to climate change makes us possible to evaluate the
adaptation of pest management alternatives as well as to formulate our future management policy. In this
paper we apply two simple models, in order to introduce a complex case study for a Sycamore lace bug
population. We test how the model works in case the whether conditions are very different from those in
our days. Thus, besides we can understand the processes that happen in present, we can analyze the
effects of a possible climate change, as well
Universal Power-law Decay in Hamiltonian Systems?
The understanding of the asymptotic decay of correlations and of the
distribution of Poincar\'e recurrence times has been a major challenge
in the field of Hamiltonian chaos for more than two decades. In a recent
Letter, Chirikov and Shepelyansky claimed the universal decay for Hamiltonian systems. Their reasoning is based on renormalization
arguments and numerical findings for the sticking of chaotic trajectories near
a critical golden torus in the standard map. We performed extensive numerics
and find clear deviations from the predicted asymptotic exponent of the decay
of . We thereby demonstrate that even in the supposedly simple case, when
a critical golden torus is present, the fundamental question of asymptotic
statistics in Hamiltonian systems remains unsolved.Comment: Phys. Rev. Lett., in pres
Population dynamics of the Sycamore Lace Bug (Corythucha Ciliata, Say, Heteroptera: Tingidae) in Hungary
Based on the observation of more than 10 000 leaves of plane trees, four populations of
Corythucha ciliata (Say, 1832) (Heteroptera: Tingidae) are investigated. After having introduced some
parameters derived from the data, we draw spatial-temporal patterns and describe the seasonal population
dynamics of Corythucha ciliata. Amongst others, the temporal change of the density of population, the
state plane of larvae–adults, the inclination to accumulate, and the intraspecific competition are examined.
Population and biomass dynamics is characterized for populations with and without limited nutrient
source in case of different weather circumstances and effects
Zoocoenological state of microhabitats and its seasonal dynamics in an aquatic macroinvertebrate assembly (Hydrobiological case studies on lake Balaton, No. 1.)
In the years 2002, 2003 and 2004 we collected samples of macroinvertebrates on a total of 36
occasions in Badacsony bay, in areas of open water (in the years 2003 and 2004 reed-grassy) as well as
populated by reed (Phragmites australis) and cattail (Typha angustifolia). Samples were taken using a stiff
hand net. The sampling site includes three microhabitats differentiated only by the aquatic plants inhabiting
these areas. Our data was gathered from processing 208 individual samples. The quantity of
macroinvertebrates is represented by biovolume value based on volume estimates. We can identify taxa in
abundant numbers found in all water types and ooze; as well as groups associated with individual microhabitats
with various aquatic plants. We can observe a notable difference between the years in the volume of
invertebrate macrofauna caused by the drop of water level, and the multiplication of submerged macrophytes.
There are smaller differences between the samples taken in reeds and cattail stands. In the second
half of 2003 – which was a year of drought – the Najas marina appeared in open waters and allowed to
support larger quantities of macroinvertebrates. In 2004 with higher water levels, the Potamogeton perfoliatus
occurring in the same area has had an even more significant effect. This type of reed-grass may support
the most macroinvertebrates during the summer. From the aspect of diversity relations we may suspect
different characteristics. The reeds sampling site proved to be the richest, while the cattail microhabitat is
close behind, open water (with submerged macrophytes) is the least diverse microhabitat
Ecosystems as climate controllers – biotic feedbacks (a review)
There is good evidence that higher global temperature will promote a rise of green house gas levels, implying a positive feedback which will increase the effect of the anthropogenic emissions on global temperatures. Here we present a review about the results which deal with the possible feedbacks
between ecosystems and the climate system. There are a lot of types of feedback which are classified.
Some circulation models are compared to each other regarding their role in interactive carbon cycle
Seasonal dynamics of an aquatic macroinvertebrate assembly (Hydrobiological case study of Lake Balaton No. 2)
In 2002, 2003 and 2004, we took macoinvertebrate samples on a total of 36 occasions at the
Badacsony bay of Lake Balaton. Our sampling site was characterised by areas of open water (in 2003 and
2004 full of reed-grass) as well as by areas covered by common reed (Phragmites australis) and narrowleaf
cattail (Typha angustifolia). Samples were taken both from water body and benthic ooze by use of a
stiff hand net. We have gained our data from processing 208 individual samples. We took samples
frequently from early spring until late autumn for a deeper understanding of the processes of seasonal
dynamics. The main seasonal patterns and temporal changes of diversity were described. We constructed
a weather-dependent simulation model of the processes of seasonal dynamics in the interest of a possible
further utilization of our data in climate change research. We described the total number of individuals,
biovolume and diversity of all macroinvertebrate species with a single index and used the temporal trends
of this index for simulation modelling. Our discrete deterministic model includes only the impact of
temperature, other interactions might only appear concealed. Running the model for different climate
change scenarios it became possible to estimate conditions for the 2070-2100 period. The results,
however, should be treated very prudently not only because our model is very simple but also because the
scenarios are the results of different models
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