1,971 research outputs found
A common misapplication of statistical inference: nuisance control with null-hypothesis significance tests
Experimental research on behavior and cognition frequently rests on stimulus
or subject selection where not all characteristics can be fully controlled,
even when attempting strict matching. For example, when contrasting patients to
controls, variables such as intelligence or socioeconomic status are often
correlated with patient status. Similarly, when presenting word stimuli,
variables such as word frequency are often correlated with primary variables of
interest. One procedure very commonly employed to control for such nuisance
effects is conducting inferential tests on confounding stimulus or subject
characteristics. For example, if word length is not significantly different for
two stimulus sets, they are considered as matched for word length. Such a test
has high error rates and is conceptually misguided. It reflects a common
misunderstanding of statistical tests: interpreting significance not to refer
to inference about a particular population parameter, but about 1. the sample
in question, 2. the practical relevance of a sample difference (so that a
nonsignificant test is taken to indicate evidence for the absence of relevant
differences). We show inferential testing for assessing nuisance effects to be
inappropriate both pragmatically and philosophically, present a survey showing
its high prevalence, and briefly discuss an alternative in the form of
regression including nuisance variables
A Model for the Self-Organization of Microtubules Driven by Molecular Motors
We propose a two-dimensional model for the organization of stabilized
microtubules driven by molecular motors in an unconfined geometry. In this
model two kinds of dynamics are competing. The first one is purely diffusive,
with an interaction between the rotational degrees of freedom, the second one
is a local drive, dependent on microtubule polarity. As a result, there is a
configuration dependent driving field. Applying a molecular field
approximation, we are able to derive continuum equations. A study on the
solutions shows nonequilibrium steady states. The presence and stability of
such self-organized states are investigated in terms of entropy production.
Numerical simulations confirm analytical results.Comment: 23 pages, 10 figures, LaTeX, ep
Stochastic Resonance in Two Dimensional Landau Ginzburg Equation
We study the mechanism of stochastic resonance in a two dimensional Landau
Ginzburg equation perturbed by a white noise. We shortly review how to
renormalize the equation in order to avoid ultraviolet divergences. Next we
show that the renormalization amplifies the effect of the small periodic
perturbation in the system. We finally argue that stochastic resonance can be
used to highlight the effect of renormalization in spatially extended system
with a bistable equilibria
- …