3,682 research outputs found
On regression adjustments in experiments with several treatments
Regression adjustments are often made to experimental data. Since
randomization does not justify the models, bias is likely; nor are the usual
variance calculations to be trusted. Here, we evaluate regression adjustments
using Neyman's nonparametric model. Previous results are generalized, and more
intuitive proofs are given. A bias term is isolated, and conditions are given
for unbiased estimation in finite samples.Comment: Published in at http://dx.doi.org/10.1214/07-AOAS143 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Limits of Econometrics
In the social and behavioral sciences, far-reaching claims are often made for the superiority of advanced quantitative methods by those who manage to ignore the far-reaching assumptions behind the models. In section 2, we see there was considerable skepticism about disentangling causal processes by statistical modeling. Freedman (2005) examined several well-known modeling exercises, and discovered good reasons for skepticism. Some kinds of problems may yield to sophisticated statistical technique; others will not. The goal of empirical research is or should be to increase our understanding of the phenomena, rather than displaying our mastery of technique.
Some Aspects of the Canadian Experience with Flexible Exchange Rates in the 1970s
In this study, the authors examine three aspects of the Canadian experience with flexible exchange rates in the 1970s: the movements in the Canadian dollar-U.S. dollar exchange rate, the sharp growth of external borrowings by Canadians in the 1974-76 period, and the real effects of relative price movements. Several theoretical and empirical exchange rate models are found to have done poorly in explaining the movements of the value of the Canadian dollar over the decade. In the examination of external borrowings in the mid-1970s, it is concluded that there was some response in borrower and lender behaviour to movements in nominal long-term interest rate differentials. Four sources of explanation for such behaviour are examined. A three-sector model comprising non-tradable goods, resource-based tradable goods and non resource-based tradable goods, is used to study the effects of changes in raw material prices, domestic unit labour costs, and the exchange rate on various real variables in the Canadian economy.
From association to causation: Some remarks on the history of statistics
The ânumerical method â in medicine goes back to Pierre Louis â study of pneumonia (1835), and John Snowâs book on the epidemiology of cholera (1855). Snow took advantage of natural experiments and used convergent lines of evidence to demonstrate that cholera is a waterborne infectious disease. More recently, investigators in the social and life sciences have used statistical models and significance tests to deduce cause-and-effect relationships from patterns of association; an early example is Yuleâs study on the causes of poverty (1899). In my view, this modeling enterprise has not been successful. Investigators tend to neglect the difficulties in establishing causal relations, and the mathematical complexities obscure rather than clarify the assumptions on which the analysis is based. Formal statistical inference is, by its nature, conditional. If maintained hypotheses A, B, C,... hold, then H can be tested against the data. However, if A, B, C,... remain in doubt, so must inferences about H. Careful scrutiny of maintained hypotheses should therefore be a critical part of empirical workâa principle honored more often in the breach than the observance. Snowâs work on cholera will be contrasted with modern studies that depend on statistical models and tests of significance. The examples may help to clarify the limits of current statistical techniques for making causal inferences from patterns of association. 1
Slicing Bing doubles
Bing doubling is an operation which produces a 2-component boundary link B(K)
from a knot K. If K is slice, then B(K) is easily seen to be boundary slice. In
this paper, we investigate whether the converse holds. Our main result is that
if B(K) is boundary slice, then K is algebraically slice. We also show that the
Rasmussen invariant can tell that certain Bing doubles are not smoothly slice.Comment: This is the version published by Algebraic & Geometric Topology on 13
December 200
A transient Markov chain with finitely many cutpoints
We give an example of a transient reversible Markov chain that almost surely
has only a finite number of cutpoints. We explain how this is relevant to a
conjecture of Diaconis and Freedman and a question of Kaimanovich. We also
answer Kaimanovich's question when the Markov chain is a nearest-neighbor
random walk on a tree.Comment: Published in at http://dx.doi.org/10.1214/193940307000000365 the IMS
Collections (http://www.imstat.org/publications/imscollections.htm) by the
Institute of Mathematical Statistics (http://www.imstat.org
Familiarity Breeds Plasticity: Distinct Effects of Experience on Putative Excitatory and Inhibitory Neurons in Inferior Temporal Cortex
Primates have a remarkable capacity to recognize a vast array of visual objects, an ability that depends on experience. In this issue of Neuron, Woloszyn and Sheinberg (2012) report that putative excitatory and inhibitory neurons in inferior temporal cortex exhibit distinct influences long-term visual experience
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