Causal simulation experiments: Lessons from bias amplification

Recent theoretical work in causal inference has explored an important class of variables which, when conditioned on, may further amplify existing unmeasured confounding bias (bias amplification). Despite this theoretical work, existing simulations of bias amplification in clinical settings have suggested bias amplification may not be as important in many practical cases as suggested in the theoretical literature. We resolve this tension by using tools from the semi-parametric regression literature leading to a general characterization in terms of the geometry of OLS estimators which allows us to extend current results to a larger class of DAGs, functional forms, and distributional assumptions. We further use these results to understand the limitations of current simulation approaches and to propose a new framework for performing causal simulation experiments to compare estimators. We then evaluate the challenges and benefits of extending this simulation approach to the context of a real clinical data set with a binary treatment, laying the groundwork for a principled approach to sensitivity analysis for bias amplification in the presence of unmeasured confounding.

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Trade and Early State Formation in the Northern Titicaca Basin, Peru

Latin American Antiquity ◽

10.7183/1045-6635.24.3.289 ◽

2013 ◽

Vol 24 (3) ◽

pp. 289-308 ◽

Cited By ~ 4

Author(s):

Abigail Levine ◽

Charles Stanish ◽

P. Ryan Williams ◽

Cecilia Chávez ◽

Mark Golitko

Keyword(s):

Social Evolution ◽

Theoretical Work ◽

Long Distance ◽

Data Set ◽

Exchange Networks ◽

Multiple Strategies ◽

Regional Center ◽

Recent Theoretical Work ◽

Titicaca Basin ◽

Archaic States

Recent theoretical work has underscored the importance of multiple strategies in the dynamic political and economic landscapes in which archaic states developed. This research emphasizes how the interaction among various non-state polities drives the growth of political centers within a region. It is in this context that numerous intermediate peer-polities emerged, and, on rare occasions in a few places around the world, it is the context of state development. War and trade have emerged as particularly important forms of strategic interaction in the theoretical literature, representing strategies of both cooperation and competition between and within complex, non-state polities. In this paper we present a detailed case study that tests and illustrates one of these theoretical propositions. We examine the role of trade in this process of social evolution as evidenced in the northern Titicaca Basin ca. 500 B.C.—A.D. 300. Based on intensive analyses of a large excavated data set, we suggest that the emergence of one regional center, called Taraco, is strongly linked to strategic participation in local and long-distance exchange networks.

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Micro Effects of Macro Announcements: Real-Time Price Discovery in Foreign Exchange

The American Economic Review ◽

10.1257/000282803321455151 ◽

2003 ◽

Vol 93 (1) ◽

pp. 38-62 ◽

Cited By ~ 725

Author(s):

Torben G Anderson ◽

Tim Bollerslev ◽

Francis X Diebold ◽

Clara Vega

Keyword(s):

Exchange Rate ◽

Real Time ◽

Price Discovery ◽

Theoretical Work ◽

Good News ◽

Data Set ◽

Exchange Rate Dynamics ◽

Recent Theoretical Work ◽

Time Price ◽

Conditional Means

Using a new data set consisting of six years of real-time exchange-rate quotations, macroeconomic expectations, and macroeconomic realizations, we characterize the conditional means of U.S. dollar spot exchange rates. In particular, we find that announcement surprises produce conditional mean jumps; hence high-frequency exchange-rate dynamics are linked to fundamentals. The details of the linkage are intriguing and include announcement timing and sign effects. The sign effect refers to the fact that the market reacts to news in an asymmetric fashion: bad news has greater impact than good news, which we relate to recent theoretical work on information processing and price discovery.

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Some Empirical Tests of Duration-of-Stay Effects in Intraurban Migration

Environment and Planning A Economy and Space ◽

10.1068/a091357 ◽

1977 ◽

Vol 9 (12) ◽

pp. 1357-1374 ◽

Cited By ~ 49

Author(s):

W A V Clark ◽

J O Huff

Keyword(s):

Theoretical Work ◽

Metropolitan Region ◽

Data Set ◽

Duration Of Stay ◽

History Effects ◽

Recent Theoretical Work ◽

Individual Household ◽

Empirical Tests ◽

Weak Influence

Although there have been several empirical tests of the cumulative inertia hypothesis, the more recent theoretical work by Ginsberg (1973), McFarland (1970), and Spilerman (1972b) suggests that whereas these tests may support the existence of duration-of-stay effects they do not prove the existence of cumulative inertia as defined by McGinnis (1968). The tests are replicated and a new group of tests are applied to a data set of individual household moves for the Milwaukee metropolitan region. The new tests attempt to distinguish between the effects of heterogeneity, cumulative inertia, and changes in the rates of mobility. The results emphasize that even when cumulative inertia exists it is a very weak influence on the probability of migrating and that duration of stay since the last move is an inadequate measure of residence history effects.

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The light-scattering Mueller matrices for Rayleigh and Rayleigh-Gans-Debye approximation

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19902889 ◽

1990 ◽

Vol 55 (12) ◽

pp. 2889-2897

Author(s):

Jaroslav Holoubek

Keyword(s):

Light Scattering ◽

Theoretical Work ◽

Matrix Elements ◽

Elastic Light Scattering ◽

Yield Information ◽

Recent Theoretical Work ◽

Particle Parameters ◽

Complete Set ◽

Single Matrix ◽

Scattering Matrix Elements

Recent theoretical work has shown that the complete set of polarized elastic light-scattering studies should yield information about scatterer structure that has so far hardly been utilized. We present here calculations of angular dependences of light-scattering matrix elements for spheres near the Rayleigh and Rayleigh-Gans-Debye limits. The significance of single matrix elements is documented on examples that show how different matrix elements respond to changes in particle parameters. It appears that in the small-particle limit (Rg/λ < 0.1) we do not loose much information by ignoring "large particle" observables.

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The Negative Intelligence–Religiosity Relation: New and Confirming Evidence

Personality and Social Psychology Bulletin ◽

10.1177/0146167219879122 ◽

2019 ◽

Vol 46 (6) ◽

pp. 856-868 ◽

Cited By ~ 5

Author(s):

Miron Zuckerman ◽

Chen Li ◽

Shengxin Lin ◽

Judith A. Hall

Keyword(s):

Cognitive Ability ◽

Cognitive Style ◽

Religious Beliefs ◽

Meta Analysis ◽

Theoretical Work ◽

Data Set ◽

Analytic Cognitive Style

Zuckerman et al. (2013) conducted a meta-analysis of 63 studies that showed a negative intelligence–religiosity relation (IRR). As more studies have become available and because some of Zuckerman et al.’s (2013) conclusions have been challenged, we conducted a new meta-analysis with an updated data set of 83 studies. Confirming previous conclusions, the new analysis showed that the correlation between intelligence and religious beliefs in college and noncollege samples ranged from −.20 to −.23. There was no support for mediation of the IRR by education but there was support for partial mediation by analytic cognitive style. Thus, one possible interpretation for the IRR is that intelligent people are more likely to use analytic style (i.e., approach problems more rationally). An alternative (and less interesting) reason for the mediation is that tests of both intelligence and analytic style assess cognitive ability. Additional empirical and theoretical work is needed to resolve this issue.

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Magnetospheric Structure of Rotation-Powered Neutron Stars

International Astronomical Union Colloquium ◽

10.1017/s0002731600154770 ◽

1992 ◽

Vol 128 ◽

pp. 56-77 ◽

Cited By ~ 7

Author(s):

Jonathan Arons

Keyword(s):

Radio Emission ◽

Gamma Radiation ◽

Heavy Ions ◽

Theoretical Work ◽

Future Research ◽

Observational Constraints ◽

Polar Caps ◽

Recent Theoretical Work ◽

Density Flow ◽

Promising Avenue

AbstractI survey recent theoretical work on the structure of the magnetospheres of rotation-powered pulsars, within the observational constraints set by their observed spindown, their ability to power synchrotron nebulae and their ability to produce beamed collective radio emission, while putting only a small fraction of their energy into incoherent X- and gamma radiation. I find no single theory has yet given a consistent description of the magnetosphere, but I conclude that models based on a dense outflow of pairs from the polar caps, permeated by a lower density flow of heavy ions, are the most promising avenue for future research.

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THE EXOTIC BARIUM BISMUTHATES

International Journal of Modern Physics B ◽

10.1142/s0217979296000362 ◽

1996 ◽

Vol 10 (08) ◽

pp. 863-955 ◽

Cited By ~ 27

Author(s):

A. TARAPHDER ◽

RAHUL PANDIT ◽

H. R. KRISHNAMURTHY ◽

T. V. RAMAKRISHNAN

Keyword(s):

Bound States ◽

Random Phase ◽

Density Wave ◽

Mean Field ◽

Experimental Tests ◽

Theoretical Work ◽

Recent Theoretical Work ◽

Effects Of Disorder ◽

Exotic Physics ◽

Transport Gaps

We review the remarkable properties, including superconductivity, charge-density-wave ordering and metal–insulator transitions, of lead- and potassium-doped barium bismuthate. We will discuss some of the early theoretical studies of these systems. Our recent theoretical work, on the negative-U, extended-Hubbard model for these systems, will also be described. Both the large- and intermediate-U regimes of this model were examined, using mean-field and random-phase approximations, particularly with a view to fitting various experimental properties of these bismuthates. On the basis of our studies, we point out possibilities for exotic physics in these systems. We also emphasize the different consequences of electronic and phonon-mediated mechanisms for the negative U. We show that, for an electronic mechanism, the semiconducting phases of these bismuthates must be unique, with their transport properties dominated by charge±2eCooperon bound states. This can explain the observed difference between the optical and transport gaps. We propose other experimental tests for this novel mechanism of charge transport and comment on the effects of disorder.

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Determination of Reactivity Ratios from Binary Copolymerization Using the k-Nearest Neighbor Non-Parametric Regression

Polymers ◽

10.3390/polym13213811 ◽

2021 ◽

Vol 13 (21) ◽

pp. 3811

Author(s):

Iosif Sorin Fazakas-Anca ◽

Arina Modrea ◽

Sorin Vlase

Keyword(s):

Experimental Data ◽

Nearest Neighbor ◽

Optimization Method ◽

Reactivity Ratios ◽

Data Sets ◽

K Nearest Neighbor ◽

Integration Algorithm ◽

Data Set ◽

Parametric Regression ◽

Non Parametric

This paper proposes a new method for calculating the monomer reactivity ratios for binary copolymerization based on the terminal model. The original optimization method involves a numerical integration algorithm and an optimization algorithm based on k-nearest neighbour non-parametric regression. The calculation method has been tested on simulated and experimental data sets, at low (<10%), medium (10–35%) and high conversions (>40%), yielding reactivity ratios in a good agreement with the usual methods such as intersection, Fineman–Ross, reverse Fineman–Ross, Kelen–Tüdös, extended Kelen–Tüdös and the error in variable method. The experimental data sets used in this comparative analysis are copolymerization of 2-(N-phthalimido) ethyl acrylate with 1-vinyl-2-pyrolidone for low conversion, copolymerization of isoprene with glycidyl methacrylate for medium conversion and copolymerization of N-isopropylacrylamide with N,N-dimethylacrylamide for high conversion. Also, the possibility to estimate experimental errors from a single experimental data set formed by n experimental data is shown.

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Landauer in the age of synthetic biology: energy consumption and information processing in biochemical networks

10.1101/020594 ◽

2015 ◽

Cited By ~ 1

Author(s):

Pankaj Mehta ◽

Alex H Lang ◽

David J Schwab

Keyword(s):

Information Processing ◽

Energy Consumption ◽

Synthetic Biology ◽

Protein Modification ◽

Theoretical Work ◽

Biochemical Networks ◽

Fundamental Physics ◽

Recent Theoretical Work ◽

Cellular Circuits ◽

Molecular Components

A central goal of synthetic biology is to design sophisticated synthetic cellular circuits that can perform complex computations and information processing tasks in response to specific inputs. The tremendous advances in our ability to understand and manipulate cellular information processing networks raises several fundamental physics questions: How do the molecular components of cellu- lar circuits exploit energy consumption to improve information processing? Can one utilize ideas from thermodynamics to improve the design of synthetic cellular circuits and modules? Here, we summarize recent theoretical work addressing these questions. Energy consumption in cellular cir- cuits serves five basic purposes: (1) increasing specificity, (2) manipulating dynamics, (3) reducing variability, (4) amplifying signal, and (5) erasing memory. We demonstrate these ideas using several simple examples and discuss the implications of these theoretical ideas for the emerging field of synthetic biology. We conclude by discussing how it may be possible to overcome these limitations using “post-translational” synthetic biology that exploits reversible protein modification.

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Mixed-polarity random-dot stereograms alter GABA and Glx concentration in the early visual cortex

10.1101/549980 ◽

2019 ◽

Author(s):

Reuben Rideaux ◽

Nuno Goncalves ◽

Andrew E Welchman

Keyword(s):

Visual Cortex ◽

Three Dimensional ◽

Theoretical Work ◽

Dimensional Structure ◽

Resonance Spectroscopy ◽

Gaba Concentration ◽

Recent Theoretical Work ◽

Random Dot Stereograms ◽

Mixed Polarity ◽

Early Visual Cortex

ABSTRACTThe offset between images projected onto the left and right retinae (binocular disparity) provides a powerful cue to the three-dimensional structure of the environment. It was previously shown that depth judgements are better when images comprise both light and dark features, rather than only dark or only light elements. Since Harris and Parker (1995) discovered the “mixed-polarity benefit”, there has been limited evidence supporting their hypothesis that the benefit is due to separate bright and dark channels. Goncalves and Welchman (2017) observed that single- and mixed-polarity stereograms evoke different levels of positive and negative activity in a deep neural network trained on natural images to make depth judgements, which also showed the mixed-polarity benefit. Motivated by this discovery, here we seek to test the potential for changes in the balance of excitation and inhibition that are produced by viewing these stimuli. In particular, we use magnetic resonance spectroscopy to measure Glx and GABA concentration in the early visual cortex of adult humans while viewing single- and mixed-polarity random-dot stereograms (RDS). We find that observers’ Glx concentration is significantly higher while GABA concentration is significantly lower when viewing mixed-polarity RDS than when viewing single-polarity RDS. These results indicate that excitation and inhibition facilitate processing of single- and mixed-polarity stereograms in the early visual cortex to different extents, consistent with recent theoretical work (Goncalves & Welchman, 2017).

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