Borrowing from Yourself: The Determinants of 401(k) Loan Patterns

This paper explores the determinants of people’s decisions to take 401(k) loans. We argue that 401(k) plans do not simply represent retirement saving, but they also provide a means of saving for precautionary purposes. We model factors that rationally would induce people to borrow from their pension plans, and we explain why people do not often use 401(k) loans to replace their more expensive credit card debt. Next we test our hypotheses using a rich dataset and show that people who are liquidity-constrained are more likely to have plan loans, while the better-off take larger loans when they do borrow. Plan characteristics such as the number of loans allowed also influence borrowing and loan size in interesting ways, while loan interest rates have only a small impact.

A pilot study on constructing a Scottish sectoral CO2 emissions account

To calculate polluting emissions, the Scottish economy was divided into 76 sectors and the pollution attributable to each sector was estimated. We used emission/output ratios for the UK, but then further adjusted estimated Scottish emissions, using the ratio of economic activity for each sector between Scotland and the UK

The environmental "trade balance" between Scotland and the rest of the UK : an inter-regional input-output and SAM analysis

We use an inter-regional input-output (IO) and social accounting matrix (SAM) pollution attribution framework to serve as a platform for sub-national environmental attribution and trade balance analysis. While the existence of significant data problems mean that the quantitative results of this study should be regarded as provisional, the inter-regional economy-environment IO and SAM framework for Scotland and the rest of the UK (RUK) allows an illustrative analysis of some very important issues. There are two key findings. The first is that there are large environmental spillovers between the regions of the UK. This has implications in terms of the devolution of responsibility for achieving targets for reductions in emissions levels and the need for policy co-ordination between the UK national and devolved governments. The second finding is that whilst Scotland runs an economic trade deficit with RUK, the environmental trade balance relationship for the main greenhouse gas, CO2, runs in the opposite direction. In other words, the findings of this study suggest the existence of a CO2 trade surplus between Scotland and the rest of the UK. This suggests that Scotland is bearing a net loss in terms of pollutants as a result of inter-union trade. However, if Scotland can carry out key activities, such as electricity generation, using less polluting technology, it is better for the UK as a whole if this type of relationship exists. Thus, the environmental trade balance is an important part of the devolution settlement

Traveling waves of selective sweeps

The goal of cancer genome sequencing projects is to determine the genetic alterations that cause common cancers. Many malignancies arise during the clonal expansion of a benign tumor which motivates the study of recurrent selective sweeps in an exponentially growing population. To better understand this process, Beerenwinkel et al. [PLoS Comput. Biol. 3 (2007) 2239--2246] consider a Wright--Fisher model in which cells from an exponentially growing population accumulate advantageous mutations. Simulations show a traveling wave in which the time of the first $k$-fold mutant, $T_k$, is approximately linear in $k$ and heuristics are used to obtain formulas for $ET_k$. Here, we consider the analogous problem for the Moran model and prove that as the mutation rate $\mu\to0$, $T_k\sim c_k\log(1/\mu)$, where the $c_k$ can be computed explicitly. In addition, we derive a limiting result on a log scale for the size of $X_k(t)={}$the number of cells with $k$ mutations at time $t$.Comment: Published in at http://dx.doi.org/10.1214/10-AAP721 the Annals of Applied Probability (http://www.imstat.org/aap/) by the Institute of Mathematical Statistics (http://www.imstat.org

Blind Signal Detection in Massive MIMO: Exploiting the Channel Sparsity

In practical massive MIMO systems, a substantial portion of system resources are consumed to acquire channel state information (CSI), leading to a drastically lower system capacity compared with the ideal case where perfect CSI is available. In this paper, we show that the overhead for CSI acquisition can be largely compensated by the potential gain due to the sparsity of the massive MIMO channel in a certain transformed domain. To this end, we propose a novel blind detection scheme that simultaneously estimates the channel and data by factorizing the received signal matrix. We show that by exploiting the channel sparsity, our proposed scheme can achieve a DoF very close to the ideal case, provided that the channel is sufficiently sparse. Specifically, the achievable degree of freedom (DoF) has a fractional gap of only $1/T$ from the ideal DoF, where $T$ is the channel coherence time. This is a remarkable advance for understanding the performance limit of the massive MIMO system. We further show that the performance advantage of our proposed scheme in the asymptotic SNR regime carries over to the practical SNR regime. Numerical results demonstrate that our proposed scheme significantly outperforms its counterpart schemes in the practical SNR regime under various system configurations.Comment: 32 pages, 9 figures, submitted to IEEE Trans. Commu

Equilibrium Exchange Rate in the Czech Republic: How Good is the Czech BEER?

This paper investigates the equilibrium exchange rate of the Czech koruna using the reduced form equation of the stock-flow approach advocated, for instance, by Faruqee (1995) and Alberola and others (1999). We investigate whether or not the observed real exchange rate of the Czech koruna is close to its equilibrium value over the period from 1993 to 2004. Our empirical approach is tantamount to the Behavioural Equilibrium Exchange Rate (BEER) popularised by MacDonald (1997) and Clark and MacDonald (1998) in that the Czech real exchange rate vis-à-vis the euro is regressed on the dual productivity differential and the net foreign assets position, based on which actual and total misalignment figures are derived in a time series context. In other words, we check the quality of the Czech BEER. We also study the impact of a possible initial undervaluation on the estimated equilibrium exchange rate. Employing monthly time series from 1993:M1 to 2004:M9 and applying several alternative cointegration techniques, we identify a period of an overvaluation in 1997 and in 1999, an increasing overvaluation till 2002, an undervaluation in 2003 and a correction towards equilibrium in the second half of 2004http://deepblue.lib.umich.edu/bitstream/2027.42/40167/3/wp781.pd