A Unifying Framework and Comparison of Algorithms for Non-negative Matrix Factorisation

Non-negative matrix factorisation (NMF) is an increasingly popular unsupervised learning method. However, parameter estimation in the NMF model is a difficult high-dimensional optimisation problem. We consider algorithms of the alternating least squares type. Solutions to the least squares problem fall in two categories. The first category is iterative algorithms, which include algorithms such as the majorise–minimise (MM) algorithm, coordinate descent, gradient descent and the Févotte-Cemgil expectation–maximisation (FC-EM) algorithm. We introduce a new family of iterative updates based on a generalisation of the FC-EM algorithm. The coordinate descent, gradient descent and FC-EM algorithms are special cases of this new EM family of iterative procedures. Curiously, we show that the MM algorithm is never a member of our general EM algorithm. The second category is based on cone projection. We describe and prove a cone projection algorithm tailored to the non-negative least square problem. We compare the algorithms on a test case and on the problem of identifying mutational signatures in human cancer. We generally find that cone projection is an attractive choice. Furthermore, in the cancer application, we find that a mix-and-match strategy performs better than running each algorithm in isolation.     

Exchange Rates and the Conversion of Currency‐Specific Risk Premia

How do the risk factors that drive asset prices influence exchange rates? Are the parameters of asset price processes relevant for specifying exchange rate processes? Most international asset pricing models focus on the analysis of asset returns given exchange rate processes. Little work has been done on the analysis of exchange rates dependent on asset returns. This paper uses an international stochastic discount factor (SDF) framework to analyse the interplay between asset prices and exchange rates. So far, this approach has only been implemented in international term structure models. We find that exchange rates serve to convert currency‐specific discount factors and currency‐specific prices of risk – a result linked to the international arbitrage pricing theory (IAPT). Our empirical investigation of exchange rates and stock markets of four countries presents evidence for the conversion of currency‐specific risk premia by exchange rates.     

Market Conduct and Endogenous Lobbying: Evidence from the U.S. Mobile Telecommunications Industry

This paper empirically explores the relationship between firms' market behavior and their lobbying activities in a regulated market. In particular, we investigate whether the amount of contributions offered by cellular service providers to fund the campaigns of political parties affected market conduct in the early US mobile telecommunications industry. We structurally estimate market interactions while taking the potential endogeneity of lobbying decisions into account. Our results show that competition was more intense in those states where campaign contributions by the cellular industry have been higher. Furthermore, we reject the hypothesis that lobbying activities can be regarded as exogenous in the study of market conduct.     

Observation of a strategic household purchase decision

The present paper focuses on strategic household purchase decisions; i.e., major, complex buying decisions with long-term bindings of economic resources. An in-depth study of house buying in two-career households demonstrated preferences (goals) to be ambiguous, and consequences to be modestly understood and partly uncovered after the purchase. Only a few alternatives were considered, and they were from different broad need-satisfying categories such as purchase of apartment or house, or renting. No direct comparisons of alternatives were observed to take place. The purchase decisions were based on few, very crude decision criteria working as guidelines for judging whether or not the alternatives considered were acceptable, while the final choice seemingly was made according to an affect-referral decision rule.     

Determinants of discounts in equity rights issues: An international comparison

Equity rights offerings are the predominant SEO flotation method in many European and Asian countries. Several previous studies focus on rights offerings, but these studies often measure solely the announcement effects of these offerings and pay little attention to the discount. This study seeks to close this gap, explain the discounts on such rights offerings, and determine the drivers of offering discounts with a focus on cultural effects regarding the level of uncertainty avoidance. Based on the existing literature, we develop several hypotheses and find supporting evidence for these hypotheses in our data. Our main finding is that the most important factors for explaining the discount on an equity rights offer are the level of uncertainty avoidance, the quality of a firm, and the level of uncertainty about firm value.     

Online display advertising for CPG brands: (When) does it work?

This study examines how online display ads, alone or in combination with more conventional media (television and print), can help drive sales in the consumer packaged goods (CPG) sector. It also assesses how the combined sales effect of online and offline ads depends on the volatility of their expenditures over time. We explore these relations for 154 brands across 68 Dutch CPG product categories. We find that, even though display ads are not effective for the “average” CPG brand, they do have a significant impact for a sizable, and considerably larger than expected by chance, subset of brands. Importantly, this impact depends on the type of product. While display ads are found to be ineffective for low-involvement utilitarian products, they can significantly enhance sales for other CPG product types. Moreover, the effect depends on whether they are used in combination with other media: while display ads are best used as a stand-alone medium for high-involvement utilitarian products, it is better to combine them with traditional media for hedonic products. Finally, the long-term effectiveness of display messages increases significantly when they are spread more evenly in time.     

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