Approximate maximum likelihood estimation for stochastic differential equations with random effects in the drift and the diffusion

Consider N independent stochastic processes \((X_i(t), t\in [0,T])\), \(i=1,\ldots , N\), defined by a stochastic differential equation with random effects where the drift term depends linearly on a random vector \(\Phi _i\) and the diffusion coefficient depends on another linear random effect \(\Psi _i\). For these effects, we consider a joint parametric distribution. We propose and study two approximate likelihoods for estimating the parameters of this joint distribution based on discrete observations of the processes on a fixed time interval. Consistent and \(\sqrt{N}\)-asymptotically Gaussian estimators are obtained when both the number of individuals and the number of observations per individual tend to infinity. The estimation methods are investigated on simulated data and show good performances.     

Increasing the credibility of the twin birth instrument

Twin births are an important instrument for the endogenous fertility decision. However, twin births are not exogenous either as dizygotic twinning is correlated with maternal characteristics. Following the medical literature, we assume that monozygotic twins are exogenous, and construct a new instrument, which corrects for the selection although monozygotic twinning is usually unobserved in survey and administrative datasets. Using administrative data from Sweden, we show that the usual twin instrument is related to observed and unobserved determinants of economic outcomes, while our new instrument is not. In our applications we find that the classical twin instrument underestimates the negative effect of fertility on labor income. This finding is in line with the observation that high earners are more likely to delay childbearing and hence have a higher risk to get dizygotic twins.     

Recombination in digital innovation: Challenges,opportunities, and the importance of a theoretical framework

In this article I argue that the quest to establish digital innovation as a research domain is hindered by three challenges. As digital innovation research we are too often: a) reifying the agency of digital innovation actors; b) developing explanations of digital innovation detached from the specifics of digital technology, and c) developing overly specific explanations of digital innovation. I begin by providing a brief overview of the recombination perspective and considering why this perspective holds great appeal in the digital age. I then engage with Henfridsson et al.'s (2018) value spaces framework as a platform for framing value creation and value capture in relation to recombination in digital innovation. Next, I push Henfridsson et al.'s arguments one step further to discuss them in relation to what I consider to be the key challenges for digital innovation research. Illustrating with some of my own recent projects, I suggest that in order to fully address these challenges we need to (1) develop explanations of digital innovation acknowledging the complexity of sociomaterial interaction in digital innovation; (2) develop explanations of digital innovation building on the specifics of digital technology, and (3) develop explanations of digital innovation based on an oscillation between the specific and the general. The article concludes by pointing to future challenges and developments for digital innovation research.     

Accounting for Negative,Zero and Positive Willingness to Pay for Landscape Change in a National Park

In contingent valuation, despite the fact that many externalities manifest themselves as costs to some and benefits to others, most studies restrict willingness to pay to being non‐negative. In this paper, we investigate the impact of allowing for negative, zero and positive preferences for prospective changes in woodland cover in two UK national parks, the Lake District and the Trossachs. An extended spike model is used to accomplish this. The policy implications of not allowing for negative values in terms of aggregate benefits are also investigated, by comparing the extended spike model with a simple spike making use of only zero and positive bids, and a model which considers positive bids only. We find that ignoring negative values over‐states the aggregate benefits of a woodland planting project by up to 44%.     

Digitale Spaltung im Zeitalter der S?ttigung

Using Bourdieu??s Habitus-Capital theory and a representative dataset this study shows that social position influences internet use. The study is thus connected to the research about thedigital divide. A secondary analysis of the ACTA 2008 (n?=?7.623, representative of Germans between 14 and 64 years who use the internet) shows on the one hand that there are still gaps in internet usage (gender, generation, and education gap). On the other hand the results indicate acapital gap. Since the accumulation of capital in the internet is connected with education as well as economic status, there is a threat of a downward spiral: Those who have less capital (education, money) gather less internet knowledge. Since cultural capital influences a person??s social position, internet use enhances social inequality.     

Social networks and small business performance in West African border regions

This paper studies the links between economic performance and social networks in West Africa. Using data collected on 358 small-scale traders in five border markets, we show that social networks can be simultaneously a resource which positively contributes to labour market outcomes and a social burden that has a negative economic impact. Testing the effect of social networks between small traders and three categories of actors, we find that the most well-connected actors are also the most successful in terms of monthly profit. The effects of social networks are, however, dependent on the type of persons with whom traders are connected. We show that support received from state representatives and politicians is converted into economic performance, while the impact of law enforcement officers on the monthly profits of traders is not significant. We also find that interacting with traditional religious leaders has a negative effect on economic performance. Our work has two implications: Firstly, collecting data on social networks remains challenging due to endogeneity. Secondly, network-enhancing policies should aim at improving both the internal connectivity of economic actors at the local level and their external connectivity with the rest of the world.     

The impact of advertising content on movie revenues

We analyze the contents of print ads in the motion picture industry (e.g., number of reviews quoted in the ad, the presence of a top reviewer, size of the ad, star, director, etc.). We find that external validation (a recommendation by a top reviewer) is more important to revenues than the informative content of the ad.     

Unobserved firm heterogeneity and the size-exports nexus: Evidence from German panel data

This paper starts from the stylized fact that firm size and exporting tends to be positively related. Using large sets of establishment panel data for three different industries from official statistics, evidence is presented that the familiar picture of an export/sales ratio that increases (at a decreasing rate) with firm size vanishes if unobserved firm heterogeneity is controlled for in a fixed-effects fractional logit regression model. This finding is well in line with the fact that many small firms are “hidden export champions.” JEL no. F10, D21, L60     

Coordination in retailer-carrier channels for long term planning

We study a retailer-carrier channel for the purpose of long term planning and coordination. Here, the term channel represents the business interaction between the retailer and the carrier. The retailer sells a particular item with price-dependent demand, whereas the carrier is responsible for transporting the item to the retailer's site. We characterize the profit functions of each channel member as well as the total channel profit. We consider two specific channel structures: (i) the centralized channel and (ii) the decentralized channel. Under the first channel structure, the goal is to set the retail price so as to maximize the total channel profit. Under the latter, the carrier and the retailer choose their own policy parameters, i.e., the freight rate for the carrier and the retail price for the retailer, so as to maximize their individual profits. We model the decentralized channel as a Stackelberg Game and propose a coordination mechanism between the retailer and the carrier in which the retailer signals a price multiplier to the carrier. We illustrate that this mechanism could provide win-win solutions for both parties and present analytical and numerical results on the efficiency of channel coordination. We demonstrate that coordination in retailer-carrier channels can be as promising as supplier-retailer channels. We also discuss the effects of retailer-carrier coordination on inventory levels.