Sequential sampling in the search for new shared species

In microbial sciences, as well as other disciplines, it is often valuable to sample communities in a sequential or group sequential manner, in order to determine their structure or their similarity. We develop sequential sampling procedures to accomplish this by first assuming that one observation is drawn with replacement from each population at a time. Suppose that the sampling is terminated after n pairs of observations and k shared species were discovered, and assume that we receive payoff h(k)−cn, where h(k) is non-decreasing and the sampling cost c is non-negative. Similar to Rasmussen and Starr (1979), we show that an optimal stopping rule exists if h(k+1)−h(k) is non-increasing. An analogous result holds for group sequential sampling. This leads to using an estimate of the probability of discovering new shared species as a stopping indicator for comparing two populations with respect to the similarity index. We show by simulation and real examples that this is a feasible approach which can help to reduce the sample size.     

Dynamic Pricing and Demand Estimation for a Single Unique Asset*

We address the situation of a firm that needs to dispose of a large, expensive asset (e.g., car, machine tool, earth mover, turbine, house, airplane), with or without a given deadline (and either known or unknown to the buyer). If a deadline exists, the asset is salvaged at a known value which may be zero, or even negative if there is a disposal cost. The asset has a known holding cost and may also have an initial nominal (undiscounted) price. The question is how, if at all, the price should be discounted as time progresses to maximize the expected proceeds. We use a dynamic recursion where each decision stage can be optimized based on classic economic monopoly pricing theory with a demand intensity function estimated from sales data, and show that the model is well‐behaved in the sense that the optimal price and optimal expected revenue monotonically decline as the deadline approaches. We test the model by comparing its optimal price pattern to the official pricing policy practiced at a used‐car dealer. We then extend the model to situations where the buyer knows the seller's deadline and thus may alter his behavior as the deadline approaches.     

Compositional and Temporal Dynamics of International Migration in the EU/EFTA: A New Metric for Assessing Countries’ Immigration and Integration Policies

In this article, I derive estimates of migrants’ expected years of residence in each of 31 countries in the European Union and European Free Trade Association each year from 2002 to 2007. A country‐level measure summarizing the temporal dynamics of international migration, I compare my results against the often used compositional measure of the percent foreign born, and show that these two measures reflect different population processes. I likewise demonstrate the utility of the measure derived here as a tool to assess countries’ integration policies on long‐term residence per their scores in the Migrant Integration Policy Index. Key theoretical and policy implications are discussed.     

The Multiple Control of Verbal Behavior

Amid the novel terms and original analyses in Skinner's Verbal Behavior, the importance of his discussion of multiple control is easily missed, but multiple control of verbal responses is the rule rather than the exception. In this paper we summarize and illustrate Skinner's analysis of multiple control and introduce the terms convergent multiple control and divergent multiple control. We point out some implications for applied work and discuss examples of the role of multiple control in humor, poetry, problem solving, and recall. Joint control and conditional discrimination are discussed as special cases of multiple control. We suggest that multiple control is a useful analytic tool for interpreting virtually all complex behavior, and we consider the concepts of derived relations and naming as cases in point.     

401(k) plan asset allocation, account balances, and loan activity in 2010

THE BULK OF 401(K) ASSETS CONTINUED TO BE INVESTED IN STOCKS: On average, at year-end 2010, 62 percent of 401(k) participants' assets were invested in equity securities through equity funds, the equity portion of balanced funds, and company stock. Thirty-three percent were in fixed-income securities such as stable value investments and bond and money funds. SEVENTY PERCENT OF 401(K) PLANS INCLUDED TARGET-DATE FUNDS IN THEIR INVESTMENT LINEUP AT YEAR-END 2010: At year-end 2010, 11 percent of the assets in the EBRI/ICI 401(k) database were invested in target-date funds and 36 percent of 401(k) participants held target-date funds. Also known as lifecycle funds, they are designed to offer a diversified portfolio that automatically rebalances to be more focused on income over time. MORE NEW OR RECENT HIRES INVESTED THEIR 401(K) ASSETS IN BALANCED FUNDS, INCLUDING TARGET-DATE FUNDS: For example, at year-end 2010, 44 percent of the account balances of recently hired participants in their 20s were invested in balanced funds, compared with 42 percent in 2009, and about 7 percent in 1998. A significant subset of that balanced fund category is target-date funds. At year-end 2010, 35 percent of the account balances of recently hired participants in their 20s were invested in target-date funds, compared with 31 percent at year-end 2009. 401(K) PARTICIPANTS CONTINUED TO SEEK DIVERSIFICATION OF THEIR INVESTMENTS: The share of 401(k) accounts invested in company stock continued to shrink, falling by more than a percentage point (to 8 percent) in 2010, continuing a steady decline that started in 1999. Recently hired 401(k) participants contributed to this trend: They tended to be less likely to hold employer stock. PARTICIPANTS' 401(K) LOAN BALANCES DECLINED SLIGHTLY IN 2010: In 2010, 21 percent of all 401(k) participants who were eligible for loans had loans outstanding against their 401(k) accounts, unchanged from year-end 2009, and up from 18 percent at year-end 2008. Loans outstanding amounted to 14 percent of the remaining account balance, on average, at year-end 2010, compared with 15 percent at year-end 2009. Loan amounts outstanding declined slightly from those in the past few years. THE YEAR-END 2010 AVERAGE ACCOUNT BALANCE IN THE DATABASE WAS 3.4 PERCENT HIGHER THAN THE YEAR BEFORE, BUT MAY NOT ACCURATELY REFLECT THE EXPERIENCE OF TYPICAL 401(K) PARTICIPANTS IN 2010: To understand changes in 401(k) participants' average account balances, it is important to analyze a sample of consistent participants. As with previous EBRI/ICI updates, analysis of a sample of consistent 401(k) participants (those that have been in the same plan since 2003) is expected to be published in 2012.