BootES: an R package for bootstrap confidence intervals on effect sizes.

Bootstrap Effect Sizes (bootES; Gerlanc & Kirby, 2012) is a free, open-source software package for R (R Development Core Team, 2012), which is a language and environment for statistical computing. BootES computes both unstandardized and standardized effect sizes (such as Cohen's d, Hedges's g, and Pearson's r) and makes easily available for the first time the computation of their bootstrap confidence intervals (CIs). In this article, we illustrate how to use bootES to find effect sizes for contrasts in between-subjects, within-subjects, and mixed factorial designs and to find bootstrap CIs for correlations and differences between correlations.

An empirical assessment of the form of utility functions.

Utility functions, which relate subjective value to physical attributes of experience, are fundamental to most decision theories. Seven experiments were conducted to test predictions of the most widely assumed mathematical forms of utility (power, log, and negative exponential), and a function proposed by Rachlin (1992). For pairs of gambles for real monetary gains, undergraduate and nonstudent subjects either reported an equalizing amount for 1 outcome that made the gambles subjectively equal or chose between gambles where the amounts were varied across trial, which allowed the equalizing amount to be estimated from their pattern of choices.

The hierarchical structure of self-reported impulsivity.

The hierarchical structure of 95 self-reported impulsivity items, along with delay-discount rates for money, was examined. A large sample of college students participated in the study (N = 407). Items represented every previously proposed dimension of self-reported impulsivity.

One-year temporal stability of delay-discount rates.

The temporal stability of delay-discount rates for monetary rewards was assessed using a monetary choice questionnaire (Kirby & Marakovic, 1996). Of 100 undergraduate participants who completed the questionnaire at the initial session, 81 returned 5 weeks later and 46 returned 57 weeks later for subsequent sessions. The 5-week test-retest stability of discount rates was .

The present values of delayed rewards are approximately additive.

In two experiments, human subjects were asked to estimate their present values of single delayed rewards and their present values of temporal sequences of three rewards. Present values were solicited by asking subjects to indicate an amount of money v for which they would be indifferent between receiving v at the end of the session and receiving the delayed reward(s). A procedure was used for which responding the true value of v was the optimal strategy, and the actual payoff that each subject received was determined by one randomly selected trial.

Heroin and cocaine abusers have higher discount rates for delayed rewards than alcoholics or non-drug-using controls.

Aims: To test a prediction of the discounting model of impulsiveness that discount rates would be positively associated with addiction. The delay-discount rate refers to the rate of reduction in the present value of a future reward as the delay to that reward increases.

Design And Measurements: We estimated participants' discount rates on the basis of their pattern of choices between smaller immediate rewards ($11-80) and larger, delayed rewards ($25-85; at delays from 1 week to 6 months) in a questionnaire format.

Concave utility, transaction costs, and risk in measuring discounting of delayed rewards.

Research has consistently found that the decline in the present values of delayed rewards as delay increases is better fit by hyperbolic than by exponential delay-discounting functions. However, concave utility, transaction costs, and risk each could produce hyperbolic-looking data, even when the underlying discounting function is exponential. In Experiments 1 (N = 45) and 2 (N = 103), participants placed bids indicating their present values of real future monetary rewards in computer-based 2nd-price auctions.

Effects of gender and family history of alcohol dependence on a behavioral task of impulsivity in healthy subjects.

Objective: Substance misusers are often considered impulsive, but it is unclear whether impulsivity precedes substance misuse or develops as a consequence of it. Because alcohol dependence has a clear familial component, a study comparing impulsivity in nonaffected individuals who differ with respect to paternal history of alcohol dependence may provide evidence of familial vulnerability to impulsivity.

Method: 122 healthy individuals participated, none of whom misused alcohol or drugs; 58 were paternal history positive (PHP) and 64 were paternal history negative (PHN) for alcohol dependence.