Differences In Discounting Research Articles

Age-related differences in delay discounting: Income matters.

Although the authors of a recent meta-analysis concluded there were no age-related differences in the discounting of delayed rewards, they did not examine the effects of income (Seaman et al., 2022). Accordingly, the present study compared discounting by younger and older adults (Ages 35-50 and 65-80) differing in household income. Two procedures were used: the Monetary Choice Questionnaire and the Adjusting-Amount procedure. Whereas no age difference was observed between the higher income (> $80,000) age groups, a significant difference was observed between younger and older adults with lower incomes (< $50,000): The younger adults discounted more steeply than the older adults. These findings, which were observed with both discounting procedures, support our buffering hypothesis, which assumes that the scarcity associated with a lower income is a stressor that can lead to steeper discounting, but that age-related increases in emotional stability can buffer such stressors, leading to age-related differences between lower income age groups. In contrast, no age difference was observed in higher income adults who experience much less scarcity. Further support for the buffering hypothesis comes from the finding that there was no age-related difference in discounting by the lower income groups when distress was statistically controlled. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Choices between money and hyper-palatable food: Choice impulsivity and eating behavior.

Choice impulsivity may influence eating behavior. The study tested whether choice impulsivity, termed delay discounting, may be related to food generally, or may be specific to hyper-palatable foods (HPF). The study also determined whether a discounting task with choices between money and food may have utility in predicting obesity-related outcomes. Participants (N = 284) completed a task that assessed choices between smaller reward available immediately and larger reward available later. Single commodity conditions presented choices between amounts of HPF, non-HPF, or money (e.g., HPF now vs. HPF later). Cross-commodity conditions presented choices between money and food commodities (e.g., money now vs. HPF later; money now vs. non-HPF later). There were no significant differences in discounting of HPF and non-HPF in single commodity conditions (Mean ln[k] difference = .40, p = .058). In the cross-commodity conditions holding money constant as the immediate reward, individuals discounted HPF significantly less than non-HPF (Mean ln[k] difference = .92; p = .0001). In regression analyses, individuals with excess HPF intake, greater HPF craving, and higher BMIs were more likely to choose HPF immediately, when money was the delayed reward (p values = .003 to .008). Choice impulsivity may be specific to foods that are hyper-palatable. Results suggest that individuals with excess HPF intake, higher HPF craving, and higher BMIs may exhibit a general tendency toward impulsive decision making that may be exacerbated in an obesogenic environment that provides wide access to HPF. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Choice Bundling Increases Valuation of Delayed Losses More Than Gains in Cigarette Smokers.

Choice bundling, in which a single choice produces a series of repeating consequences over time, increases valuation of delayed monetary and non-monetary gains. Interventions derived from this manipulation may be an effective method for mitigating the elevated delay discounting rates observed in cigarette smokers. No prior work, however, has investigated whether the effects of choice bundling generalize to reward losses. In the present study, an online panel of cigarette smokers (N = 302), recruited using survey firms Ipsos and InnovateMR, completed assessments for either monetary gains or losses (randomly assigned). In Step 1, participants completed a delay-discounting task to establish Effective Delay 50 (ED50), or the delay required for an outcome to lose half of its value. In Step 2, participants completed three conditions of an adjusting-amount task, choosing between a smaller, sooner (SS) adjusting amount and a larger, later (LL) fixed amount. The bundle size (i.e., number of consequences) was manipulated across conditions, where a single choice produced either 1 (control), 3, or 9 consequences over time (ascending/descending order counterbalanced). The delay to the first LL amount in each condition, as well as the intervals between all additional SS and LL amounts (where applicable), were set to individual participants’ ED50 values from Step 1 to control for differences in discounting of gains and losses. Results from Step 1 showed significantly higher ED50 values (i.e., less discounting) for losses compared to gains (p < 0.001). Results from Step 2 showed that choice bundling significantly increased valuation of both LL gains and losses (p < 0.001), although effects were significantly greater for losses (p < 0.01). Sensitivity analyses replicated these conclusions. Future research should examine the potential clinical utility of choice bundling, such as development of motivational interventions that emphasize both the bundled health gains associated with smoking cessation and the health losses associated with continued smoking.

Smoking, hazardous drinking and individual differences in cost and gain discounting.

Aims:Past research has linked substance use to individual differences in discounting of future rewards. Since behaviours such as smoking and excessive drinking appear to involve a devaluation of future negative consequences, discounting of costs may also be relevant in the understanding of such behaviour. The primary aims were to investigate the association between cost discounting and the behaviours smoking and hazardous drinking.Methods:In four studies, individuals recruited from the crowdsourcing marketplace Amazon Mechanical Turk responded to measures of discounting. Results were combined by meta-analysis of the standardised mean differences (d) between self-reported smokers and non-smokers, and between participants with AUDIT scores of 10+ (hazardous drinking) and those with scores below 10.Results:In comparison with non-smokers, smokers’ relative valuations of future gains were lower, d = –0.32, 95% CI [–0.47, –0.18]. There was no association between smoking and cost discounting, d = –0.02, 95% CI [–0.17, 0.13]. Participants with AUDIT scores of 10+ valued future gains somewhat lower than participants with scores below 10, d = –0.17, 95% CI [–0.35, 0.01]. There was no association between hazardous drinking and cost discounting, d = –0.02, 95% CI [–0.21, 0.16]. According to Bayes Factors (BF), the data supported an association between gain discounting and smoking (BF > 100). It was insensitive in the analysis of gain discounting and hazardous drinking (BF = 0.6), but it strongly supported null-effects in both analyses of cost discounting (BFs = 0.1).Conclusion:The results suggest that the robust link between gain discounting and smoking status does not reflect a general devaluation of future outcomes among smokers.

Frontotemporal Regulation of Subjective Value to Suppress Impulsivity in Intertemporal Choices.

Impulsive decisions arise from preferring smaller but sooner rewards compared with larger but later rewards. How neural activity and attention to choice alternatives contribute to reward decisions during temporal discounting is not clear. Here we probed (1) attention to and (2) neural representation of delay and reward information in humans (both sexes) engaged in choices. We studied behavioral and frequency-specific dynamics supporting impulsive decisions on a fine-grained temporal scale using eye tracking and MEG recordings. In one condition, participants had to decide for themselves but pretended to decide for their best friend in a second prosocial condition, which required perspective taking. Hence, conditions varied in the value for themselves versus that pretending to choose for another person. Stronger impulsivity was reliably found across three independent groups for prosocial decisions. Eye tracking revealed a systematic shift of attention from the delay to the reward information and differences in eye tracking between conditions predicted differences in discounting. High-frequency activity (175-250 Hz) distributed over right frontotemporal sensors correlated with delay and reward information in consecutive temporal intervals for high value decisions for oneself but not the friend. Collectively, the results imply that the high-frequency activity recorded over frontotemporal MEG sensors plays a critical role in choice option integration.SIGNIFICANCE STATEMENT Humans face decisions between sooner smaller rewards and larger later rewards daily. An objective benefit of losing weight over a longer time might be devalued in face of ice cream because they prefer currently available options because of insufficiently considering long-term alternatives. The degree of contribution of neural representation and attention to choice alternatives is not clear. We investigated correlates of such decisions in participants deciding for themselves or pretending to choose for a friend. Behaviorally participants discounted less in self-choices compared with the prosocial condition. Eye movement and MEG recordings revealed how participants represent choice options most evident for options with high subjective value. These results advance our understanding of neural mechanisms underlying decision-making in humans.

Gain–Loss Asymmetry in Experiential Probability Discounting

Probability discounting is loss in reinforcer value as a function of uncertainty. In typical tasks measuring probability discounting, participants repeatedly choose between a smaller, certain amount and a larger amount at one of several probabilities, and do not experience the outcome they select. Most participants show a gain–loss asymmetry, discounting gains more steeply than losses. We examined whether gain–loss asymmetry also occurred when participants received feedback about the number of points they had gained or lost following choices, and whether discounting rates changed as participants accrued experience of outcomes across the session. We assessed discounting of hypothetical monetary gains and losses twice using a mixed description-experience task. In these tasks, participants chose repeatedly between options that were described, where each choice was then followed by feedback on the number of points gained or lost from the chosen option, but not the unchosen option (i.e. a partial feedback procedure). Neither the first nor second task showed a consistent mean difference in discounting of gains and losses. Discounting in the first task was affected by an interaction of condition order and type of outcome (gains or losses). Furthermore, discounting of losses was more stable across task administrations than discounting of gains. Participants’ tendency to choose the probabilistic option was significantly correlated across conditions. Together, this highlights the crucial role of recent experience of outcomes on probability discounting of gains and losses.

Individual Differences in Dopamine Are Associated with Reward Discounting in Clinical Groups But Not in Healthy Adults.

Some people are more willing to make immediate, risky, or costly reward-focused choices than others, which has been hypothesized to be associated with individual differences in dopamine (DA) function. In two studies using PET imaging, one empirical (Study 1: N = 144 males and females across 3 samples) and one meta-analytic (Study 2: N = 307 across 12 samples), we sought to characterize associations between individual differences in DA and time, probability, and physical effort discounting in human adults. Study 1 demonstrated that individual differences in DA D2-like receptors were not associated with time or probability discounting of monetary rewards in healthy humans, and associations with physical effort discounting were inconsistent across adults of different ages. Meta-analytic results for temporal discounting corroborated our empirical finding for minimal effect of DA measures on discounting in healthy individuals but suggested that associations between individual differences in DA and reward discounting depend on clinical features. Addictions were characterized by negative correlations between DA and discounting, but other clinical conditions, such as Parkinson's disease, obesity, and attention-deficit/hyperactivity disorder, were characterized by positive correlations between DA and discounting. Together, the results suggest that trait differences in discounting in healthy adults do not appear to be strongly associated with individual differences in D2-like receptors. The difference in meta-analytic correlation effects between healthy controls and individuals with psychopathology suggests that individual difference findings related to DA and reward discounting in clinical samples may not be reliably generalized to healthy controls, and vice versa.SIGNIFICANCE STATEMENT Decisions to forgo large rewards for smaller ones due to increasing time delays, uncertainty, or physical effort have been linked to differences in dopamine (DA) function, which is disrupted in some forms of psychopathology. It remains unclear whether alterations in DA function associated with psychopathology also extend to explaining associations between DA function and decision making in healthy individuals. We show that individual differences in DA D2 receptor availability are not consistently related to monetary discounting of time, probability, or physical effort in healthy individuals across a broad age range. By contrast, we suggest that psychopathology accounts for observed inconsistencies in the relationship between measures of DA function and reward discounting behavior.

Assessing individual differences in discounting: Construction and initial validation of the Discounting Inventory

The purpose of the project was to develop the Discounting Inventory (DI), a measure of individual differences in delay, probability, effort, and social discounting, all related to behavioral impulsivity. Over 400 items relating to four types of discounting were generated. Next, a study followed by a series of psychometric analyses of data obtained from a group of 2843 individuals was conducted. Principal Component Analysis yielded a four-factor structure of data, reflecting the four types of discounting. The results of Confirmatory Factor Analysis showed good fit of the four-factor model to data. Through several iterations of retaining and deleting items on the basis of their component loadings, item intercorrelations, and contribution to coefficient alphas, the total number of items was reduced to 48. The final 48-item version of the inventory has satisfactory psychometric characteristics, including Cronbach’s alpha and test–retest stability. In addition, significant correlations were observed between the DI and traditional discounting instruments, suggesting that the DI measures a construct similar to the behavioral discounting process. The development of the tool was based on the assumption that discounting is a personality trait. However, the present data suggest that discounting may reflect more a state than trait function.

A second type of magnitude effect: Reinforcer magnitude differentiates delay discounting between substance users and controls.

Basic research on delay discounting, examining preference for smaller-sooner or larger-later reinforcers, has demonstrated a variety of findings of considerable generality. One of these, the magnitude effect, is the observation that individuals tend to exhibit greater preference for the immediate with smaller magnitude reinforcers. Delay discounting has also proved to be a useful marker of addiction, as demonstrated by the highly replicated finding of greater discounting rates in substance users compared to controls. However, some research on delay discounting rates in substance users, particularly research examining discounting of small-magnitude reinforcers, has not found significant differences compared to controls. Here, we hypothesize that the magnitude effect could produce ceiling effects at small magnitudes, thus obscuring differences in delay discounting between groups. We examined differences in discounting between high-risk substance users and controls over a broad range of magnitudes of monetary amounts ($0.10, $1.00, $10.00, $100.00, and $1000.00) in 116 Amazon Mechanical Turk workers. We found no significant differences in discounting rates between users and controls at the smallest reinforcer magnitudes ($0.10 and $1.00) and further found that differences became more pronounced as magnitudes increased. These results provide an understanding of a second form of the magnitude effect: That is, differences in discounting between populations can become more evident as a function of reinforcer magnitude.

Male, But Not Female, Alcohol-Dependent African Americans Discount Delayed Gains More Steeply than Propensity-Score Matched Controls.

Alcohol dependence is known to be associated with steep discounting of delayed rewards, but its relation to the discounting of delayed losses and probabilistic rewards is unclear. Moreover, patterns of alcohol consumption vary considerably between communities, but previous research has not examined the relation between discounting and alcohol dependence in low-income African Americans. The goal of the present study was to determine whether low-income, alcohol-dependent African Americans differ from controls in the degree to which they discount delayed rewards, delayed losses, or probabilistic rewards. African-American participants, both cases and controls, were recruited from the same low-income neighborhoods, and propensity-score matching was used to further control for demographic differences. Participants performed three tasks that assessed their discounting of hypothetical monetary outcomes: delayed rewards, delayed losses, and probabilistic rewards. Alcohol-dependent cases discounted delayed gains, but not delayed losses or probabilistic gains, more steeply than their matched controls. The difference in discounting of delayed gains was localized to the male cases, whose discounting was steeper than either the male controls or the female cases; no gender difference was observed between male and female controls. The present results extend findings regarding discounting by substance abusers to a previously unstudied group, low-income African Americans, and suggest that in this group at least, alcohol dependence, particularly in males, may be more a reflection of choosing immediate rewards than of ignoring their delayed negative consequences.

Opportunity costs of reward delays and the discounting of hypothetical money and cigarettes

Humans are reported to discount delayed rewards at lower rates than nonhumans. However, nonhumans are studied in tasks that restrict reinforcement during delays, whereas humans are typically studied in tasks that do not restrict reinforcement during delays. In nonhuman tasks, the opportunity cost of restricted reinforcement during delays may increase delay discounting rates. The present within-subjects study used online crowdsourcing (Amazon Mechanical Turk, or MTurk) to assess the discounting of hypothetical delayed money (and cigarettes in smokers) under four hypothetical framing conditions differing in the availability of reinforcement during delays. At one extreme, participants were free to leave their computer without returning, and engage in any behavior during reward delays (modeling typical human tasks). At the opposite extreme, participants were required to stay at their computer and engage in little other behavior during reward delays (modeling typical nonhuman tasks). Discounting rates increased as an orderly function of opportunity cost. Results also indicated predominantly hyperbolic discounting, the "magnitude effect," steeper discounting of cigarettes than money, and positive correlations between discounting rates of these commodities. This is the first study to test the effects of opportunity costs on discounting, and suggests that procedural differences may partially account for observed species differences in discounting.

Discounting of delayed rewards: (A)theoretical interpretation of the Kirby questionnaire

111 Participants, recruited from Amazon's MTurk worker pool, completed Kirby's (2009) monetary choice questionnaire, which involves choosing between immediate, but smaller rewards and delayed, but larger rewards. Individual participants’ responses were scored in three ways: first, by calculating the proportion of choices of the delayed rewards; second; using the scoring procedure described by Kirby et al. (1999) to estimate discounting rate (i.e., the value of the k-parameter in a hyperbolic discounting function); and third, using logistic regression to estimate discounting rate (Wileyto et al., 2004). Individuals’ scores calculated using the proportion measure and the logarithms of their estimated k values were very strongly correlated (rs>.97). In addition, the proportions of choices of small, medium, and large amounts of the delayed rewards were strongly correlated (rs>.80). Taken together, these results suggest that the relative ease of calculating the proportion measure does not require sacrificing reliability. Moreover, the proportion measure is atheoretical and very easy to calculate whereas estimating an individual's discounting rate requires assuming a theoretical model that may not be appropriate. Significant differences in the proportion of delayed reward choices were observed between the small, medium, and large delayed reward amounts, with smaller rewards being discounted more steeply than larger ones, replicating previous findings of magnitude effects. These results provide further validation of the proportion of delayed reward choices on the Kirby questionnaire as a measure of individual and group differences in discounting.

Delay Discounting of Oral Morphine and Sweetened Juice Rewards in Dependent and Non-Dependent Rats

Opioid-dependent humans are reported to show accelerated delay discounting of opioid rewards when compared to monetary rewards. It has been suggested that this may reflect a difference in discounting of consumable and non-consumable goods not specific to dependent individuals. Here, we evaluate the discounting of similar morphine and non-morphine oral rewards in dependent and non-dependent rats We first tested the analgesic and rewarding effects of our morphine solution. In a second experiment, we assigned rats randomly to either dependent or non-dependent groups that, 30min after daily testing, received 30mg/kg subcutaneous dose of morphine, or saline, respectively. Delay discounting of drug-free reward was examined prior to initiation of the dosing regimen. We tested discounting of the morphine reward in half the rats and retested the discounting of the drug-free reward in the other half. All tests were run 22.5h after the daily maintenance dose. Rats preferred the morphine cocktail to the drug-free solution and consumed enough to induce significant analgesia. The control quinine solution did not produce these effects. Dependent rats discounted morphine rewards more rapidly than before dependence and when compared to discounting drug-free rewards. In non-dependent rats both reward types were discounted similarly. These results show that morphine dependence increases impulsiveness specifically towards a drug reward while morphine experience without dependence does not.

Increased functional coupling between the left fronto‐parietal network and anterior insula predicts steeper delay discounting in smokers

In previous work, smokers showed steeper devaluation of delayed rewards than non-smokers. While the neural correlates of this link between nicotine dependence and delay of discounting are not established, altered activity in executive networks may relate to impaired delayed gratification. The goal of this study was to examine neural correlates of discounting and their relation to nicotine dependence. Thirty-nine smokers and 33 non-smokers completed a functional magnetic resonance imaging (fMRI) intertemporal choice task in which they made individualized Hard (similarly valued), easy (dissimilarly valued), and control monetary choices. FMRI data were analyzed using a group independent component analysis and dual regression. Smokers discounted more steeply than non-smokers, although this difference was only significant among severely dependent smokers. Intertemporal choices recruited distinct left- and right-lateralized fronto-parietal networks. A group-by-difficulty interaction indicated that smokers, relative to non-smokers, exhibited less difficulty-sensitivity in the right fronto-parietal network. In contrast, smokers showed greater functional connectivity between the left fronto-parietal network and the left fronto-insular cortex. Moreover, the degree of functional connectivity between the left fronto-parietal network and left fronto-insular cortex was significantly correlated with individual differences in discounting. Thus, greater functional coupling between the anterior insula and left fronto-parietal network is a candidate neural substrate linking smoking and impulsivity. Given the anterior insula's role in interfacing cognitive and interoceptive processing, this altered functional connectivity may relate to an addiction-related bias towards immediate rewards.

Neuroeconomics and Adolescent Substance Abuse: Individual Differences in Neural Networks and Delay Discounting

Many adolescents with substance use problems show poor response to evidence-based treatments. Treatment outcome has been associated with individual differences in impulsive decision making as reflected by delay discounting (DD) rates (preference for immediate rewards). Adolescents with higher rates of DD were expected to show greater neural activation in brain regions mediating impulsive/habitual behavioral choices and less activation inregions mediating reflective/executive behavioral choices. Thirty adolescents being treated for substance abuse completed a DD task optimized to balance choices of immediate versus delayed rewards, and a control condition accounted for activation during magnitude valuation. A group independent component analysis on functional magnetic resonance imaging time courses identified neural networks engaged during DD. Network activity was correlated with individual differences in discounting rate. Higher discounting rates were associated with diminished engagement of an executive attention control network involving the dorsolateral prefrontal cortex, dorsomedial prefrontal cortex, inferior parietal cortex, cingulate cortex, and precuneus. Higher discounting rates also were associated with less deactivation in a "bottom-up" reward valuation network involving the amygdala, hippocampus, insula, and ventromedial prefrontal cortex. These 2 networks were significantly negatively correlated. Results support relations between competing executive and reward valuation neural networks and temporal decision making, an important, potentially modifiable risk factor relevant for the prevention and treatment of adolescent substance abuse. Clinical trial registration information-The Neuroeconomics of Behavioral Therapies for Adolescent Substance Abuse, http://clinicaltrials.gov/, NCT01093898.

The neural basis of cultural differences in delay discounting.

People generally prefer to receive rewarding outcomes sooner rather than later. Such preferences result from delay discounting, or the process by which outcomes are devalued for the expected delay until their receipt. We investigated cultural differences in delay discounting by contrasting behaviour and brain activity in separate cohorts of Western (American) and Eastern (Korean) subjects. Consistent with previous reports, we find a dramatic difference in discounting behaviour, with Americans displaying much greater present bias and elevated discount rates. Recent neuroimaging findings suggest that differences in discounting may arise from differential involvement of either brain reward areas or regions in the prefrontal and parietal cortices associated with cognitive control. We find that the ventral striatum is more greatly recruited in Americans relative to Koreans when discounting future rewards, but there is no difference in prefrontal or parietal activity. This suggests that a cultural difference in emotional responsivity underlies the observed behavioural effect. We discuss the implications of this research for strategic interrelations between Easterners and Westerners.

Differences in delay discounting between smokers and nonsmokers remain when both rewards are delayed

When offered a choice between a small monetary reward available immediately (SmallNow) versus a larger reward available after a delay (LargeLater), smokers select the SmallNow alternative more than nonsmokers. That is, smokers discount the value of the LargeLater reward more than nonsmokers. To investigate whether this group difference was due to smokers overweighting the value of rewards available immediately compared with nonsmokers, we examined whether the group difference was also seen when both alternatives were delayed, i.e., when choosing between a SmallSoon reward and a LargeLater reward. In Experiment 1, smokers and nonsmokers completed a task including SmallNow versus LargeLater choices and SmallSoon versus LargeLater choices. In Experiment 2, smokers and nonsmokers completed the same task but with hypothetical choices. Analyses using hyperbolic and double exponential (β-δ) models replicate prior findings that smokers discount the LargeLater reward more than nonsmokers when the smaller reward is available immediately. The smoker-nonsmoker difference was also seen when the smaller reward was slightly delayed, though this effect was primarily driven by heightened discounting in male smokers. However, for potentially real rewards only, this smoker-nonsmoker difference was significantly reduced when the smaller reward was delayed. The smoker-nonsmoker difference in discounting is not confined to situations involving immediate rewards. Differences associated with potentially real versus hypothetical rewards and gender underscore the complexity of the smoking-delay discounting relationship.

Individual differences in discount rate are associated with demand for self‐administered cocaine, but not sucrose

Substance abusers, including cocaine abusers, discount delayed rewards to a greater extent than do matched controls. In the current experiment, individual differences in discounting of delayed rewards in rats (choice of one immediate over three delayed sucrose pellets) were assessed for associations with demand for either sucrose pellets or an intravenous dose of 0.1 mg/kg/infusion cocaine. Twenty-four male Sprague Dawley rats were split into three groups based on sensitivity to delay to reinforcement. Then, demand for sucrose pellets and cocaine was determined across a range of fixed-ratio values. Delay discounting was then reassessed to determine the stability of this measure over the course of the experiment. Individual differences in impulsive choice were positively associated with elasticity of demand for cocaine, a measure of reinforcer value, indicating that rats having higher discount rates also valued cocaine more. Impulsive choice was not associated with the level of cocaine consumption as price approached 0 or with any parameter associated with demand for sucrose. Individual sensitivity to delay was correlated with the initial assessment when reassessed at the end of the experiment, although impulsive choice increased for this cohort of rats as a whole. These findings suggest that impulsive choice in rats is positively associated with valuation of cocaine, but not sucrose.

Temperament and the Discounting of Delayed and Probabilistic Rewards

The present study attempts to combine the more European tradition of studying temperament and individual differences with the more North American tradition of functionalism and behavior analysis by examining the relationship between several temperamental traits (sensation seeking, extraversion, and impulsivity) and discounting of delayed and probabilistic rewards. To evaluate discounting of delayed rewards, participants chose between hypothetical immediate monetary rewards and larger amounts that could be obtained after a specified delay. To evaluate discounting of probabilistic rewards, participants chose between monetary rewards that were certain and larger amounts that could be obtained with a specified probability. Hyperbolic functions described well the discounting of both delayed and probabilistic rewards for all groups of participants. The rate at which delayed rewards were discounted was related to extraversion and impulsivity, but not to the sensation-seeking dimension. Both extraverts and high impulsive individuals showed higher temporal discounting rates than introverts and low impulsive individuals. Differences in their subjective perception of time might account for the different rates of discounting between these groups. On the other hand, the rate at which probabilistic rewards were discounted did not differ between high and law impulsive participants, nor between introverts and extraverts. That temperament was related to differences in discounting of delayed but not probabilistic rewards in extraverts versus introverts and high versus low impulsive participants suggests that, although the same mathematical function describes both forms of discounting in all groups, delay and probability might not be functionally equivalent.

The Small Firms Effect on New Issues of Common Stocks When Listing Requirements Differ Between Exchanges

This paper extends the search for small firms and exchange efficiency effects on seasoned stocks to the new issues market on a sample of placings drawn from the UKs Official List, Unlisted Securities Market and Third Market. Tests of means and regressions are undertaken to examine the relationships between sizes of new issues discounts, sizes of firms, and the exchange on which their equities are traded. Despite the observation that new issues discounts tend to be larger for equities of firms traded on exchanges with lower listing requirements, there is little evidence that the differences in discounts are affected by firm size.