On some trials, a stop signal is presented just prior to, or simultaneously with the go signal, and the subject must inhibit the impending response. The SSRT test is similar, except that the stop signal is presented after the go signal. This small modification increases the difficulty of inhibiting the go response, because the participant has typically already initiated the go response by the time the stop signal is presented. The participant is instructed to respond as fast as possible to the go signal while maintaining the highest possible inhibition accuracy (on no-go trials). During the task, the time at which the stop signal is presented (the stop signal delay or SSD) is dynamically adjusted to match the time after the go signal at which the participant is just able/unable to inhibit their go response. If the participant fails to inhibit their go response, the stop signal is moved slightly closer to the original go signal, and if the participant successfully inhibits their go response, the stop signal is moved slightly ahead in time. The SSRT is thus measured as the average go response time minus the average stop signal presentation time (SSD). Balloon Analogue Risk Task
The balloon analogue risk task (BART) was designed to assess risk-taking behavior. Subjects are presented with a computer depiction of a balloon that can be incrementally inflated by pressing a response key. As the balloon inflates, the subject accumulates rewards with each new key-press. The balloon is programmed with a constant probability of popping.
Other manifestations primarily of impulsivity include
being very impatient, 
having difficulty waiting for things they want or waiting their turns in games, 
often interrupting conversations or others activities, or
blurting out inappropriate comments, showing their emotions without restraint, and act without regard for consequences. Prevalence of the disorder worldwide is estimated to be between 4% and 10%, with reports as low as 2.2% and as high as 17.8%. Variation in rate of diagnoses may be attributed to differences between populations (i.e. culture), and differences in diagnostic methodologies. Prevalence of ADHD among females is less than half that of males, and females more commonly fall into the inattentive subtype.Despite an upward trend in diagnoses of the inattentive subtype of ADHD, impulsivity is commonly considered to be the central feature of ADHD, and the impulsive and combined subtypes are the major contributors to the societal costs associated with ADHD. The estimated cost of illness for a child with ADHD is $14,576 (in 2005 dollars) annually. Prevalence of ADHD among prison populations is significantly higher than that of the normal population.In both adults and children, ADHD has a high rate of comorbidity with other mental health disorders such as learning disability, conduct disorder, anxiety disorder, major depressive disorder, bipolar disorder, and substance use disorders. The precise genetic and environmental factors contributing to ADHD are relatively unknown, but endophenotypes offer a potential middle ground between genes and symptoms. ADHD is commonly linked to "core" deficits involving "executive function," "delay aversion," or "activation/arousal" theories that attempt to explain ADHD through its symptomology.