in the evening. dspd-friendly careers can include security work, the entertainment industry, hospitality work in restaurants, theaters, hotels or bars, call center work, manufacturing, healthcare or emergency medicine, commercial cleaning, taxi or truck driving, the media, and freelance writing, translation, it work, or medical transcription. some other careers that have an emphasis on early morning work hours, such as bakers, coffee baristas, pilots and flight crews, teachers, mail carriers, waste collection, and farming, can be particularly difficult for people who naturally sleep later than is typical. some careers, such as over-the-road truck drivers, firefighters, law enforcement, nursing, can be suitable for both people with delayed sleep phase syndrome and people with the opposite condition, advanced sleep phase disorder, as these workers are needed both very early in the morning and also late at night. some people with the disorder are unable to adapt to earlier sleeping times, even after many years of treatment. sleep researchers dagan and abadi have proposed that the existence of untreatable cases of dspd be formally recognized as a "sleep-wake schedule disorder (swsd) disability", an invisible disability. rehabilitation for dspd patients includes acceptance of the condition and choosing a career that allows late sleeping times or running a home business with flexible hours. in a few schools and universities, students with dspd have been able to arrange to take exams at times of day when their concentration levels may be good. patients suffering from swsd disability should be encouraged to accept the fact that they suffer from a permanent disability, and that their quality of life can only be improved if they are willing to undergo rehabilitation. it is imperative that physicians recognize the medical condition of swsd disability in their patients and bring it to the notice of the public institutions responsible for vocational and social rehabilitation. in the united states, the americans with disabilities act requires that employers make reasonable accommodations for employees with sleeping disorders. in the case of dspd, this may require that the employer accommodate later working hours for jobs normally performed on a "9 to 5" work schedule. the statute defines "disability" as a "physical or mental impairment that substantially limits one or more major life activities", and section 12102(2)(a) itemizes sleeping as a "major life activity". impact on patients lack of public awareness of the disorder contributes to the difficulties experienced by people with dspd, who are commonly stereotyped as undisciplined or lazy. parents may be chastised for not giving their children acceptable sleep patterns, and schools and workplaces rarely tolerate chronically late, absent, or sleepy students and workers, failing to see them as having a chronic condition. by the time dspd sufferers receive an accurate diagnosis, they often have been misdiagnosed or labelled as lazy and incompetent workers or students for years. misdiagnosis of circadian rhythm sleep disorders as psychiatric conditions causes considerable distress to patients and their families, and leads to some patients being inappropriately prescribed psychoactive drugs. for many patients, diagnosis of dspd is itself a life-changing breakthrough. as dspd is so little-known and so misunderstood, peer support may be important for information, self-acceptance, and future research studies. people with dspd who force themselves to follow a normal 9–5 workday "are not often successful and may develop physical and psychological complaints during waking hours, e.g., sleepiness, fatigue, headache, decreased appetite, or depressed mood. patients with circadian rhythm sleep disorders often have difficulty maintaining ordinary social lives, and some of them lose their jobs or fail to attend school." epidemiology there have been several studies that have attempted to estimate the prevalence of dspd. results vary due to differences in methods of data collection and diagnostic criteria. a particular issue is where to draw the line between extreme evening chronotypes and clinical dspd. using the icsd-1 diagnostic criteria (current edition icsd-3) a study by telephone questionnaire in 1993 of 7,700 randomly selected adults (aged 18–67) in norway estimated the prevalence of dspd at 0.17%. a similar study in 1999 of 1,525 adults (aged 15–59) in japan estimated its prevalence at 0.13%. a somewhat higher prevalence of 0.7% was found in a 1995 san diego study. a 2014 study of 9100 new zealand adults (age 20–59) using a modified version of the munich chronotype questionnaire found a dspd prevalence of 1.5% to 8.9% depending on the strictness of the definition used. a 2002 study of older adults (age 40–65) in san diego found 3.1% had complaints of difficulty falling asleep at night and waking in the morning, but did not apply formal diagnostic criteria. actimetry readings showed only a small proportion of this sample had delays of sleep timing. a marked delay of sleep patterns is a normal feature of the development of adolescent humans. according to mary carskadon, both circadian phase and homeostasis (the accumulation of sleep pressure during the wake period) contribute to a dspd-like condition in post-pubertal as compared to pre-pubertal youngsters. adolescent sleep phase delay "is present both across cultures and across mammalian species" and "it seems to be related to pubertal stage rather than age." as a result, diagnosable dspd is much more prevalent among adolescents. with estimates ranging from 3.4% to 8.4% among high school students.