Sleep-Wake Activity Inventory (SWAI) was developed by Rosenthal et al. [8] in 1993, and consists of six subscales evaluating sleepiness, nocturnal sleep, ability to relax, energy level, social desirability, and psychic distress over the previous 7 days [8]. It can evaluate general aspects of sleep and awakening in the patients. SWAI consists of a total of 59 items. Each item is composed of semi-continuous Likert with 1–9 points (1=always, 9=never). SWAI-Excessive daytime sleepiness (EDS) is used for evaluating excessive daytime sleep; a score below 40 indicates excessive sleepiness, a score 50 or above is normal, and a score between 40 and 50 means possible sleepiness. SWAI has well been associated with multiple sleep latency test (MSLT), which are considered the gold standard tests of sleepiness. It is also known to be useful in determining the treatment effect of obstructive sleep apnea (OSA) [9].

Sleep Disorders Questionnaire (SDQ) is a screening tool for evaluation of various sleep disturbances and sleep habits over the previous six months. SDQ was developed by Douglas et al. [10]. It consist of a long questionnaire including 175 items for assessing common sleep disorders such as sleep apnea, narcolepsy, psychiatric sleep disorder, and periodic limb movement disorder over previous six months. Each item can be scored from 1 (never) to 5 (always). SDQ was initially designed to help general practitioners diagnose sleep disorders. The developers have also created a smaller, 45-item version of the scale to assess four common sleep disorders.

The original Dysfunctional Beliefs and Attitudes about Sleep Scale (DBAS) consists of a 30-item self-report questionnaire to evaluate sleep-disruptive cognition. Morin et al. [11] also created a 16-item based brief version of DBAS in 2007. It measures the person’s sleep related cognitions (e.g., faulty beliefs and appraisals, unrealistic expectations, perceptual and attention bias) using 100- mm visual analog scales. A high score indicates a person having extensive false beliefs about sleep. This scale is useful for evaluating an individual’s sleep-related beliefs, attitudes to insomnia, and for evaluating treatment outcomes according to cognitive changes in the patient. A Korean version of DBAS was validated by Yu et al. [12] in 2009.

Pittsburgh Sleep Quality Index (PSQI) was developed by Buysse et al. [13] and is the most widely used tool to evaluate sleep quality and sleep disturbance. It consists of 7 components (subjective sleep quality, sleep latency, sleep duration, habitual sleep efficiency, sleep disturbance, use of sleeping medication, and daytime dysfunction) with a total of 24 items and takes about 5–10 minutes to complete. The 24 items consist of 19 items directly assessed by the patients and 5 items evaluated by the bed partners. Each item is rated from 0 to 3 points, with a total score ranging from 0 to 21 points. If the score is 5 or more, individuals are determined to be bad sleepers; if it is less than 5, they are evaluated as good sleepers. PSQI has been used in the diagnosis of various sleep and insomnia disorders. PSQI was validated as a Korean version [14].

Insomnia Severity Index (ISI) was developed by Morin et al. to evaluate insomnia according to the diagnostic criteria of Diagnostic and Statistical Manual of Mental Disorders, 4th edition and ICSD [15]. ISI is consists of 7 self-reported items (severity of sleep onset, severity of sleep maintenance, severity of early morning awakening problems, sleep dissatisfaction, interference of sleep difficulties with daytime functioning, noticeability of sleep problems by others, distress caused by the sleep difficulties) that assess the nature, severity, and impact of insomnia over the previous month. ISI is rated on a five-point Likert scale from 0 to 4 points per item with a total score of 0–28 points. A score below 7 indicates no insomnia, that between 8 and 14 indicates insomnia below threshold, that between 15 and 21 means moderate insomnia, and that over 22 indicates severe insomnia. It was translated into a Korean version [16]. This questionnaire can be applied to individuals of all ages and is useful for psychiatric patients who have insomnia symptoms.

Epworth Sleepiness Scale (ESS) is a self-rating scale of sleepiness in eight situations developed by Johns [17] and sensitively reflects a person’s sleepiness. In each situation, the degree of sleepiness is assessed from 0 to 3 points, and the total score ranges from 0 to 24 points. A total score of 10 or above indicates a serious case of EDS. It was translated into a Korean version and is widely used in Korean hospitals [18]. Although correlation studies with MSLT are diverse, there are questions about whether ESS can be used as a measure of drowsiness. Because of the Korean unique lifestyle, modifications are necessary to improve the measurement accuracy of the ESS. Most of the respondents were either confused or hesitant to answer certain questions that refer to situations involving sitting and driving. Very recently, Jung et al. [19] developed and validated a modified Korean ESS that reflects the Korean lifestyle.

Stanford Sleepiness Scale (SSS) was developed by Hoddes et al. [20] and is useful for evaluating acute sleepiness through the day. It evaluates the degree of sleepiness and alertness on a scale of 1 to 7 (1=feeling active, vital, alert, and wide awake, 7=almost in reverie and cannot stay awake. Sleep onset is imminent). SSS is very easy to apply, and it can be used several times a day.

Berlin Questionnaire (BQ) was developed by respiratory and primary care physicians through consensus to evaluate OSA, and it was validated in 1996. BQ consists of 10 questions in three categories related to snoring, daytime sleepiness, and obesity or hypertension [21,22]. If positive more than two of the three categories fall into the OSA high-risk group. Category 1 consists of five questions related to snoring and apnea during sleep. It is considered positive when answering yes to 2 or more questions. Category 2 consists of four questions related to sleepiness and tiredness. It is considered positive when answering yes to 2 or more questions. Category 3 is considered positive when the individual has high blood pressure or a BMI >30 kg/m2. BQ was translated into a Korean version [23].

STOP questionnaire was developed by the University of Toronto for screening OSA in 2008 [24]. The eight items including snoring, tiredness during daytime, observed apnea, and high blood pressure are rated as yes or no. Combined with BMI, age, neck size, and gender (STOP-Bang), this questionnaire is useful for patients with moderate to severe OSA.

Calgary Sleep Apnea Quality of Life Index (Calgary SAQLI) was developed by Flemons and Reimer [25] in 1998, and it is a disease-specific quality of life scale for patients with OSA. It evaluates four domains, namely daily functioning (11 questions), social interactions (13 questions), emotional functioning (11 questions), and symptoms of the quality of life (5 questions) that are important to OSA patients. It was designed to be administrated to patients by a trained interviewer. It is rated on a 7-point Likert scale from 1 to 7 points (1=very severe, 7=not at all severe). Calgary SAQLI was translated into a Korean version [26].

Morningness-eveningness refers to individual differences in preferred time of activity during daily life, including circadian rhythm, sleep-wake times, and active time zones. Morningness-Eveningness Questionnaire (MEQ) is the most commonly used self-assessment questionnaire to evaluate individual differences in circadian rhythms and was developed by Horne and Osteberg [27] in 1976. The MEQ is a 19-item questionnaire and the scores range from 16 to 86. A score of 59 or above indicates morningness and a score below 41 indicates eveningness. MEQ was translated into a Korean version.

Composite Scale of Morningness (CSM) was developed by Smith et al. [28] by combining MEQ and Diurnal Type Scale for assessing morningness and eveningness. It consists of 13 questions evaluating an individual’s preferred sleep onset time, wakeup time, and extent of morning or evening activity. Three items are rated from 1 to 4, 10 items are rated from 1 to 5, and the total score ranges from 13 to 55. A score over 49 indicates morning type, and a score less than 26 indicates evening type. CSM was translated into a Korean version in 1997 [29].

Sleep Timing Questionnaire (STQ) was developed by Monk et al. [30] to obtain a patient’s precise sleep schedule and to obtain the individual’s sleep patterns and habits. The questionnaire consists of 18 items; the questions include good night and morning time, number and duration of wake-up during the night, and stability of sleep schedule. STQ has been reported to have a high correlation with actigraphy [30].

International Restless Leg Syndrome Study Group Rating Scale (IRLS) was developed by the International Restless Legs Syndrome Study Group and consists of 10 items to evaluate restless leg syndrome (RLS) symptoms over the previous week [31]. It is designed to evaluate the frequency and severity of RLS, their association with sleep disturbance, daytime functioning, and mood disorder. The degree of severity rated as mild (0 to 10), moderate (11 to 20), severe (21 to 30), and very severe (31 to 40). IRLS was translated into a Korean version in 2010 [32].

The Restless Leg Syndrome Quality of Life Questionnaire (RLSQoL) was designed to assess the quality of life in the patients with RLS over the previous four weeks. It consists of 18 items including daily activities, social activities, concentration, and sexual activities [33]. RLSQoL was also translated into a Korean version in 2010 [32].