THE SLEEP DIAGNOSIS LIST (SDL): A QUESTIONNAIRE FOR SCREENING GENERAL SLEEP DISORDERS

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1 THE SLEEP DIAGNOSIS LIST (SDL): A QUESTIONNAIRE FOR SCREENING GENERAL SLEEP DISORDERS Sweere Y 1, Kerkhof GA 2, De Weerd AW 1, Kamphuisen HAC 1, Kemp B 1 & Schimsheimer RJ 1 1 Centre for Sleep and Wake Disorders Westeinde Hospital, The Hague, The Netherlands 2 Department of Physiology and Psychology, University of Leiden, The Netherlands INTRODUCTION The Sleep Diagnosis List (SDL) is a diagnostic questionnaire consisting of 89 items which can be answered on a 5 level-scale. The SDL is a derivation of the Sleep Disorders Questionnaire (SDQ), published by Douglass et al (1). Use of the SDQ has many objections. First, the SDQ consist of 175 items which make testing time long. Second, patients are only assessed on the basis of four sleep disorders scales (sleep apnea syndrome, narcolepsy, psychiatric sleep disorder and periodic movement of the limb syndrome). Third, the periodic movement of the limb scale has proven very weak; it seems to measure insomnia rather than a specific sleep disorder such as periodic movement of the limbs (2). The present investigation was concerned with the internal structure and homogeneity of the new questionnaire, the SDL. PATIENTS AND METHODS Derivation of the SDL was accomplished by a combination of empirical methods and clinical judgement. First, all SDQ-items were eliminated that were judged to be of minor clinical relevance. In addition, a principal components analysis was performed, and items with a low factor loading were also excluded. New items regarding insomnia, the periodic limb movement disorder and psychiatric sleep disorders were added. To examine the underlying structure of the SDL, a principal component analysis was performed. The resulting principal components were submitted to a Cronbach s alpha procedure to test for homogeneity. A total of 746 questionnaires were used which were filled out by patients who visited the Centre for Sleep and Wake Disorders. Participants included 274 women and 472 men. Their average age was (SD = 13.48, range 7-83 year). RESULTS The principal components analysis yielded 19 factors (principal components) with an eigen value greater than 1. Thirteen of these are relevant and jointly account for 117

2 58.3 % of total variance. Table 1 presents the Varimax-rotated factor structure. It includes all factors with a loading (correlation between the item and the factor) of > 0.4. Next to factor loading, a description of the corresponding item is given. In addition, the percentages explained variance of the factors are shown. Table 2 shows the internal consistency (Cronbach s alpha) of each factor. Table 1: Varimax rotated factor structure Factor loading Item description Explained variance Factor 1 Insomnia 19.6%.81 poor night s sleep.79 trouble getting back to sleep after awakening.76 too little sleep at night.73 early morinig awakening.73 light sleep.70 wake up often.64 unable to sleep for nights.63 trouble getting to sleep.59 staying in bed and trying harder.58 afraid of not being able to go to sleep.56 feeling suddenly awake when going to bed.49 becoming angry when not falling asleep quickly.47 muscular tension at bedtime.45 restless sleep.41 worrying about the sleep problem Factor 2 Psychiatry 9.6%.79 being nervous and tensed.72 feeling gloomy and depressed.72 troubled by tensions and stress.70 worrying in bed.70 feeling uneasy.69 sad and depressed feelings at bedtime.62 feeling anxious.60 easily in panic.60 racing thoughts in bed.56 feeling useless and not needed.51 having crying spells.47 unhappy about social life.45 considered or attempted suicide 118

3 Factor 3 Restless legs 5.7%.87 restless legs when lying in bed.85 feeling tension in the legs.84 disturbed sleep by restless legs.82 strange tingling and itching feelings in the legs.77 leg muscle cramp when lying in bed.71 an urge to move the legs before sleeping.60 muscular pain in legs at awakening.53 trampling a lot at night.49 tired legs in the morning Factor 4 Apnea syndrome 4.0%.87 snoring loudly and bothering others.86 snoring when sleeping.74 snoring worsens if sleeping on back.71 stop breathing in sleep.66 sleep disturbs partner s sleep.60 body mass index.59 snoring worsens after drinking alcohol.41 awake suddenly gasping for breath Factor 5 Hypersomnia 3.4%.81 struggling to stay awake in the daytime.76 feeling sleepy at fixed intervals in the daytime.71 falling asleep accidentally.58 trouble doing my job as a result of sleepiness.55 traffic accidents as a result of sleepiness.44 daytime napping Factor 6 Daytime disfunctioning 2.7%.64 looking up to the day in the morning.58 being moody because of too little sleep.57 disfunctioning during the day.53 not enjoying things.47 trouble doing my job as a result of sleepiness.42 dissatisfied with job.41 getting easily tired 119

4 Factor 7 Hypnagogic hallucinations/dreaming 2.4%.74 hallucinations after awakening.71 hallucinations before or after a nap.67 having many vivid dreams.57 vivid dreams during daytime naps.55 unpleasant dreams Factor 8 Sexual and social dissatisfaction 2.0%.80 dissatisfied with sexual life.73 unhappy about loving relationships.54 unhappy about social life.41 decreased desire for sex Factor 9 Sleep paralysis 2.0%.69 paralyzed after a nap.67 paralyzed after awakening.50 paralyzed feeling when falling asleep.49 tired legs in the morning Factor 10 Cataplexy 2.0%.76 weak knees when laughing.73 sudden muscular weakness.45 fear of going outside Factor 11 Restless sleep 1.8%.73 making a mess of the bed-clothes.65 tossing and turning in bed.54 restless sleep.53 trampling a lot at night Factor 12 Negative conditioning 1.6%.56 feeling suddenly awake when going to bed.51 becoming angry when not falling asleep quickly Factor 13 Automatic behavior 1.5%.59 doing things which make no sense.54 impaired memory.54 acting without remembering.43 difficulties to concentrate 120

5 Table 2: Internal consistencies (Cronbach s alfa) Factor Alfa Insomnia 0.93 Psychiatry 0.92 Restless legs 0.90 Apnea syndrome.88 Hypersomnia 0.81 Daytime disfunctioning 0.80 Hypnagogic hallucinations/dreaming 0.76 Sexual and social dissatisfaction 0.73 Sleep paralysis 0.70 Cataplexy 0.64 Restless sleep 0.74 Negative conditioning 0.49 Automatic behavior 0.69 DISCUSSION The factors represent the most common areas of sleep disorders (insomnia, psychiatric sleep disorder, periodic movement of the limb syndrome, sleep apnea syndrome, hypersomnia) and sleep related problems (daytime disfunctioning, hypnagogic hallucinations, sexual and social dissatisfaction, sleep paralysis, cataplexy, restless sleep, negative conditioning and automatic behavior). Cronbach s alpha for the sleep disorder factors ranged from 0.93 to 0.81, indicating a high degree of internal consistency. It can be concluded that the Sleep Diagnosis List screens for general sleep disorders. REFERENCES 1. Douglass AB, Bornstein R, Nino-Murcia G, Keenan S, Miles L, Zarcone VP, Guilleminault C, Dement WC (1994). The Sleep Disorders Questionnaire I: creation and multivariate structure of SDQ. Sleep 17: Sweere Y, Kerkhof GA, De Weerd AW, Kamphuisen HAC, Kemp B, & Schimsheimer RJ (1998). The validity of the Dutch Sleep Disorders Questionnaire (SDQ). Journal of Psychosomatic Research (In press). 121