Original ArticlePrevalence of insomnia and sleep characteristics in the general population of Spain☆
Introduction
Several studies on the epidemiology of insomnia in North America and various European countries have been published in the last decade [1], [2], [3], [4], [5], [6], [7], [8], [9], [10]. Most of these studies were limited to the analysis of insomnia symptoms [2], [3], [6], [7], [8]. These symptoms were assessed mainly using three kinds of answer choices to insomnia questions. In the first studies, the participants had to report if they experienced insomnia symptoms using binary answers (for example, yes/no or present/absent choices) [2], [3]. Other studies graded the answer choices on intensity scales (for example, not at all to greatly bothered by the symptom) or on frequency scales (for example, never, sometimes, often, or on frequency/week) [6], [7], [10]. These methodological diversities brought important variations in the prevalence of insomnia symptomatology from one study to another, therefore rendering hazardous the comparisons between these studies.
Most of the studies, after presenting the prevalence for each symptom, group together all the symptoms under the label insomnia. Unfortunately, few studies have assessed other sleep dimensions that could be related to each insomnia symptom. For example, epidemiological studies usually assessed the prevalence of difficulty initiating sleep with a single question to which the participants answered using a frequency or severity scale. However, most studies did not cross this information with other results such as the reported sleep latency. As a consequence, there is little information about how insomnia symptoms relate to other sleep parameters that could ascertain the presence of an insomnia symptom or, at least, better define it [11]. Better ways to assess symptoms in epidemiology are necessary to increase the precision in the symptom definition. Epidemiological studies examining the impact of insomnia symptoms on daytime functioning have shown that only about half of individuals reporting insomnia symptoms three nights/week or more also experience daytime impairment [12].
In this report, the epidemiology of insomnia symptoms and diagnoses was studied in a representative sample of 4065 individuals of the Spanish population. Each insomnia symptom was examined in relationship to other parameters related to sleep quality and sleep quantity.
Section snippets
Sampling
A representative sample of the Spanish population was interviewed between December 1998 and April 1999 under the supervision of the principal investigator (M.M.O.). The study aimed to document sleep habits, and sleep and mental disorder diagnoses in the Spanish general population. The targeted population consisted of non-institutionalized inhabitants 15 years of age and older living in Spain (including the Canary Islands). This represented 38.5 million inhabitants. The sample was drawn according
Description of the sample
Participants were aged between 15 and 96 years (Table 1). Women represented 51.5% of the sample. Half of the participants were married and one-third were single. Working participants represented 45% of the sample. Ten percent of the sample had little or no education and nearly one-third went to school 9 years or less.
Symptomatology
Among the participants, 3.7% (95% C.I. 3.1–4.2%) reported having difficulty initiating sleep at least three evenings/week. This prevalence was comparable among age groups (Fig. 1)
Discussion
This study was performed in Spain, which previously had been little studied in sleep epidemiology. The target population consisted of 38.8 million inhabitants aged 15 years or older. The Canary Islands were also included in the sampling and accounted for 4.3% of the participants.
Some limitations of this study need to be underlined. The question of the reliability of sleep data collected by telephone could be mentioned. Telephone surveys are used more and more in epidemiologic research and in
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This study was supported by an unrestricted educational grant from Sanofi to the Principal Investigator (M.M.O.).