Insomnia Definitions

First created | 05/12/2002

Last edited | 05/11/2012

Summary by Maurice M. Ohayon, MD, DSc, PhD

Reference to cite: Ohayon MM. Epidemiology of insomnia: what we know and what we still need to learn. Sleep Med Rev. 2002 Apr;6(2):97-111

More than fifty studies of insomnia based on data collected in various representative community-dwelling samples or populations were published with highly variable rates

These surveys provide estimates of the prevalence of insomnia according to four definitions:
     - insomnia as a symptom,
     - insomnia as a symptom with daytime consequences,
     - insomnia as a Global Sleep Dissatisfaction (GSD, Ohayon 1993),
     - insomnia as a diagnosis (according to the psychiatric classification or the one of the sleep specialists).

The first definition

The first definition is based on insomnia as a simple criteria. Four major criteria are commonly used:
     - Difficulty Initiating Sleep,
     - Difficulty Maintaining Sleep,
     - Early Morning Awakening,
     - Non Restorative Sleep.

Many epidemiological used one of these 4 criteria to qualify a subject to be insomniac.

Early Morning Awakening is a troublesome symptom: how to define "early" in the general population?

According to this classical way, we found in our studies that about one-third of the general population presents at least one of them.

These results are giving an inflating point of view of insomnia in the general population.

The second definition

The second definition is taking into account the fact that a subject with one the 4 previous criteria must have also daytime consequences before to be considered insomniac.

According to this way to define insomnia, many researchers found a prevalence of insomnia between 9% and 15% in the general population.

These results are much lower than those corresponding to the first definition.

The third definition

The third definition is based on the Global Sleep Dissatisfaction (GSD, Ohayon 1993).

The idea is based on the paradigm that "insomnia is first defined by the subject himself, by his persistent complaint (at least 6 months) about the quality or the quantity of his sleep" (Ohayon, 1994).

According to this definition, several studies found a prevalence of 8-18% of the general population.

This prevalence is close to the one found for the second definition.

However, the subjects of the second and third definition have not the same characteristics.

The fourth definition

This last definition gives to the concept of insomnia a status of disease: insomnia is defined as a complete entity including a set of criteria and different conditions.

Primary and secondary insomnia are distinguished.
The psychiatric and sleep classifications define different sets of diagnoses.
A Differential Diagnostic Procedure must be applied in order to validate the positive diagnosis. This procedure is an elimination procedure aiming to explore all concurrent diagnoses.

Using this decision-making process including a differential diagnosis, we found that the prevalence of insomnia as a diagnosis (according to the DSM-IV classification) is 6%.

A part of the population with GSD is not reaching a diagnosis.
This means that a part of the subjects complaining about their sleep cannot find a place in the Insomnia Diagnosis Category of the DSM-IV.

Moreover, another part of the population does not present any criteria of insomnia as defined by the DSM-IV or the ICSD.

Conclusions

These four definitions of insomnia have higher prevalence rates in women than in men.

However, this difference is disappearing when using a criterion of duration: chronic insomnia (for at least 6 months) is not gender related.

It is why GSD with its definition including a duration of 6 months is not changing with gender while the other definitions are doing it.

The prevalence of insomnia symptoms generally increases with age, while the rates of Global Sleep Dissatisfaction and Insomnia Diagnoses have little variation with age.

Moreover, GSD and Insomnia Diagnoses have a discrepancy of 1 to 5%.

We showed that DSM-IV classification is not taking into account a certain class of people presenting GSD, but not the 4 insomnia symptoms.

Again, we must stress that someone may have one or several insomnia symptoms and still be happy with his sleep!

On the contrary, GSD is pointing directly on the pathological cases.

Future epidemiological studies should focus on the natural evolution of insomnia.

Epidemiological genetic links of insomnia are yet to be studied.

Reference

Content of thispage is extracted from:

Ohayon MM. Epidemiology of insomnia: what we know and what we still need to learn. Sleep Med Rev. 2002 Apr;6(2):97-111.

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