Introduction.

Diverse studies llave demonstrated the relationship between psychopathology and sleep alterations. Data proceeding from the ambulatory psychiatric field show that 70-75% of the patients experience sleep problems. The most frequent complaints refer to nighttime sleep alterations, excessive daytime sleep, difficulty with morning waking, and disturbances in the circadian rhythm of the sleep-wake cycle. Many studies, most of which use patient samples, have associated psychopathological personality traits and sleep disorders. All of these studies reveal that subjects with sleep disorder tend to be characterized by psychopathological traits (anxiety, psychasthenia, depression, etc.). There is some evidence that the structure of some dream dysfunctions (such as insomnia) is similar among general population and psychiatric samples; differences are more quantitative than qualitative. In samples of university students, the percentage of individuals who report bad sleep quality has been similar to the percentage of insomniacs in general population. With the aim to delve more deeply into the analogy between the sleep quality of normal subjects and clinical samples, and given the shortage of studies relating psychopathological traits of personality and sleep quality in normal population, this study intends to explore the relationship between the psychopathological personality variables included in the Minnesota Multiphasic Personality Inventory-2 (MMPI-2) and the sleep quality evaluated with the Pittsburg Sleep Quality Index in a sample ofsubjects who have no diagnosed sleep disorder. The psychopathological variables included in the MMPI-2 which predict sleep quality in a non-clinical sample are also determined.

Methodology.

A sample of 222 individuals (186 women and 36 men) with a mean age of 21.65 years (SD=2.81) completes the Minnesota Multiphasic Personality Inventory-2 (MMPI-2) and the Pittsburg Sleep Quality Index (PSQI), which provide an overall sleep quality measure and seven partial scores for different dimensions: Subjective sleep quality, Sleep latency, Sleep duration, Sleep habit efficiency, Sleep alterations, the use of hypnotic medication, and daytime dysfunction.

Results.

Some psychopathological traits (hypochondria, anxiety, and depression) correlate positively with almost all of the sleep quality dimensions comprising the PSQI. From a logistic regression model developed to predict the probability of being a good or bad sleeper, hypochondria and anxiety are the only statistically significant predictors.

Discussion and conclusions.

Human sleep, from a behavioral perspective, would be explained from four different dimensions: Circadian time (sleep-wake cycle situation on the nictemero), Organism (intrinsic factors such as age, sleep patterns, emotional states, etc.), Behavior (facilitating or inhibiting behaviors), and Environment (temperature, light, noise, etc.). Psychopathological personality traits, the main objective of this study, can also be included within the second component (organism). Previous studies using the MMPI have associated insomnia to high anxiety levels, depression, hypochondria, hysteria, and psychasthenia. The MMPI has also been considered to be a useful instrument in identifying different personality profiles ininsomnia subjects. There are, however, only a few studies focusing on the relationship between these personality traits and sleep quality in normal subjects. The results indicate that this study sample the subjects do not present serious sleep disorders. All of the components pertaining to the Pittsburg Sleep Quality Index present mean scores below the middle response range, situated in 1.5. However, if we consider the total score and bear in mind that a score of five is the cut-off point used to differentiate good sleepers from bad sleepers, we can classify 45.94% of the sample as bad sleepers. In considering the scores for the different MMPI-2 clinical scales, we should mention that none of them reached the typical score of 60; therefore no trait was found to be clinically significant. Some psychopathological traits are linked to almost all of the sleep quality dimensions. Hypochondria, anxiety, and depression are present in the associations with subjective sleep quality, disturbances, or daytime sleepiness. Though no stronger relations between use of hypnotic medication and psychopathological traits have been found (none of them above 0.30), a similar trend on patients dependent on benzodiazepines (predominating traits as depression, psychasthenia and schizophrenia) has been showed. It is also important to point out the relationship between daily dysfunction and the WRK scale (work interferences), which reveals the negative effects of daytime sleepiness, even in subjects who do not present important sleep disorders, as in this sample. On the other hand, the relationship between daily dysfunction and hypochondria, depression, and schizophrenia found in this study has previously been verified in patients with excessive daytime sleepiness. When considering the global score, we can clearly inform that health concerns (reflected in the Hs, HEA, and Hy scales) and the negative emotional states (D, ANX, and DEP scales) are related to sleep quality. These two factors (health concerns and anxiety) are part of the regression model, revealing that an increase in hypochondria and anxiety scores significantly increases the probability of being a bad sleeper, that is to say, of having a poor sleep quality. This explicative model presents a good predictive capacity which allows us to correctly classify 68.50% of the sample. We can correctly predict 78.30% of the good sleepers and 53.90% ofthe bad sleepers (scores higher than 5 on the Pittsburg global index), which grants the model an adequate specificity and sensibility. It is, however, necessary to consider that data used for the estimation respond to a range of restricted scores, causing any effect to be much less important than if we had worked with a more heterogeneous group of subjects. For example, global sleep quality scores can oscillate between 0 and 21, but in our sample they are comprised between 0 and 15. It is possible that, in including subjects who present high scores on the scales used in this study, a greater number of significant sleep quality predictors with greater magnitudes would be emphasized. Nevertheless, our interest resides in exploring the relationship between health concerns, anxiety and depression levels, and sleep quality in a non-clinical sample. So far, this relationship has not been explored in depth. One common limitation of these non-randomized studies is the difficulty to generalize findings to the normal population. Nevertheless, we assume higher possibilities to generalize findings if our study results are similar to those obtained from other non-clinical samples. In conclusion, health concerns and anxiety levels are the psychopathological traits most related to sleep quality and which hold a certain capacity to determine this quality in a sample of normal subjects. Both variables are clearly related to insomnia, as has been revealed in many insomnia patient studies. Therefore, we can verify that the pattern followed in the relationship between psychopathological traits and sleep quality in a non-clinical sample is similar to that found in sleep disorder patient samples, supporting that relationship between psychopathological traits and sleep quality in normal subjects opposite to patients with dream disorders can be drawn more easily from a quantitative than a qualitative approach.

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