**Conflict of interest**

*Psychopathology - An International and Interdisciplinary Perspective*

interval for a true effect.

Our meta-analysis did not provide a clear conclusion either, but allowed us to contribute to the knowledge in this area by statistically synthesizing the data, taking into consideration the relative weight of each study, and providing a confidence

should emphasize precision in reports of subjective sleep complaints.

The absence of standards in NPA reporting complicated study comparison, with the result that many studies were excluded from our estimates. Moreover, few authors specified whether or not apprehensiveness about possible future NPA was present. As discussed previously, the presence of apprehensiveness is important because it is hypothesized to increase arousal and maintain insomnia. In the absence of apprehensiveness, interactions between NPA, insomnia, and PD are less clear. We therefore suggest the use of standardized frequency criteria for NPA prevalence that include apprehensiveness about future NPA. The criterion used by Craske et al. [59] and Albert et al. [60] constitutes a good example. The use of a standardized measure of NPA (e.g., the appendix to ADIS-IV for NPA) would contribute to the generation of standardized data. This section of the ADIS-IV is clinician-administered; developing a self-report version could also make standardized evaluation of NPA more accessible. However, since ADIS-IV has been updated to ADIS-5, an update of the appendix to DSM-5 criteria is needed before any other developments

In conclusion, this systematic literature review confirms the presence of both subjective and objective insomnia in patients with PD. The results indicate that sporadic NPA are common in this population, i.e., more than one in every two patients with PD (52.1%) report at least one lifetime NPA. Recurrent NPA with apprehensiveness about future episodes seems to be slightly less common (40.9%) and is hypothesized to trigger and maintain insomnia. However the reliability of

We would like to emphasize the importance of using standardized psychometric tools such as the PSQI when reporting research data about sleep in patients with PD. Moreover, reporting results for subscales could give a better and more complete idea of the type of sleep alterations patients are experiencing. Also, research in this area would benefit from greater standardization in reports of subjective sleep and NP, and from particular attention in detailing subscales and information about diverse sleep variables (e.g., sleep latency, sleep efficiency,

this last prevalence is low and needs confirming in future research.

A significant number of studies with subjective sleep data could not be used because they used diverse self-report questionnaires. For example, a study by Batterham et al. in 2012 [48] was the only one to use the Goldberg depression and anxiety scale questions about sleep. While some of the data could have been merged into a single analysis designed to answer the question "Is there a significant difference in subjective sleep between patients with PD and healthy controls?", such an analysis would not have provided information about specific sleep disturbances. The majority of studies using PSQI did not report scores for the seven subscales. The inclusion of this data would have permitted a better comparison of subjective and objective sleep data. Previous research indicates that there is a misperception of sleep in some subjects with insomnia, who overestimate sleep onset latency and underestimate total sleep time [57, 58]. Conversely, other subjects tend to overestimate their total sleep time [58]. It would have been interesting to compare the results of the meta-analysis for subjective and objective sleep data. Future research

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awakenings, etc.).

take place.

**5. Conclusion**

The authors have no conflict of interest to declare.
