A review of evidence for the claim that children are sleeping less than in the past

Abstract

Study objectives: The notion that children are sleeping less than they used to is widespread. This study examined the strength of the evidence for this idea by tracing a "scholarly genealogy" of the claims presented within the literature.

Design: A systematic review of peer-reviewed literature was conducted to identify claims of a secular trend in children's sleep. For each identified claim, the references cited were reviewed.

Measurements and results: The review identified 51 studies. Of these, 17 evinced evidence (2 reported increases, 3 reported no change, 6 reported mixed trends, 6 reported decreases) and 34 provided statements without evidence. Although the evidence that sleep duration has declined is contested, all 34 studies reported a decline. Examination of the references cited revealed that 17 papers referred directly to studies which provided evidence, 4 papers referred indirectly to studies which provided evidence, 9 papers did not provide any evidence and 4 papers referred to studies which could not be located. Of the papers that did provide evidence, 85% referred to one of 3 sources of evidence, each of which was of moderate quality.

Conclusions: The genealogy of the notion of secular declines in children's sleep reveals a limited scientific basis. The apparent evidence base is inflated by repeated references to the same sources of evidence, reference to secondary sources, mis-referencing, and a failure to cite contrary evidence.

Keywords: Sleep; adolescents; bias; children; trends.

Figure 1

Secular trends in children's sleep as reported within the literature. The graph above illustrates findings of 15 of the 17 studies identified for selected ages. The results of two studies are not illustrated as sleep duration values were not explicitly reported or did not report the sleep times for children in the age groups graphed. *Zuzanek examined secular trends in children sleep from 7 different countries. While the years of measurement and average sleep duration were specified for Finland, Germany, Canada, and Norway, they were not specified for Australia, France, and the USA, all of which were identified as showing increases. For this reason, only trends for Finland, Germany, Canada, and Norway have been included in the graph above.

Figure 2

Location of evidence of a secular trend in children's sleep duration according to study's results and times cited. The location of the evidence, that is, where the study is actually available was determined by assessing the source of publication and by searching Google. Whether an article appeared in Google was determined by typing the title of the article in single quotation marks. Citation frequency was calculated through the use of Google Scholar. Study reference: 26 Dollman, 27 Iglowstein, 28 Kohyama, 29 Thorleifsdottir, 30 Hofferth, 31 Huysmans, 32 Pääkönen, 33 Randler, 40 Soupourmas, 41 Weissbluth, 42 Knutson, 43 Vaage, 44 Zuzanek, 45 Statistics Bureau, 46 Webb, 47 Tynjälä (2002), 75 Tynjälä (2010).

Figure 3

Scholarly genealogy of claims within the literature.