Sleepiness is certainly associated with such sleep disorders as sleep apnea and narcolepsy, but it is also a phenomenon that ‘intrudes’ into the waking state of ‘healthy sleepers’, who may or may not have experienced some loss to their normal daily quota of sleep in the preceding night(s). There is strong evidence that there is a high incidence of road accidents where sleepiness is the most likely cause (Horne & Reyner, 1995; Lyznicki et al., 1998), and, more broadly, that sleepiness has an important impact on general health (Dement & Mitler, 1993; Briones et al., 1996). There is however discordance over what exactly sleepiness is and how to measure it (Johns, 1998). These are issues of utmost importance. Clearly, to be able to successfully manage sleepiness, we need to have a sophisticated understanding of the phenomenon, and to do so, we need effective measurement tools.
This essay will constitute a critique of the measurement of sleepiness. However the author will not take the usual approach of looking at the individual measurement tools (i.e. methods) used by researchers in this endeavour and their relative strengths and weaknesses. Instead, it is proposed that a richer critique might be achieved through viewing the measurement of sleepiness as encompassing both; 1) the methods the researcher chooses to examine this phenomenon; and 2) the researcher’s interpretation of the results.
The underlying assumption made by adopting this approach is that measurement can be seen to be multi-dimensional, consisting of the tool(s) used by the researcher and the practice in which the researcher engages when interpreting the results obtained. Theorising as to how these two aspects of research interact should form the basis for some interesting discussion. The multiple sleep latency test (MSLT) will be focused on in a little bit more depth than the other tools as the author believes the MSLT not only provides a good basis for understanding sleepiness and its measurement, but will also allow us to look at the interplay between the two aforementioned dimensions of measurement. This essay will conclude by observing some present research endeavours pertaining to sleepiness and by contemplating what the future of the measurement of sleepiness might be.
Some Guidelines
Rather than attempt to define sleepiness thoroughly here at the start, the author will offer a simple working definition, more through necessity than volition. Until further elaboration ensues, ‘sleepiness’ is proposed to be simply ‘the phenomenon associated with a lack of sleep, as experienced during wakefulness, distinct to tiredness and fatigue’. The distinction between sleepiness and tiredness is an important one; they are taken to be qualitatively, as opposed to quantitatively different (see Horne, 2003). But this is just one aspect of the definition that deserves elaboration. Indeed, a second theme of this essay will be to elaborate on this definition once we have unravelled some of the complexities associated with the phenomenon of sleepiness. Before continuing, it is necessary to state that this essay will explore issues pertaining to human sleepiness. And furthermore, as experienced in young adults.
Overview of Sleep Function
Some of the discordance over what sleepiness is and how it should be measured is rooted in the wider, on-going debate over what exactly the function of sleep is. Approaching sleepiness from this perspective should thus be a useful starting point. However, an extensive discussion on this topic will be avoided, mainly because the parameters of this essay mandate such. Excellent summaries already exist on the different perspectives on sleep function (Rechtschaffen, 1998) and how they relate to the measurement of sleepiness (Horne, 1991). Providing a brief and crude overview of two different schools of thought will suffice.