Investigating couples' sleep: an evaluation of actigraphic analysis techniques.

'Blip' analysis, fast wavelet transformations (FWT) and correlation analysis have all been used to actigraphically assess the impact one person is having on another's sleep, yet no review exists as to the differences between, and applicability of, these methods for investigating couples' sleep. Using actigraphy data and audio sleep diaries collected from 18 couples, this paper provides such a review. This paper constructs and assesses two novel, analytical methods: Lotjonen's sleep/wake algorithm, and the partner impact on sleep wake analysis (PISWA). Both 'blip' analysis and correlation suggest that the strongest relationship between bed partners occurs on an epoch-to-epoch basis. However, 'blips' deal strictly with onset of movement and fail to incorporate strength and duration of movement. Conversely, correlation analysis incorporates some elements of strength and duration of movement but makes identification of onset problematic. FWT offer useful 'relativistic' pattern recognition, identifying onset, strength and duration of movement, but are difficult to quantify. Although audio diary data support the potential of Lotjonen's sleep/wake algorithm to identify sleep non-movement, sleep movement, wake non-movement (or quiet wakefulness) and wake movement, the problem remains that this method also relies on visualization. Of most promise, we argue, is the PISWA, which examines 'impact' of bed partners through incorporating elements of 'blip' analysis and the sleep/wake algorithm.