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ASSESSMENT OF TOTAL SLEEP TIME BY ACTIGRAPHY: INTRA-INDIVIDUAL VARIABILITY AND MEASUREMENT RELIABILITY. Lilian de Jonge , Martin Requena and Giovanni Cizza for the Sleep Extension Study Group

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ASSESSMENT OF TOTAL SLEEP TIME BY ACTIGRAPHY: INTRA-INDIVIDUAL VARIABILITY AND MEASUREMENT RELIABILITY.

Lilian de Jonge, Martin Requena and Giovanni Cizza for the Sleep Extension Study Group

Section on Neuroendocrinology of Obesity, Diabetes, Endocrinology and Obesity Branch, NIDDK/NIH, Bethesda MD, USA

ABSTRACT

Objective:The objective of this study was to determine the intra-individual variability and measurement reliability of the assessment of total sleep time by actigraphy.

Methods: Screening data of 126 obese, sleep deprived individuals, who were randomized for the Sleep Extension Study, a randomized, controlled, prospective study of obese, sleep-deprived men and premenopausal women, aged 18-50 between January 2007 and March 2011, were included in the analysis. Total sleep time was assessed by wrist actigraphy (Actiwatch-64, Respironics/Philips, Bend OR) for 14 consecutive days. Variability of the measurement was expressed as coefficient of variation (CV) and the reliability was calculated as

ê= between subjects mean square- within subjects mean square

within subjects mean square

_kê__

Measurements reliability estimate (RE) = 1 + kê

Measurements were considered acceptable when RE >0.80

Results: Average within individual CV was 19.3% while the between individual CV was 32%. RE ranged from 0.83 for a single day measurement and 0.99 for 14 days of measurement. RE was not significantly different from 14 days of measurements with at least 4 days of measurement (p<0.05).

Discussion:The results of this study suggest that, although an acceptable measurement reliability can be obtained with a single day of actigraphy, at least 4 days are necessary to obtain a measurement reliability comparable to 14 days in our study population.

Results

METHODS

STUDY COHORT

126 participants (96F/30M) were randomized for the Sleep Extension Study between january 2007 and July 2011. The Sleep Extension Study is a randomized, prospective, intervention trial of obese (BMI 29-55 kg/m2) men and premenopausal women aged 18 to 50 years old who report sleeping less than 6.5 hours per night on average.

ANTHROPOMETRICS

Body composition was measured in Body Mass Index (BMI), waist and neck circumference, DEXA and CT scans.

SLEEP MEASUREMENTS

Wrist actigraphy (Phillips Respironics, USA) objectively measured sleep duration andsleep efficiency over two weeks. Subjective sleep duration was a part of the Pittsburgh Sleep Quality Index (PSQI). Sleep quality was evaluated by the PSQI global score, Epworth Sleepiness Scale, and Respiratory Disturbance Index score as measured with an ARES unicorder. (Watermark Medical, USA).

STATISTICS

Variability of the of the measurement was expressed as coefficient of variation (CV) and the reliability was calculated as

ê= between subjects mean square- within subjects mean square

within subjects mean square

_kê__

Measurements reliability estimate (RE) = 1 + kê

Measurements were considered acceptable when RE >0.80

  • RESULTS
  • Average within individual CV was 19.3% while the between individual CV was 32%.
  • RE ranged from 0.83 for a single day measurement and 0.99 for 14 days of measurement. RE was not significantly different from 14 days of measurements with at least 4 days of measurement (p<0.05).
  • CONCLUSIONS
  • The results of our study suggest that:
  • although an acceptable measurement reliability can be obtained with a single day of actigraphy, at least 4 days are necessary to obtain a measurement reliability comparable to 14 days in our study population.