Table 1

Spacing of peak expiratory flow (PEF) readings when fewer than 10 were used

No. of PEF readings used	Spacing of PEF readings used	Mean difference in diurnal variation	Limits of agreement of diurnal variation
2	wake 1, 10 bed	−2.80	1.57 to −12.3
3	wake 1, 6, 10 bed	−1.72	1.86 to −5.53
4	wake 1, 3, 7, 10 bed	−1.30	1.57 to −2.66
5	wake 1, 3, 5, 8, 10 bed	−1.20	1.54 to −2.21
6	wake 1, 3, 4, 5, 8, 10 bed	−1.14	1.46 to −1.91
7	wake 1, 3, 4, 5, 7, 8, 10 bed	−1.08	1.32 to −1.53
8	wake 1, 3, 4, 5, 6, 7, 8, 10 bed	−1.06	1.28 to −1.43
9	wake 1, 2, 3, 4, 5, 6, 7, 8, 10 bed	−1.02	1.14 to −1.18

PEF readings were performed two hourly over waking hours. Reading 1 represents the reading taken on waking, reading 10 represents the reading taken on retiring to bed, and readings 2–9 represent those readings performed at approximately two hourly intervals throughout the day. Mean underestimates of true diurnal variation and limits of possible underestimates of diurnal variation are also shown.