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Table 3 Bias [90% prediction intervals] of variance component estimates for percentage time above 90° for a subset of the investigated sampling strategies

From: Accuracy and precision of variance components in occupational posture recordings: a simulation study of different data collection strategies

n s

10

10

10

10

20

20

20

20

ttot

120

120

480

480

120

120

480

480

nd

2

4

2

4

2

4

2

4

3a. Between-subjects variance, σ 2 BS

t b

1

r

0.0

−0.2

−0.1

−0.1

−0.1

−0.1

−0.2

−0.2

[−3.0, 5.3]

[−3.0, 4.1]

[−3.0, 4.1]

[−2.8, 3.0]

[−3.0, 3.6]

[−2.6, 2.7]

[−2.9, 2.7]

[−2.0, 1.9]

 

1

f

0.0

−0.1

0.0

−0.3

−0.1

−0.2

0.0

−0.3

[−3.0, 5.0]

[−3.0, 3.8]

[−3.0, 4.2]

[−2.9, 2.5]

[−3.0, 3.4]

[−2.4, 2.5]

[−2.7, 2.7]

[−2.1, 1.7]

 

15

r

0.8

0.4

−0.1

−0.2

0.2

0.0

−0.2

−0.2

[−3.0, 11.1]

[−3.0, 9.7]

[−3.0, 4.8]

[−3.0, 4.1]

[−3.0, 7.6]

[−3.0, 6.3]

[−3.0, 3.1]

[−2.6, 2.6]

 

15

f

0.5

0.3

−0.5

−0.6

0.1

0.0

−0.6

−0.7

[−3.0, 9.9]

[−3.0, 9.4]

[−3.0, 3.3]

[−3.0, 2.8]

[−3.0, 6.6]

[−3.0, 6.2]

[−3.0, 2.1]

[−2.8, 1.6]

 

60

r

1.6

 

0.0

−0.1

0.7

 

−0.2

−0.2

[−3.0, 17.3]

 

[−3.0, 5.8]

[−3.0, 5.5]

[−3.0, 11.5]

 

[−3.0, 3.7]

[−3.0, 3.6]

 

60

f

  

−0.3

0.1

  

−0.4

−0.1

[−3.0, 5.0]

[−3.0, 5.7]

  

[−3.0, 3.2]

[−3.0, 3.6]

3b. Between-days variance, σ 2 BD

t b

1

r

−0.2

−0.1

−0.1

0.0

0.0

0.0

0.0

0.0

[−4.0, 6.1]

[−4.0, 5.3]

[−3.4, 4.8]

[−2.5, 3.2]

[−3.5, 4.6]

[−3.3, 3.8]

[−2.6, 3.3]

[−1.9, 2.3]

 

1

f

−0.8

−1.1

−0.3

−0.3

−0.7

−1.1

−0.2

−0.3

[−4.0, 5.3]

[−4.0, 3.7]

[−3.4, 4.7]

[−2.8, 2.9]

[−4.0, 3.6]

[−4.0, 2.4]

[−2.8, 3.4]

[−2.2, 1.9]

 

15

r

8.2

20.2

0.9

3.5

8.7

20.3

1.0

3.6

[−1.8, 24.5]

[4.0, 44.6]

[−3.0, 6.7]

[−0.7, 9.0]

[0.5, 20.5]

[7.5, 37.5]

[−2.1, 5.1]

[0.5, 7.5]

 

15

f

7.1

19.2

0.1

2.6

7.3

19.4

0.3

2.7

[−1.9, 20.9]

[3.9, 41.9]

[−3.3, 5.0]

[−1.0, 7.4]

[0.1, 16.9]

[7.4, 35.1]

[−2.6, 4.0]

[−0.1, 6.2]

 

60

r

17.2

 

2.0

7.3

17.6

 

2.1

7.4

[−0.5, 51.0]

 

[−2.7, 9.0]

[0.7, 17.0]

[2.7, 42.0]

 

[−1.6, 7.2]

[2.4, 14]

 

60

f

  

1.3

7.7

  

1.5

7.9

[−2.8, 7.2]

[1.0, 17.9]

  

[−1.8, 6.0]

[2.6, 14.7]

3c. Within-day variance, σ 2 WD

t b

1

r

0.1

−0.1

−0.9

0.2

0.5

0.2

−0.3

−0.1

[−50.5, 54.8]

[−46.7, 50.8]

[−42.9, 42.3]

[−37.3, 38.9]

[−35.6, 39.1]

[−33.1, 34.9]

[−29.8, 31.4]

[−27.2, 27.1]

 

1

f

0.5

−0.2

1.1

0.5

0.6

0.4

1.4

0.3

[−48.9, 54.1]

[−44.3, 47.7]

[−42.0, 46.5]

[−35.9, 38.4]

[−34.3, 37.3]

[−32.2, 33.4]

[−29.9, 33.6]

[−26.2, 25.9]

 

15

r

−8.8

−19.0

0.7

−2.1

−6.9

−18.7

0.6

−1.9

[−72.9, 61.4]

[−74.3, 43.3]

[−43.7, 47.3]

[−44.3, 42.9]

[−53.8, 43.5]

[−60.0, 26.1]

[−31.6, 34.4]

[−31.5, 29.5]

 

15

f

−8.5

−16.7

−2.4

−6.2

−9.2

−17.6

−1.5

−5.9

[−70.0, 60.7]

[−73.8, 46.3]

[−44.4, 43.5]

[−44.6, 35.2]

[−55.3, 39.9]

[−59.3, 26.5]

[−31.0, 29.2]

[−33.8, 23.6]

 

60

r

−13.0

 

1.2

−3.2

−13.3

 

1.0

−2.7

[−80.6, 65.7]

 

[−45.6, 53.2]

[−47.5, 45.8]

[−61.0, 39.5]

 

[−34.0, 36.9]

[−34.9, 32.5]

 

60

f

  

−1.1

3.1

  

−0.5

4.1

[−47.2, 47.9]

[−42.1, 52.8]

  

[−32.0, 34.0]

[−29.0, 39.7]

  1. a, b, c: between-subjects, between-days, and within-day variance.
  2. n s , number of subjects; t tot , total sampling time per subject (minutes); n d , number of days per subject; t b , size of sampling blocks (minutes); r, random sampling; f, fixed interval sampling.
  3. Bias and prediction intervals are presented relative to the “true” variance components of the parent data set, i.e. σ 2 BS  = 3.0, σ 2 BD  = 4.0 and σ 2 WD  = 164.7 (cf. Table 2). Thus, the result in bold and italics tells that for the sampling strategy (n s , t tot , n d , t b ) = (10, 120, 4, 1) with random distribution of blocks, σ 2 BS was downward biased by 0.2, i.e. its average estimated value was 2.8, and the 90% prediction interval, presented as [−3.0, 4.1], reached from 3.0-3.0 to 3.0 + 4.1, i.e. from 0.0 to 7.1.
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BMC Medical Research Methodology

ISSN: 1471-2288

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