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Table 1 Comparison of snapshot and constant-age tracking trends in IDEA autism prevalence for 7 to 10-year intervals beginning in birth years 1988 (interval 1) and 1993 (interval 2)

From: A comparison of temporal trends in United States autism prevalence to trends in suspected environmental factors

Interval 1 (snapshot based on 2005 report)

Interval 2 (snapshot based on 2010 report)

  

b snap

b track

b snap b track %

Birth

N

b snap

b track

b snap b track %

Birth

N

Track

Min.

10 -4 y -1

10 -4 y -1

 

Year

 

10 -4 y -1

10 -4 y -1

 

Year

 

Age

Snap

 

Span

 

Span

 

Age

4.1 ± 1.5

5.3 ± 2.1

78 ± 8

1988-1997

24

6.3 ± 2.1

8.6 ± 2.6

73 ± 8

1993-2002

19

8

8

4.4

5.4

82

 

1

6.8

8.7

78

 

1

 

4.2 ± 1.6

5.6 ± 2.2

77 ± 8

1988-1996

22

6.2 ± 2.2

8.5 ± 2.7

73 ± 8

1993-2001

22

9

9

4.5

5.5

81

 

1

6.9

8.7

80

 

1

 

4.6 ± 1.6

6.0 ± 2.2

78 ± 7

1988-1995

21

6.6 ± 2.3

9.0 ± 2.9

74 ± 8

1993-2000

18

10

10

4.7

5.7

81

 

1

7.0

8.8

80

 

1

 

5.2 ± 1.8

6.7 ± 2.4

77 ± 8

1988-1994

17

7.5 ± 2.9

9.8 ± 3.4

76 ± 8

1993-1999

11

11

11

4.8

6.0

81

 

1

7.0

8.6

81

 

1

 
  1. Snapshot slopes for interval 1 and 2 are based on the 2005 and 2010 IDEA reports, respectively. Slopes (symbol b, in units of # 10-4 y-1) are estimated based on least squares linear regression. The bottom line (N = 1) in each age pair shows results for California. The top line shows the mean and standard deviation for all states (N = 11 to 24) for which the error in the constant-age tracking slope is < 10% and the error in the snapshot slope is < 15%. The snapshot:tracking slope ratio is reported as a quantitative estimate of the fraction (in%) of the constant-age tracking slope that is "real" rather than due to better and expanding diagnosis. A range of tracking ages from 8 to 11 is considered.