Description

The distribution of body weight for young boys age 0-3 years can be used to evaluate the physical development of a child.

Data: body weight in kilograms

month

5th%

10th%

25th%

50th%

75th%

90th%

95th%

0

2.54

2.78

3

3.27

3.64

3.82

4.15

1

3.16

3.43

3.82

4.29

4.75

5.14

5.38

3

4.43

4.78

5.32

5.98

6.56

7.14

7.37

6

6.2

6.61

7.2

7.85

8.49

9.1

9.46

9

7.52

7.95

8.56

9.18

9.88

10.49

10.93

12

8.43

8.84

9.49

10.15

10.91

11.54

11.99

18

9.59

9.92

10.67

11.47

12.31

13.05

13.44

24

10.54

10.85

11.65

12.59

13.44

14.29

14.7

30

11.44

11.8

12.63

13.67

14.51

15.47

15.97

36

12.26

12.69

13.58

14.69

15.59

16.66

17.28

Polynomial equations approximating this data were calculated in JMP, as follows:

5th% for body weight in kilograms =

= ((-0.000006 * ((months)^4)) + (0.0007377 * ((months)^3)) - (0.033662 * ((months)^2)) + (0.8026072 * (months)) + 2.4385737)

10th% for body weight in kilograms =

= ((-0.000008 * ((months)^4)) + (0.0009205 * ((months)^3)) - (0.039229 * ((months)^2)) + (0.8609065 * (months)) + 2.666067)

25th% for body weight in kilograms =

= ((-0.000011 * ((months)^4)) + (0.0011489 * ((months)^3)) - (0.045737 * ((months)^2)) + (0.94444289 * (months)) + 2.9444435)

50th% for body weight in kilograms =

= ((-0.000016 * ((months)^4)) + (0.0015272 * ((months)^3)) - (0.054766 * ((months)^2)) + (1.036284 * (months)) + 3.2946854)

75th% for body weight in kilograms =

= ((-0.000016 * ((months)^4)) + (0.0015725 * ((months)^3)) - (0.057231 * ((months)^2)) + (1.0910312 * (months)) + 3.6915309)

90th% for body weight in kilograms =

= (-0.000021 * ((months)^4)) + (0.0019665 * ((months)^3)) - (0.067314 * ((months)^2)) + (1.1987668 * (months)) + 3.9439275)

95th% for body weight in kilograms =

= (-0.00002 * ((months)^4)) + (0.0019164 * ((months)^3)) - (0.06713 * ((months)^2)) + (1.2146142 * (months)) + 4.2059005)

Distribution of Weight by Month

If the same data is analyzed for each month, then the percentile represented by a given weight can be derived. Initially third and fourth order polynomial equations were tried, but were found to be inaccurate. Using 2 second order polynomials for above and below the 50th percentile gave equations adequate for most clinical situations.

Age 0 - 3 years, 5 to 50%ile

age in years

wgt^2

wgt

coefficient

0

74.5744670

-370.9007

465.67137

0.08

21.5263240

-120.2143

169.66209

0.25

10.5305620

-80.35502

154.04912

0.5

11.4926560

-134.0915

394.47192

0.75

12.6641000

-184.3957

675.51028

1

10.9348230

-177.0522

720.52022

1.5

6.6022349

-115.2368

503.11548

2

4.1042496

-73.07856

319.46719

2.5

3.2564507

-61.57435

283.19839

3

3.0926872

-64.76866

334.09184

Age 0 - 3 years, 51 to 95%ile

age in years

wgt^2

wgt

coefficient

0

-47.73194

406.68266

-770.0074

0.08

-21.5426

249.83756

-625.4028

0.25

-12.68309

201.34344

-700.376

0.5

-11.40127

225.28386

-1015.893

0.75

-9.973189

226.44153

-1188.366

1

-8.337609

209.26651

-1215.219

1.5

-6.166639

176.48147

-1162.968

2

-6.204415

190.50054

-1364.871

2.5

-6.521674

212.60027

-1637.347

3

-5.674029

198.50935

-1641.415