### Description

The distribution of body weight for young girls 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

2.36

2.58

2.93

3.23

3.52

3.64

3.81

1

2.97

3.22

3.59

3.98

4.36

4.65

4.92

3

4.18

4.47

4.88

5.4

5.9

6.39

6.74

6

5.79

6.12

6.6

7.21

7.83

8.38

8.73

9

7

7.34

7.89

8.56

9.24

9.83

10.17

12

7.84

8.19

8.81

9.53

10.23

10.87

11.24

18

8.92

9.3

10.04

10.82

11.55

12.3

12.76

24

9.87

10.26

11.1

11.9

12.74

13.57

14.08

30

10.78

11.21

12.11

12.93

13.93

14.81

15.35

36

11.6

12.07

12.99

13.93

15.03

15.97

16.54

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

5th% for body weight in kilograms =

= ((-0.000007 * ((months)^4)) + (0.0008141 * ((months)^3)) - (0.033894 * ((months)^2)) + (0.7610993 * (months)) + 2.2805025)

10th% for body weight in kilograms =

= ((-0.000008 * ((months)^4)) + (0.0008763 * ((months)^3)) - (0.035785 * ((months)^2)) + (0.7871032 * (months)) + 2.5045076)

25th% for body weight in kilograms =

= ((-0.000008 * ((months)^4)) + (0.0008543 * ((months)^3)) - (0.035339 * ((months)^2)) + (0.8069777 * (months)) + 2.8537413)

50th% for body weight in kilograms =

= ((-0.000008 * ((months)^4)) + (0.000942 * ((months)^3)) - (0.039113 * ((months)^2)) + (0.8750996 * (months)) + 3.1727893)

75th% for body weight in kilograms =

= ((-0.000012 * ((months)^4)) + (0.0012394 * ((months)^3)) - (0.047108 * ((months)^2)) + (0.9683973 * (months)) + 3.4630431)

90th% for body weight in kilograms =

= ((-0.000015 * ((months)^4)) + (0.0015248 * ((months)^3)) - (0.055114 * ((months)^2)) + (1.0707593 * (months)) + 3.6361131)

95th% for body weight in kilograms =

= ((-0.000017 * ((months)^4)) + (0.0016508 * ((months)^3)) - (0.058214 * ((months)^2)) + (1.1077472 * (months)) + 3.8491879)

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.

0 to 3 years, 5 to 50%ile

Age in years

wgt^2

wgt

constant

0

51.4975130

-236.81980

277.43047

0.08

31.7763770

-176.23790

248.09476

0.25

17.3920040

-129.32670

241.35898

0.5

12.4423640

-129.72300

338.63512

0.75

10.0010610

-126.56140

400.63952

1

8.5316185

-121.47250

432.82506

1.5

7.3561926

-121.59500

504.41654

2

7.0404320

-131.32900

615.69639

2.5

6.7795130

-140.07040

727.51743

3

5.1141372

-111.33930

608.52826

0 to 3 years, 51 to 95%ile

Age in years

wgt^2

wgt

constant

0

-59.976060

502.25993

-946.9905

0.08

-36.374870

372.31023

-855.846

0.25

-19.526170

270.62484

-841.9886

0.5

-12.228280

224.64363

-934.0595

0.75

-9.691979

209.58069

-1033.888

1

-9.365721

220.86997

-1204.301

1.5

-8.886865

232.64042

-1426.692

2

-6.713345

195.00787

-1319.883

2.5

-4.625871

149.48733

-1109.546

3

-3.757316

131.81509

-1057.16

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