Porter — The Growth of St. Louis Children. 287 
principle. The percentile grades of the heights of girls, 
aged 9, are as follows: — 
TABLE No. 8. 
THE PERCENTILE DISTRIBUTION OF THE HEIGHTS OF GIRLS, AGED 9. 
, Number of : 
Percentile Grades. Obecrvatious. Heights. 
95 2015.9 133.42 Cm. 
90 1909.8 130.97 * 
80 1697.6 128.62 “ 
1591.5 127.58 “¢ 
70 1485.4 126.54 
1273.2 125.53‘ 
50 1061.0 124.11 
40 848.8 122.76 ‘ 
30 636.6 121.21.. * 
25 580.5 120.90 ‘ 
20 424.4 119.59 ** 
10 212.2 8 ease 
5 106.1 115.17‘ 
TOtal...2s ses ees 2122 
The Probable Error of the Average can be determined by 
means of the formula 
eos (5)* 
Vn 
where E = the probable error of the average, 
d = the probable deviation of an individual from the 
average, 
n = the number of observations in the series. 
Substituting the values determined for the heights of girls, 
aged 9, we have — 
3.698 
V 2122 
E= = + 0.079 cm. 
The values of E are given in Table No. 9. 
* Formulas (1), (2), (3) and (5) and Table No. 6 are taken from L. 
Stieda’s admirable article: Ueber die Anwendung der Wahrscheinlichkeits- 
rechnung in der anthropologischen Statistik. Archiv. fir Anthropologie, 
Bd. xiv., 1882, p. 167-182. 
