229 
ot volume, 
mean 
as: 
The total cost then equals: 
of g ( = 2. 2)J 
olume 
d as 
ird 
instead of = 
126 (11. 5) + 713 (0.37) 
1712.8 US $ 
170 (11. 5) + 290 (0. 37) 
2062. 3 US $ . 
In fig. 3 the standard error path of the mean growth S- (n + n ) is given for various 
n values. The number of photo plots (n ) belonging to these field plots are calculated 
g n p 
from the above given optimum ratio —^ = 5. 66. The values for S- (n + n ) are 
n g g g p' 
t t i. i j? o2 _ 0.3926 2 , nio1 2 1.6222 
calculated from S- = + 0.3131 . 
g^ n n 
n g p 
For the total standard error of the mean growth,' the standard error of the mean 
plot volume must also be considered. As the mean plot volume is calculated with 
the help of a newly constructed aerial volume regression, the standard error of the 
mean plot volume is calculated from : 
s| = 
n 
P 
6. 27' 
+ 0.2166 
28. 1403" 
n 
(see first application) using the 
P 
same n , and n values as calculated for the optimum proportion for the growth. 
§ P 
The thus calculated values for S- are indicated in fig. 3 as S- volume (n + n ). 
v n v g p ; 
P 
/2 2 2 
The combined effect of the two variances for the various n values: S- = S- + S- 
g g v g 
are indicated in fig. 3 as: S- growth + volume (n + n ) . 
g g P 
The cost path, which is given in fig. 3 as C (n + n ), allows the cost resulting 
f g P 
from the use of a certain n value to be read together with its n value. This cost 
g P 
is again given in man days and in US $ . 
In addition the standard error path of the mean growth S- (n ) is also given using 
field plots only. The data as given by STELLINGWERF (1973-5) are used for the 
calculation of the standard errors when the respective n g plots as given on the 
x-axis are considered. The standard deviation as calculated from n = 174 plots 
2 g - 
was given by STELLINGWERF: s- = 0. 3432; the mean growth was g 174 = 2. 23 
per cent. 
The standard error of the mean volume for n =40 plots for example then becomes: 
, g 
0.8041 x 120 
40 
1. 39 (= 6. 59 per cent of v^^ ).