¿mièti 
- 220 - 
and similarly: 
q + 
p • q . c 
For the second condition: a minimum standard error for a given expenditure, the 
2 
values for n and n are calculated, setting S at a minimum: 
g p 
C = n c + n c 
t g g PP, 
for which we derive: 
C - n c C, - n c 
-Î S_£L and n = -Î e_£. 
c g c„ 
As given above: 
s 2 = -* 
_SL 
T1 
Substituting n^ = 
C, - n c 
_g_£. 
gives: 
s 2 =-E- 
C, - n c 
t g g 
Differentiating for n , and equating the result to zero results in: 
■ t Ip 
Jq. e . c + c JJ 
and similarly: 
Ip. c . c + c 
« g P P 
/i 
For both conditions the optimum proportion of field-photo plots, given a fixed 
ratio of field/photo costs, can be calculated. For both conditions this proportion 
equals: 
p.q. c 
P + 
_S_ 
p. q. c 
K. 
2 2 
p. q. c + p . c . c 
E 2 g 
p. q. c + q . c . c 
g P g