a, = number of plots per stratum j 
Pj = area proportion of stratum j of Ac 
Yı3 = volume of plot i of stratum j (n3 plot) 
T = number of strata 
2 2 
Estimate of variance: s^ = 2 P,s, ee em hir p Wine = VA) 
j 2 
n. 
J [7 vs] 
y Eur ATE MISERAT eM 
2 2. Ti; n 
Estimate of variance of stratum J S. = 
j (n.- 1) 
The two-stage unequal probability (PPS) sampling 
M 
> v 
m à 
j 3, 
Estimate of total volume : ve —— 2x (m O40, Nu M Seu. (5) 
J 
in which M = number of primary units (PU) in the population on Ac 
m = number of PU's in sample 
v5 = volume of PU, 25) 
x, = area of PU, (ha) 
j J 
and estimate of variance of total volume: 
2 omm 
; AN E: 
Sy = - «s. (6) 
t (m- cu 
When all PU's are used, for total volume: ve = 2.9; . 1... 2 €) 
and for variance (with a given weight) of total volume: 
  
   
The tw 
Estima 
Plot v 
which 
b = re 
Regres 
Estima 
Estima 
in whi