Research Methodology - Dr. Krishan K. Pandey

166 Research Methodology
(iii) Standard error of standard deviation when population standard deviation is known:
σ
σ s
=
σ
p
2 n
(iv) Standard error of standard deviation when population standard deviation is unknown:
σ
σ s
where σ s =
=
σ
2
s
n
ΣdXi− Xi
2
n − 1
n = number of items in the sample.
(v) Standard error of the coeficient of simple correlation:
σ r
1 − r
=
n
where
r = coefficient of simple correlation
n = number of items in the sample.
(vi) Standard error of difference between means of two samples:
(a) When two samples are drawn from the same population:
F
HG
2 1 1
σ X X σ
i − = p +
2 n n
2
1 2
(If σ p is not known, sample standard deviation for combined samples eσs1⋅ 2j
*
may be substituted.)
(b) When two samples are drawn from different populations:
σ
σp σ p
− = +
n n
X X
1 2
I
KJ
2
d i d i
1 2
1
(If σ p1 and σ p2 are not known, then in their places σ s1 and σ s2 respectively may
be substituted.)
(c) In case of sampling of variables (small samples):
(i) Standard error of mean when σ p is unknown:
2
2