|
Null hypothesis: Ho:
There is no real difference between
the two reservoirs
in terms of their nitrate levels. Any
observed difference is therefore due to chance
(random error)". Ho: xA
=
xB
Data: Reservoir A
n=12, =
35.2 ppm s=
8.4 ppm
Reservoir B
n=12, =
27.0 ppm
s= 7.1 ppm
Analysis:
| xA
-
xB
|
8.2
t
=
----------------
=
-----------
=
2.583
﴾SxA- xB﴿ 3.175
calculated t = 2.583
critical t(0.05, 22df) = 2.07
t(calc)
exceed the t(crit) for 0.05 , also 0.02 . Therefore reject Ho.
Summary: There was a difference observed between the two
reservoirs in terms of the nitrate levels. A showed mean 35.2 ppm and
B showed 27.0 ppm. This difference was statistically
significant at the 0.02 level and is unlikely (less than 2% likely) to
have occurred by chance alone. We can reject the null hypothesis as stated above, and
conclude that on the basis of the data provided, a real difference exists
between the two reservoirs' nitrate levels.
(xA
-
xB):
8.2 ppm,
22 df t: 2.583 ,
P < 0.02
|