ACTIVITY 9
 Solutions
Activity 9.1
For mean confidence intervals we call into use
Table A2
which can be found in this
week’s folder.
The first concept to understand is the idea of Degrees of Freedom (DF).
For our
activity today, since we are only concerned with
one mean
(either from one sample of a difference
between paired data), DF = sample size – 1 (i.e. n – 1).
When finding confidence intervals,
Table A2
provides the
t multiplier (t*)
for the confidence interval expression:
if data is consists of only one sample
if data involves looking at the differences between paired data.
NOTE: you will notice that the DF column in this tables only increases by 1 from 1 to 30.
After that
the increments vary.
If your DF is NOT found in the table then conservatively use the CLOSEST
df in the table that does not exceed the DF of interest.
For example, if the degrees of freedom were
37 then from the table use 30.
Find tmultipliers and DF from Table A2 for the following conditions:
Confidence Level 90%, n = 25:
t* =
1.71
DF =
24
Confidence Level 95%, n = 25:
t* =
2.06
DF =
24
Confidence Level 95%, n = 35:
t* =
2.04
DF =
34
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 '08
 BARROSO,JOAOR
 Statistics, Degrees Of Freedom, Student's tdistribution

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