Seminar 2 
Unit 2

Confidence Interval

Hypothesis Testing

Analysis of Variance
Activity 2.1 –
Confidence Interval
Rozex Hotel has been sending its staff for customer service
training for the last two years. Recently, Rozex has conducted
a round of mystery guest survey to monitor the progress. The
survey scores is enclosed (
see Activity2.1_Data.xls
). The
industry average score
for the customer satisfaction
is 80
(out of a scale of 100).
Activity 2.1
In group of 4,
1. Use Excel to construct the
90%
confidence interval
for
the mean customer service scores.
2. Using answer in part 1, do you think there is
sufficient
evidence
to conclude that Rozex Hotel customer service
has met the industry standard?
You may refer to “Excel Self Practice Prior Seminar 2”
Practice 2.1.
Activity 2.1 > Data Analysis > Descriptive Statistics > OK
14
Activity 2.1 Debrief
Confidence Interval Estimates for
μ
Use
Z
distribution
If the
population
standard deviation
is
known
.
Use
t
distribution
If the
population
standard deviation
is
unknown
.
Note:
1. For the use of
Z
distribution, we require that
X
is normal or use a large
sample size to overcome this.
2. For the use of
t
distribution, we require
X
to be normal or nearly normal.
n
Z
X
s
a
2
/
±
n
s
t
X
n
1
,
2
/

±
a
Activity 2.1 Answer
Based on Excel Output, the 90% confidence interval is
(65.55, 73.39). This interval is
below 80
and did not
contain 80. Therefore, the customer service level of
Rozex Hotel is still
below the industry norm
despite the
training initiatives.
Score
Mean
69.46538
Confidence
Level(90.0%)
3.922194
Lowe Limit = 69.47 – 3.92 = 65.55
Upper Limit = 69.47 – 3.92 = 73.39
Activity 2.2 –
OneSample
t
Test
The McFarland Insurance Company Claims Department reports the mean
cost to process a
claim is $60
. An industry comparison showed this amount
to be larger than most other insurance companies, so the company
instituted costcutting measures. To evaluate the effect of the costcutting
measures, the Supervisor of the Claims Department selected a random
sample of 15
claims processed and the costs of claims are indicated in the
enclosed file (
see Activity2.2_Data.xls
).
At the
0.01 significance level
, is it reasonable to conclude that the mean cost
to process a claim is now
less than $60
?
Activity 2.2 Cont’d
Tasks:
In groups of 4 persons,
1. Follow the
5steps
procedure to conduct an
appropriate hypothesis testing.