QMS 202 Lecture Notes - Standard Deviation, Confidence Interval
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Summary of lecture 1
What is unknown? Population Mean and Population proportion.
What is known? Sample mean and sample proportion.
We can always take a sample of quantitative data (via survey)
and calculate the sample mean. We will use this sample mean to
construct an interval that will contain the population mean c% of
the time. This c% (i.e. 95%, 90%, 92% etc) indicates our
confidence that this interval will contain the (true) population
mean. We use this c% to calculate the z and t values (known as
critical values) where this c% is treated as "area under the
I have shown you two ways of calculating the confidence interval
1. Using the formula (refer to equation 10.1 on page 407 of the
2. Using the calculator function "INTR" (on page 409)
The third way of calculating the confidence interval is to use
SPSS (software) which was not shown in class but the
instructions are in my powerpoint slides.
When you select "INTR" function, you will encounter "Z" and "t".
Select "Z" if population standard deviation is given in the
Select "t" if population standard deviation is NOT given in the
Z and t are the critical values.
To find Z values, use "INVN" function and input "area" (which is
the confidence level (usually expressed in %); std dev=1; and
To find the t values, you have two options: (1) t table (which will
be provided in the quiz/test/exam) and (2) INVt function and
input "upper area", "df" (degree of freedom=n-1).
Does this help?