Microsoft Office Tutorials and References

In Depth Information

Now, you need to ﬁnd the lower limit and the upper limit of the 95% conﬁdence

interval for this study.

We will use Excel’s TINV function to do this. We will assume that you want to

be 95% conﬁdent of your results.

F21:

═

─

TINV(1-.95,24)*D16

Note that this TINV formula uses 24 since 24 is one less than the sample size of

25 (i.e., 24 is n-1). Note that D10 is the mean, while D16 is the standard error of the

mean. The above formula gives the
lower limit of the conﬁdence interval, 26.92
.

F23:
═
D10
þ
TINV(1-.95,24)*D16

The above formula gives the
upper limit of the conﬁdence interval, 29.42.

Now, use number format (two decimal places) in your Excel spreadsheet for the

mean, standard deviation, standard error of the mean, and for both the lower limit

and the upper limit of your conﬁdence interval. If you printed this spreadsheet now,

the lower limit of the conﬁdence interval (26.92) and the upper limit of the

conﬁdence interval (29.42) would “dribble over” onto a second printed page

because the information on the spreadsheet is too large to ﬁt onto one page in its

present format.

So, you need to use Excel’s “Scale to Fit” commands that we discussed in

Chapter 2
(see Sect. 2.4) to reduce the size of the spreadsheet to 95% of its current

size using the Page Layout/Scale to Fit function. Do that now, and notice that the

dotted line to the right of 26.92 and 29.42 indicates that these numbers would now

ﬁt onto one page when the spreadsheet is printed out (see Fig.
3.4
)

Note that you have drawn a picture of the 95% conﬁdence interval beneath cell

B26, including the lower limit, the upper limit, the mean, and the reference value of

28 mpg given in the claim that the company wants to make about the car’s miles per

gallon performance.

Now, let’s write the conclusion to your research study on your spreadsheet:

D10

C33:

Since the reference value of 28 is inside

C34:

the conﬁdence interval, we accept that

C35:

the Chevy Impala does get 28 mpg.

Important note: You are probably wondering why we wrote the conclusion on

three separate lines of the spreadsheet instead of writing it on one long line. This is

because if you wrote it on one line, two things would happen that you would not

like: (1) If you printed the conclusion by reducing the size of the layout of the page

so that the entire spreadsheet would ﬁt onto one page, the print font size for the

entire spreadsheet would be so small that you could not read it without a

magnifying glass, and (2) If you printed the spreadsheet without reducing the

page size layout, it would “dribble over” part of the conclusion to a separate

page all by itself, and your spreadsheet would not look professional.

Your research study accepted the claim that the Chevy Impala did get 28 miles

per gallon on the highway. The average miles per gallon in your study was 28.17.

(See Fig.
3.5
)

Save your resulting spreadsheet as:
CHEVY7

Search JabSto ::

Custom Search