MINITAB Assignment on Confidence Intervals
The holiday season is fast approaching, how generous do Canadians feel at this time? A recent survey (IPSOS,
November 2015) in Canada investigated this topic. One question was “how likely are to donate to charity?”.
Out of 615 randomly selected Canadians, 173 responded “very likely”. ** You will use Minitab to find a
99% confidence interval and a 95% confidence interval for the population proportion, using the following
instructions. There will be points for good presentation, and points taken away for poor presentation (which
means write clearly and staple your pages!).
INSTRUCTIONS FOR MINITAB VERSION 17
1. Open Minitab and type your name and student ID in the Session window.
2. Find the 99% confidence interval by selecting Stat > Basic Statistics > 1 Proportion…, then select
Summarized data. Enter the appropriate values: the Number of events refers to the number of
“successes”; the Number of trials refers to the sample size. Next click on the Options… and change
Confidence level to 99 and Method to Normal approximation. Click OK, then OK.
3. Repeat Step 2 except under Options … type 95 in for the Confidence level.
4. Print off all the output that appears in the Session window.
Answer the questions on the next page in the space provided, and hand this in with your printout.
INSTRUCTIONS FOR MINITAB EXPRESS
1. Open Minitab Express.
2. Find the 99% confidence interval by selecting Statistics > One Sample > Proportion…, then select
Summarized data. Enter the appropriate values: the Number of events refers to the number of
“successes”; the Number of trials refers to the sample size. Next click on the Options… and change
Confidence level to 99 and Method to Normal approximation. Click OK, then OK.
3. Repeat Step 2 except under Options … type 95 in for the Confidence level. The output for Steps 2 and 3
will appear in the output window.
4. This final step is included to make sure you are submitting your own work and not copying someone else’s.
In the Minitab spreadsheet, go to Column C1 and row 1. Type Math2208 in this spot.
Express on PC: Next choose Data > To Text. Enter C1 in the box Recode values in the following
columns.
Express on Mac: Choose Data > Recode > To Text. Then enter C1 in the box values in the following
columns.
Under the box Recoded value replace Math2208 with your name and student number. Then hit OK. The
output will appear in the Output window. Select File > Print to print this output.
Print off all of your output.
Answer the questions on the next page in the space provided, and hand this in with your printout.
** The original survey used stratified sampling; the sample size has been adjusted for a simple random sample.
MATH2208
MINITAB Assignment on Confidence Intervals
NAME:
(a) 2 pts Is the sample size large enough to justify the method we used in MINTAB? i.e to justify use of
the normal approximation.
(b) 1 pt State the 99% confidence interval from the output. Highlight (or circle) it, and label it as (a) on the
output.
_________________________
(c) 2 pt What is the margin of error for your confidence interval?
Show your work.
(d) 4ps Interpret the interval from part (b), in context.
(e) 1 pt When reporting this interval, a journalist would typically describe the confidence level of 99% as
being accurate __________ times out of ______________ .
(Fill in the blanks appropriately.)
(f) 3 pts Based on the confidence interval, are we confident that more than 20% of Canadians feel they are
very likely to give to charity this year? Explain your answer.
(g) 2 pts State the 95% confidence interval from the output. Highlight (or circle) it, and label it as (f) on the
output.
(h) 1 pt How does the margin of error change?