This presentation provides an alternate way of getting confidence intervals for proportions. We have at least one problem in Week 6 where this applies. Rather than using Minitab, I have an Excel template that will help. Instructions on obtaining the file are at the end of the presentation.

1. HELP ON WEEK 6 HW
NUMBER 19
B Heard
Don’t steal my stuff…
Students can download
one copy for their own
use.

2. HELP ON WEEK 6 HW NUMBER 19
Number 19 is a pretty easy problem if you know what to look for and
use. However, it can be frustrating…
They want us to find the 90% Confidence Interval for each country

3. HELP ON WEEK 6 HW NUMBER 19
First let’s look at the problem again.
Ok, for Country A, 2005 adults were surveyed. The percentage for Country A is
71% So the p̂ for Country A is 0.71. What is 71% of 2005? (0.71)(2005) = 1403.5.
This bothers me because I would like a more accurate percentage. However I
have a little Excel Spreadsheet that will nail this one every time. I don’t like
switching back and forth between Minitab and Excel, but on this one – it just
makes it easier.

4. HELP ON WEEK 6 HW NUMBER 19
You can message me here at the Stat Cave to get a copy of this Excel
template (I will show you how at the end). I would have just uploaded
during the lecture, but it’s something new I was playing around with.
First I want to show it to you.

5. HELP ON WEEK 6 HW NUMBER 19
Here is what it looks like…
I put the
Sample
Size here
I put the
Sample
Proportion her
It is set up to
give you the 3
most requested
Confidence
Intervals, but
you can choose
a different one
in the last green
cell

6. HELP ON WEEK 6 HW NUMBER 19
They are asking for the 90% confidence interval for each Country. The
spreadsheet makes it a piece of cake and does the calculations just
like you would do them by hand.

7. HELP ON WEEK 6 HW NUMBER 19
Remember there were the following numbers of people surveyed from each
country.
Country A 2005
Country B 1234
Country C 987

8. So the 90% Confidence Interval for Country A would be (0.693, 0.727)
rounded to three decimal places…

9. HELP ON WEEK 6 HW NUMBER 19
Similarly for Country B
Country B 1234
So the answer would be (0.802, 0.838)
ALWAYS REMEMBER TO HIT THE ENTER
BUTTON AFTER PUTTING IN A NEW VALUE
INTO A GREEN CELL

10. HELP ON WEEK 6 HW NUMBER 19
Similarly for Country C
Country C 987
So the answer would be (0.950, 0.970)
ALWAYS REMEMBER TO HIT THE ENTER
BUTTON AFTER PUTTING IN A NEW VALUE
INTO A GREEN CELL

11. HELP ON WEEK 6 HW NUMBER 19
So it automatically gives me the 99, 95 and 90% confidence intervals.
If I wanted something funky like the 75% confidence interval, I would
enter it in that last cell on the left at the bottom.

12. HELP ON WEEK 6 HW NUMBER 19
Always read the question carefully, they may ask you for the 99%,
95%, 90% or some other confidence
I still like Minitab, but the issue with the exact number kind of throws
you on this problem, so I decided to use this Excel template.
Next page…

13. HELP ON WEEK 6 HW NUMBER 19
Since this is an Excel document, the only way I can get it to you is
through a message in the Stat Cave
Just Click Message
and say “Brent,
send me the
Confidence
Interval for
Proportions” Excel
File
Also See Next
Chart

14. HELP ON WEEK 6 HW NUMBER 19
Please note that I will check a couple of times for requests… It might
take me a few hours. Also remember that I am not a “personal tutor,”
I just enjoy helping you. This is something I did for fun and wanted
to share it with you…
As always, if you want to say thanks…
Be nice to an animal..
Don’t Litter…
Watch my YouTube Videos and give them a Thumbs Up on the
YouTube Sight (Links on Following Page)

15. HELP ON WEEK 6 HW NUMBER 19
Links
https://www.youtube.com/watch?v=zEzomXq43g0
https://www.youtube.com/watch?v=x9vsoP8wLAM
https://www.youtube.com/watch?v=q4993u8ZRdY
https://www.youtube.com/watch?v=SbXeza5v4b0
Thanks!