Please advise..

I have collected 6 years of meeting registration data for about 400 meetings. I have the number of meeting registrants counted 24 weeks out from the date of the meeting. So for meeting abc I have something like this:

No. of weeks out No. of Registrants
6 3
5 6
4 11
3 17
2 22
1 20
0 24

Total Attendees: 103

Some meetings I have data for many weeks out for others the weeks out duration is a shorter-span (like the example above). My question is this:

If I have a meeting not yet started and it is say 3 weeks out from the meeting date. Can I predict what the final meeting attendee count is likely to be for the meeting 3 weeks away?

What type of analysis should I use? I am looking for my old college statistics textbook and have never felt so dumb. Thanks for any help or direction.


TS Contributor
For each meeting, compute the cumulative number of registrants for the number of weeks away, and divide that by the total number of final registrants to get a %. Then, for example, if you wanted to predict the final tally when the meeting is 3 weeks away, take all of your 3-week-out cumulative percentages and compute the average and standard deviation.

If, for example, on average, 38% of the people who attend have registered by the 3-week-out date, and there is a standard deviation of, lets say 5%, then a reasonable prediction band could be the mean +/- 2 standard deviations:

38% +/- (2 * 5%) = 28% - 48%

To predict the final attendance number, multiply the number representing 28% by 3.57 to get the lower end of the prediction band (28*3.57 = 100), and then multiply 48% by 2.08 (48*2.08 = 100) to get the upper end of the prediction band.
Follow-up Question

I still need to ask one more question.

I have calculated my cumulative percent registered for each week out for each meeting.

I have the mean and the standard deviation for each week out.

I do not understand in the last paragraph of the response where the 3.57 or the 2.08 come from. How do I calculate these? And what is the ‘number representing 28%’ exactly? Is that the number registered at 3 weeks out for the meeting I am predicting?

Thanks again for any assistance.