Trying to forecast the future

[Rick Pusateri]

I need help with a re-forecast I’m trying to create. As you can see from
the table, the planned % Subset of Total from Feb 06-Dec 06 do not look
like they will follow the historical trend. What I want to do is
re-forecast the subset column, based upon the % Subset of Total in
prior years/months. I know there must be a statistical formula(s) that
I should use, but I can’t figure out which one(s). Thanks in advance!

Year_ Mo_ Total Subset % Subset of Total
Y2003 Jan 1,845 39 2.1%
Y2003 Feb 1,792 32 1.8%
Y2003 Mar 1,953 48 2.5%
Y2003 Apr 1,912 55 2.9%
Y2003 May 1,837 57 3.1%
Y2003 Jun 1,888 55 2.9%
Y2003 Jul 2,009 52 2.6%
Y2003 Aug 1,991 52 2.6%
Y2003 Sep 2,105 41 1.9%
Y2003 Oct 2,128 51 2.4%
Y2003 Nov 1,867 40 2.1%
Y2003 Dec 2,069 36 1.8%
Y2004 Jan 2,182 41 1.9%
Y2004 Feb 2,145 51 2.4%
Y2004 Mar 2,356 74 3.2%
Y2004 Apr 2,250 73 3.2%
Y2004 May 2,071 67 3.3%
Y2004 Jun 2,239 75 3.4%
Y2004 Jul 2,348 72 3.1%
Y2004 Aug 2,359 73 3.1%
Y2004 Sep 2,376 66 2.8%
Y2004 Oct 2,317 57 2.4%
Y2004 Nov 2,236 57 2.6%
Y2004 Dec 2,229 26 1.2%
Y2005 Jan 2,459 53 2.2%
Y2005 Feb 2,387 64 2.7%
Y2005 Mar 2,517 85 3.4%
Y2005 Apr 2,372 79 3.3%
Y2005 May 2,308 85 3.7%
Y2005 Jun 2,307 89 3.9%
Y2005 Jul 2,375 81 3.4%
Y2005 Aug 2,452 85 3.5%
Y2005 Sep 2,408 63 2.6%
Y2005 Oct 2,338 57 2.5%
Y2005 Nov 2,241 63 2.8%
Y2005 Dec 2,089 60 2.9%
Y2006 Jan 2,367 51 2.2%
Y2006 Feb 2,482 81 3.3%
Y2006 Mar 2,503 82 3.3%
Y2006 Apr 2,568 86 3.4%
Y2006 May 2,562 84 3.3%
Y2006 Jun 2,459 81 3.3%
Y2006 Jul 2,434 81 3.3%
Y2006 Aug 2,572 83 3.2%
Y2006 Sep 2,576 84 3.2%
Y2006 Oct 2,663 88 3.3%
Y2006 Nov 2,641 85 3.2%
Y2006 Dec 2,550 82 3.2%


Rick Pusateri
Tel: (206) 925-1689
Fax: (206) 545-6091
Email: (e-mail address removed)

 

[Gary''s Student]

I plotted you total vs time and your % vs time.

Your total is growing at a nice linear rate:

T=14.779*M+1881.9 where M is one month units

Your % is converging to around 3.2%

I would forecast using the linear growth in total and a fixed percent of 3.2%

 

[Rick Pusateri]

Thanks, Gary - appreciate your response. The problem I see is that there
is seasonality to the numbers, and the % subset is growing overall. How
does your equation factor that piece in? Thanks!

Rick