I'm trying to find the best way to present average giving to an organization based on how much had been given in previous years, but I realized that different methods of averaging give me different percentages. I understand why I get different figures, but I'm having a hard time wrapping my head around why that is and what those different figures mean. To give context, I'm comparing year-to-date giving across the five previous years to see where we should be by this point in our current year. So, for example, I should be able to say we should have received x% of our giving by this point in the current year, and therefore make a recommendation of how we should focus future efforts for the rest of the year. I'm applying this problem across a number of different groups of donors, but the core of the problem remains the same.
I'll refer to the raw data in the following way: C=Current (Year-to-date) giving. C1-C5 refer to the five previous years, and CN refers to that giving in the current year (N=Now). T=Total giving, so T1-T5 refer to the total giving in those previous years. What I'm trying to find is PN, or the percentage of total giving I should have in the current year. I'm using the percentage I'll generate to compare to two different figures: the average of total giving in the five previous years, and the goal set at the beginning of the current year. Which of the following methods would be best, or should I use a different method? What are the implications for the different methods?
I'll refer to the raw data in the following way: C=Current (Year-to-date) giving. C1-C5 refer to the five previous years, and CN refers to that giving in the current year (N=Now). T=Total giving, so T1-T5 refer to the total giving in those previous years. What I'm trying to find is PN, or the percentage of total giving I should have in the current year. I'm using the percentage I'll generate to compare to two different figures: the average of total giving in the five previous years, and the goal set at the beginning of the current year. Which of the following methods would be best, or should I use a different method? What are the implications for the different methods?
- Method 1: Average the percentages. Find P1-P5. That is, C1/T1=P1. After this is done for all five previous years, (P1+P2+P3+P4+P5)/5=PN
- Method 2: Percent of the averages. ((C1+C2+C3+C4+C5)/5)/((T1+T2+T3+T4+T5)/5)=PN
- Method 3: Percent of raw figures (no averaging). (C1+C2+C3+C4+C5)/(T1+T2+T3+T4+T5)=PN