Tobias Buckell's unofficial poll of sf/f advances (with disclaimers). Interesting, and the numbers don't seem that foreign to my own experience. This also addresses one element of that oft-repeated "to be agented or not to be agented" question AKA So, What Can an Agent Do For Me Anyay?
Regarding first novels:
Broken down by Agented vs. Unagented:60% of our first time novelists had an agent, the other 40% sold the book without an agent, and a high number indicate they got agents right after or during the sale of the book.
The range in agented advances is from $1500 to $40,000
The average agented advance is $7379
The median agented advance is $5500
The range in unagented advances is from $0 to 13,500
The average unagented advance is $4611
The median unagented advance is $4000
These figures have noticeable differences across the board. Not having an agent looks to cost one well more than the agent's percentage on average, and certainly most of the higher ranging figures come from people with agents.
Regarding career writers with a number of novels:
Broken down by Agented vs. Unagented:15% of our authors with multiple books sold over multiple years had no agent, out of our sample size their results will have a margin of error of 32%, nonetheless the data is striking:
The range in agented advances is from $1000 to $600,000
The average agented advance is $36,455
The median agented advance is $12,500
The range in unagented advances is from $0 to $21,500
The average unagented advance is $14,143
The median unagented advance is $7500
These figures have noticeable differences across the board. Not having an agent looks to cost one well more than the agent's percentage on average, and certainly most of the higher ranging figures come from people with agents. The average advance via agent differs by as much as a factor of 3! Even with the 32% margin of error added in, the significance is fairly astounding.