Yeah, but they arent trying to predict the outcome of the game. They're trying to predict the gambling public's perception of the likely outcome of the game. And as more information has become available to everyone, the gambling public's perception has gotten more accurate, thus the spreads appear more accurate.
This is all correct. Each sportsbook utilizes multiple handicappers that they’ll pay out a nominal fee for their assessment. Each handicapper will have his own system of breaking down the data to determine the point spread of each game. One sports book might take the average of all their handicappers info. Another might throw out the highest and lowest, and take the average of whats left. Another may take the median. In any case, the books are going to have slight variation with each other, but not much.
A handicapper in Vegas is really no different than a financial analyst for stocks at Goldman Sachs, they are just looking at different data. Both are providing a valuation based on likelihood of future outcomes, given past data that is publicly available.
The money line is another story, they are set directly by the sports books based on the aggregate data provided by all the handicappers. Generally speaking, the wider the range of outcomes, the bigger the ML payout.
Example - Team A plays Team B. 5 handicappers yield an average of Team A being favored over Team B by 7.5 points. Highest is 9 points, lowest is 6 points. Then you have Team C vs. Team D. Average of 5 handicappers also have Team C favored by 7.5, but in this case the highest is 11.5 and the lowest is 3.5. Both spreads are the same, but Team C vs. Team D is going to have a bigger ML due to higher degree of uncertainty around the game from the experts.
Another point of order - while the general goal for sportsbooks is to even out the the bets on both sides of the spread on any given game, the ultimate goal is really just to even out the money on both sides when looking at the sum total of ALL games. If 80% of money is on Tennessee to cover over this weekend, but 80% of money is on another underdog somewhere else to cover, then its a wash, and they won’t necessarily move either line even though the bets are uneven. However, they still might move both lines if they see the betting traffic slow down, just to increase total number of bets. General point is that uneven betting doesn’t always yield a line movement.
Back in the pre internet days, there was basically one guy in Vegas who set the opening lines. He was very knowledgeable about football, but he was going with his gut. Whole number spreads were common back then, too.
This is actually not quite the case….very oversimplified. It’s absolutely never been “a single guy going off his gut”. Even way before the internet, there were multiple handicappers with spreadsheets, statistics, and advanced metrics that they had studied over years. The system for setting the lines was largely the same as it is now. The only difference now is that there is a lot more data available, and it travels faster and can be analyzed faster. Therefore, accuracy has certainly improved.
I read an article about Earl Weaver a few months ago, the HoF MLB manager who was known as perhaps the earliest adopter of analytics in baseball back in the 70’s. He credited his father, who was a bookie / handicapper, as a major credit to his success based on advanced metrics he used to set lines for games in the Great Depression and WWII era. Said he had hundreds of pages of data on every MLB season, mostly all handwritten. There were hundreds if not thousands of guys just like Earl Weaver’s dad, even in the 1930’s and 40’s. Its never been a situation where the handicappers / bookies are just flying by the seat of their pants. They’d all lose their asś pretty quickly if that’s all they did.