[strombofulous]

> it is fun trying to find lines that have positive expected value

I've never gambled before, does this happen often? I would have assumed gambling companies wouldn't offer any bets like this, since it implies their EV is negative.

[dottrap]

Look up Edward Thorp, the famous mathematician who was the first to use probability theory to beat blackjack and write a book about it (Beat the Dealer). Basically, as a deck uses up cards, the remaining in the deck may present a positive expected value. By counting cards and knowing expected values, you can adjust your bets to capitalize.

Since Thorp, Casinos have made it harder to beat them (e.g. larger decks), but they still tease the possibility you can beat them to entice people to try (and lose).

Edward Thorp later went on to write Beat the Market, where he tried to apply similar probability principles to the stock market. He independently invented the options formula, before Black-Scholes (which the latter won a Nobel Prize).

[throwaway_4ever]

The only exception is Blackjack, where you could learn positive EV play in a week, by "counting cards". That's why casino's kick people playing too well. They make a little money off 99% of players playing bad and try to kick the 1% that make money off the casino.

[le-mark]

In sports positive EV can happen a lot based on real world circumstances. Hot streaks are real, injuries and line ups change before and even during games, players get arrested, etc. Often times opening lines move drastically because the books just don’t know the true odds. In practice the books move the line so they make a profit. Example everyone would bet on chiefs over lions by a touchdown all day long; a line might start there but move quickly. It’s quite amazing that final line is almost always 50/50 win probability.

[texaslonghorn5]

Where are you consistently finding books that close the moneyline at -110/-110?

[noduerme]

Sportsbooks don't make money by betting against the gamblers. They make money by facilitating betting between gamblers on both sides of the game. Their goal isn't to win, it's to set a line that'll attract an even amount of money on both sides, and keep a percentage for the service. So lines (the final scores you're betting on) move over time as the public piles on one side or another of a bet, and that there's often value in going the other way if you know enough about what a line should be.

[rileymat2]

Is this true if they are not the counter-party, but the facilitator?

[whartung]

Sports (parimutuel) gambling is different from casino gambling. There's no "house margin", rather they simply impose a fee (percentage) on the bet.

It's why on a 1:1 bet, you'd lose money, as the sportsbook tend to take something like 10%. Even though the odds are 1:1, your $1 bet would net $0.90. ($1.90, you'd get your dollar back.)