The Yes/No prices that are displayed for a market simply represent the prices at which you’d need to purchase a contract to instantly get matched with another buyer. In other words, these prices are determined by the current bid and ask prices of the market. More concretely, the price of a Yes contract is simply the lowest price you could pay in order to get matched with a resting No order. In simple words, the prices reflect the percentage of people favouring a certain position. If the rate of a Yes share stands at 30, it essentially means 30% of the people in the world believe that yes will be the outcome of that event while the rest of the people (70%) think that the outcome of the event, on settlement, will be No.
These prices are not to be confused with the prices that show up on the market’s graph. The prices on the market graph represent the history of prices at which trades were executed.