and receipt of benefits) a person has, the more likely that person is to buy. Tastes or preferences: The greater the desire to own a good the more likely one is to buy the good. There is a basic distinction between desire and demand. Desire is a measure of the willingness to buy a good based on its intrinsic qualities. Demand is the willingness and ability to put one's desires into effect. It is assumed that tastes and preferences are relatively constant. Consumer expectations about future prices, income and availability: If a consumer believes that the price of the good will be higher in the future, he/she is more likely to purchase the good now. If the consumer expects that his/her income will be higher in the future, the consumer may buy the good now. Availability (supply side) as well as predicted or expected availability also affects both price and demand. Population: If the population grows this means that demand will also increase. This list is not exhaustive. All facts and circumstances that a buyer finds relevant to his willingness or ability to buy goods can affect demand. For example, a person caught in an unexpected storm is more likely to buy an umbrella than if the weather were bright and sunny. The number of consumers in a market: The market demand for a good is obtained by adding individual demands of the present, as well as prospective consumers of a good at various possible prices. The larger the consumer-base is for a good, the greater the market demand for it. Demand function equation and curve The demand equation is the mathematical expression of the relationship between the quantity of a good demanded and those factors that affect the willingness and ability of a consumer to buy the good. For example, Qd = f(P; Prg, Y) is a demand equation where Qd is the quantity of a good demanded, P is the price of the good, Prg is the price of a related good, and Y is income; the function on the right side of the equation is called the demand function. The semi-colon in the list of arguments in the demand function means that the variables to the right are being held constant as one plots the demand curve in (quantity, price) space. A simple example of a demand equation is Qd = 325 - P - 30Prg +