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In economics, demand is the utility for a good or service of an economic agent, relative to his/her income. (Note: This distinguishes "demand" from "quantity demanded", where demand is a listing or graphing of quantity demanded at each possible price. In contrast to demand, quantity demanded is the exact quantity demanded at a certain price. Changing the actual price will change the quantity demanded, but it will not change the demand, because demand is a listing of quantities that would be bought at various prices, not just the actual price.) Demand is a buyer's willingness and ability to pay a price for a specific quantity of a good or service. Demand refers to how much (quantity) of a product or service is desired by buyers at various prices. The quantity demanded is the amount of a product people are willing or able to buy at a certain price; the relationship between price and quantity demanded is known as the demand. (see also supply and demand). The term demand signifies the ability or the willingness to buy a particular commodity at a given point of time, ceteris paribus. Utility preferences and choices underlying demand can be represented as functions of cost, benefit, odds and other variables. ==Determinants of (Factors affecting) demand== Innumerable factors and circumstances could affect a buyer's willingness or ability to buy a good. Some of the more common factors are: :Good's own price: The basic demand relationship is between potential prices of a good and the quantities that would be purchased at those prices. Generally the relationship is negative meaning that an increase in price will induce a decrease in the quantity demanded. This negative relationship is embodied in the downward slope of the consumer demand curve. The assumption of a negative relationship is reasonable and intuitive. If the price of a new novel is high, a person might decide to borrow the book from the public library rather than buy it. :Price of related goods: The principal related goods are complements and substitutes. A complement is a good that is used with the primary good. Examples include hotdogs and mustard, beer and pretzels, automobiles and gasoline. (Perfect complements behave as a single good.) If the price of the complement goes up the quantity demanded of the other good goes down. Mathematically, the variable representing the price of the complementary good would have a negative coefficient in the demand function. For example, Qd = a - P - Pg where Q is the quantity of automobiles demanded, P is the price of automobiles and Pg is the price of gasoline. The other main category of related goods are substitutes. Substitutes are goods that can be used in place of the primary good. The mathematical relationship between the price of the substitute and the demand for the good in question is positive. If the price of the substitute goes down the demand for the good in question goes down. :Personal Disposable Income: In most cases, the more disposable income (income after tax 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. :Nature of the good: If the good is a basic commodity, it will lead to a higher demand * 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Demand」の詳細全文を読む スポンサード リンク
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