In America alone, tipping is now a $16 billion-a-year industry. A recent poll showed that 40% of Americans【C1】______the practice. Tips should not exist. So【C2】______do they? The conventional wisdom is that tips both【C3】______the efforts of good service and reduce uncomfortable feelings of inequality. 【C4】______according to new research from Cornell University, tipping【C5】______serves any useful functions. The paper analyses data from 2,547 groups dining at 20 different restaurants. The【C6】______between larger tips and better service was very 【C7】______: only a tiny part of the 【C8】______in the size of the tip had anything to do with the quality of service. Customers who rated a meal as "excellent" still tipped 【C9】______ between 8% and 37% of the meal price. Tipping is better explained by culture than by economics. In America, the custom【C10】______ institutionalized: it is regarded as part of the【C11】______cost of a service. In a New York restaurant, failing to tip at least 15% could well mean【C12】______ from the waiter. Hairdressers can expect to get 15~20%, the man who【C13】______your groceries $2. In Europe, tipping is less common; in many restaurants, discretionary tipping is being 【C14】______by a standard service charge. In many Asian countries, tipping has never really 【C15】______at all. How to【C16】______ for these national differences? According to Michael Lynn, the Cornell paper"s co-author, countries in which people are more extrovert, sociable or neurotic tend to tip more. Tipping relieves 【C17】______about being served by strangers. And, says Mr. Lynn, "in America, where people are 【C18】______and expressive, tipping is about social approval. If you tip badly people think less of you." Icelanders, 【C19】______ , do not usually tip—a measure of their 【C20】______ , no doubt.