Over the past 100 years or so, people in industrialized societies have been maturing earlier, as well as growing heavier and taller than in the past. this phenomenon is referred to as the secular trend. the most likely explanation for the secular trend is

Consistent tendencies during a time period.

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changes in factors like average income and preferences can cause an entire demand curve to shift right or left. this causes a higher or lower quantity to be demanded at a given price. demand curves relate the prices and quantities demanded assuming no other factors change. it is important for consumers to know this information, because it is crucial for them to know what they can afford and can't afford. i hope this .