A popular modern economic theory is that if prices rise slowly over time, people will tend to purchase today instead of saving money to purchase tomorrow, since they believe the price of what they want will be higher tomorrow. If prices drop slowly over time, people will tend to save as long as possible before purchasing, since they believe the price of what they want will be lower tomorrow. Since simple economic productivity is measured by summing the amount of dollars spent, the theory is that for these reasons low inflation leads to productivity.