Sales promotions result in an upward bump in sales during the promotion period. Because customers buy during sales promotions for reasons that may affect their purchases before and after the promotion, the company should evaluate the volume of sales for the sales promotion period plus an equal period before, and at least two equal periods after, the promotion. If the sales promotion lasts a week, the evaluation period should be at least four weeks, including one week before and two weeks after the promotion. This methodology catches possible dips before the promotion, if customers are waiting for the sale, as well as any continuing increase or decrease in sales volume after the promotion. The evaluation must also include the costs of the promotion over the evaluation period. If the company wishes to evaluate brand awareness, it must include a customer survey in the evaluation.