The following appeared as part of a promotional campaign to sell advertising space in the Daily Gazette to grocery stores in the Marston area．“Advertising the reduced price of selected grocery items in the Daily Gazette will help you increase your sales．Consider the results of a study conducted last month．Thirty sale items from a store in downtown Marston were advertised in the Gazette for four days．Each time one or more of the 30 items was purchased，clerks asked whether the shopper had read the ad．Two-thirds of the 200 shoppers asked answered in the affirmative．Furthermore，more than half the customers who answered in the affirmative spent over $100 at the store.” Discuss how well reasoned..．etc.
The conclusion of this argument is that advertising the reduced price of selected items in the Daily Gazette will result in increased sales overall．To support it，the author cites an informal poll conducted by sales clerks when customers purchased advertised items．Each time one or more of the advertised items was sold，the clerks asked whether the customer had read the ad．It turned out that two-thirds of 200 shoppers questioned said that they had read the ad．In addition，of those who reported reading the ad，more than half spent over $100 in the store．This argument is unconvincing for two reasons.
To begin with，the author's line of reasoning is that the advertisement was the cause of the purchase of the sale items．However，while the poll establishes a correlation between reading the ad and purchasing sale items，and also indicates a correlation，though less significantly，between reading the ad and buying non-sale items，it does not establish a general causal relationship between these events．To establish this relationship，other factors that could bring about this result must be considered and eliminated．For example，if the four days during which the poll was conducted preceded Thanksgiving and the advertised items were traditionally associated with this holiday，then the results of the poll would be extremely biased and unreliable.
Moreover，the author assumes that the poll indicates that advertising certain sale will cause a general increase in sales．But the poll does not even address the issue of increased overall sales；it informs us mainly that，of the people who purchased sales items，more had read the ad than not．A much clearer indicator of the ad's effectiveness would be a comparison of overall sales on days the ad ran with overall sales on otherwise similar days when the ad did not run.
In sum，this argument is defective mainly because the poll does not support the conclusion that sales in general will increase when reduced-price products are advertised in the Daily Gazette．To strengthen the argument，the author must，at the very least，provide comparisons of overall sales reports as described above.