This argument states that the increased use salicylates as a food preservative could be the reason to have steady decline in the number of headaches suffered by the citizen of Mentia. Argument reaches to this conclusion based on twenty year study with the participant from Mentia. However, four pieces of evidence are specifically required to make further assessment of this argument.
In the first sentence author is trying to prove salicylates can be used to treat headaches, and this implication is drawn only because it shares same family with aspirin. Even though, salicylates and aspirin may belong to same family but this does not necessarily implies that salicylates will have same effect as aspirin, this assumption of salicylates have same effect as aspirin is too far fetched.
As stated by author many foods are naturally rich in salicylates, therefore citizens of Mentia have been subjected to salicylates from a long time even before food-processing companies started using salicylates as a food preservative. Hence, how much of this additional salicylates can affect their health? is debatable. Information about the increase in salicylates consumpption is required to correctly gauge if it is indeed the reason for steady decline in headache complaints.
The study was conducted over a period of twenty years. A lot can change in this 2 decades, along with the information given by author, it is necessary to consider other factors like pollution level, population growth or decrease, economical condition regarding to Mentia. Without the evidence of any change in forementioned factors, we cannot say the increase in use of salicylates is the only reason to have less complaints about headache.
Without the evidence diversity among of participant of this study, we cannot conclude the observation of this study will not hold water when it comes to population of Mentia. It may be a case that participants of this study, are of a same age group, same gender. Also the number of participant in this study is missing, without this we will not know whether or not this study had enough number of participants to draw any conclusion about residents of Mentia.
In conclusion, unless the four pieces of evidence aforementioned are presented