An essay on "soy eating for preventing diseases"

Hello,

I wrote another essay, which is a GRE-type argument analysis. I present here both, the argument, which is not to be checked, since it's written by ETS, and my analysis of this argument, which presumably contains some errors. I'll be very obliged if you take a look and point some of these errors out.

Argument (should not be checked):

"A recent study shows that people living on the continent of North America suffer 9 times more chronic fatigue and 31 times more chronic depression than do people living on the continent of Asia. Interestingly, Asians, on average, eat 20 grams of soy per day, whereas North Americans eat virtually none. It turns out that soy contains phytochemicals called isoflavones, which have been found to possess disease–preventing properties. Thus, North Americans should consider eating soy on a regular basis as a way of preventing fatigue and depression."

Analysis:

This argument claims that North Americans suffer more chronic fatigue and chronic depression than Asians because Asians, on average, eat daily 20 grams of soy, which possesses some disease-preventive properties. There are several illogical points in the provided argument.

First, it does not indicate numbers of people, participated in the measurement on both continents. If too few people were tested, then the resulting statistics is unreliable. For example, if only three Americans were tested, and two of them by chance had depression, then it obviously will not be possible to project this healthy/ill proportion on the entire population of North America. The argument also does not take into account socio-economical environments in which tested people exist. If testing were performed among lower-class Americans and upper-class Asians, then the results may be significantly affected by this class gap, since people from lower social classes are more likely to suffer from depression because of the financial problems they experience. Thus, the argument does not provide any evidence that the taken samples of people in North America and Asia are representative and similar, that is, comparable.

Also, the argument implies that Asians suffer less because they eat soy, but there is no ground for this implication. It would be better if there were a comparison between similar Asians who eat soy and who do not.

The next illogical inference is that soy prevents exactly chronic fatigue and depression, though existent data do not report what kind of diseases soy prevents. And even if soy did prevent exactly these diseases for Asians, it would not guarantee that the same effect soy makes on North Americans, because organisms of American and Asian people are different in some ways, at least in what concerns the digestive system, which may affect soy impact on the organism.

Finally, even if soy might help North Americans prevent exactly the above mentioned diseases, there is no reason for eating soy every day as the analysis suggests. Maybe, soy will work efficiently enough if Americans eat it only once per week.

It may be concluded that the suggestion for North Americans to eat soy is premature, and the influence of soy on the organism of an average North American should be investigated much further.

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Thanks in advance.

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Victor