After studying a random sample of 1024 individuals who had smoked daily for at least three years and comparing the results of this study with the results of a study of 1024 individuals who had never smoked, a group of researchers concluded that habitual smoking causes increased difficulties in concentrating.
Which of the following, if true, most severely weakens the researchers' conclusion?
(A)The addiction to smoking and the cravings this addiction engenders is often on the mind of habitual smokers.
(B)Some non-smokers with attention deficit disorder (ADD), which causes an inability to concentrate, display even less ability to concentrate than some smokers.
(C)A separate research study found that smokers and non-smokers exhibited statistically significant differences in their incarceration rates.
(D)After developing a severe addiction to smoking for fifteen years, the ability of many individuals to concentrate is decreased.
(E)A separate research study found that individuals with preexisting attention and concentration disorders exhibited significantly higher rates of trying cigarettes and subsequently becoming addicted to smoking.![]()
Which of the following, if true, most severely weakens the researchers' conclusion?
(A)The addiction to smoking and the cravings this addiction engenders is often on the mind of habitual smokers.
(B)Some non-smokers with attention deficit disorder (ADD), which causes an inability to concentrate, display even less ability to concentrate than some smokers.
(C)A separate research study found that smokers and non-smokers exhibited statistically significant differences in their incarceration rates.
(D)After developing a severe addiction to smoking for fifteen years, the ability of many individuals to concentrate is decreased.
(E)A separate research study found that individuals with preexisting attention and concentration disorders exhibited significantly higher rates of trying cigarettes and subsequently becoming addicted to smoking.