Critical Reasoning

Advertisement: Do you want to be more energetic,
vigorous, and physically fit? Take a daily supplement
of Vita-plus, a vitamin combination containing
additional proprietary ingredients. Our studies using
hundreds of volunteers show that after just one week
of taking 2 capsules daily, participants report being
more energetic and alert on average than the average
level reported by the National Institutes of Health
survey of all Americans.
Which of the following would most strengthen the
advertisement's claim that Vita-Plus supplements
make one more energetic and alert?
(A) Those who voluntarily chose to take more
than 2 capsules daily reported energy levels
even greater than those who took only 2
capsules.
(B) The volunteers were randomly selected from
all those who answered a newspaper advertisement
and were willing to pay for the cost
of the Vita-Plus capsules.
(C) At the beginning of the study, the volunteers'
reports on alertness showed levels on average
no different from the average level reported
by the National Institutes of Health.
(D) Some of the volunteers were given capsules
that solely contained cellulose, an inert
substance with no vitamins or other healthinducing
substances. Those volunteers also
reported increased levels of alertness and
energy.
(E) Some of the volunteers were given capsules
that solely contained cellulose, an inert
substance with no vitamins or other healthinducing
substances. Those volunteers
reported no increase in alertness or energy.

D,E) out of scope. capsules containing cellulose are not discussed.
C) As initially it didn't show any effect, it doesn't strengthen the argument
B) correct. This proves that study was unbiased. volunteers were randomly selected.
A) maybe those who took more than 2 capsules daily already had higher level.
IMO B

interesting.... i am assuming that you have understood the argument. but writing again since you have not written what you couldn't understand.

take vita plus ... and be more alert and energetic.
supporting evidence is studies using hundreds of volunteers that took 2 capsules a day and reported being more energetic and alert than average people (in one week)

A, B, D are irrelevant

C talks about alertness levels. hence compares levels at the starting and end.
some results could have been becoz of vita plus but without a control sample how would you compare that the raised levels were because of vita plus. there could have been other reasons too.
E: best , strengthens the conclusion since it gives a controls sample. In which its comparing results with people who were not told that these cap don't have the medicine and these people didn't report any increase, ruling out other factors which could have been responsible for this change.

thats right force5.

Force5:How did you rule out A.
And E talks about only cellulose capsules.The fact that cellulose capsules didnt help does not strengthen the argument that vita capsule help.Its not touching the argument.
A on the other hand compares the relative alertness of those people who take 2 capsules and more,thus stating that its consumption of vita that causes alertness.Kindly let me know where I am getting it wrong.
Thanks.

@dhonu121: In A, there is a comparison between greater than 2 and just 2. Even though the amount 2 is not explicitly stated, we need to strengthen the case that 2 works better than none in increasing energy levels. If 2 does not work as expected than comparison between greater than 2 and just 2 does not effectively strengthen the case that 2 works better than none. Hope, I was able to explain the point...quite sleepy now..

About E, it strengthens the argument by showing that if any placebo or anything like cellulose which might help increase energy levels or alertness is given then there is no increase in those levels, whereas Vita Plus shows an increase which is indirectly strengthening the Vita Plus argument.

Choosing and Eliminating C is an interesting one. C is a necessary condition for the argument and can be considered as an assumption but does not show that Vita Plus has caused an increase so is not sufficient to strenghten it.

I think answer E should make that comparison between one group who were given a placebo and the other group who were given vita plus. It could have been worded better