Critical Reasoning

Source: Manhattan GMAT CR Guide 4th Ed

In a recent poll, 71% of respondents reported that they cast votes in the most recent national election. Voting records show, however, that only 60% of eligible voters actually voted in that election.

Which of the following pieces of evidence, if true, would provide the best explanation for the discrepancy?

A: The margin of error for the survey was plus or minus five percentage pints. => INCORRECT
B: Fifteen percent of the survey's respondents were living overseas at the time of election. => INCORRECT
C: Prior research has shown that people who actually do vote are also more likely to respond to polls than those who do not vote.
D: Some people who intended to vote are presented from doing so by last minute conflicts on election day or other complications.
E: Polls about voting behavior typically have margins of error within plus or minus three percentage points. => INCORRECT

OA: C

What about C and D?

60% of the eligible voters means voters who actually cast their vote,while 71% respondents can be people who were eligible to vote or people who were not eligible to vote.

C is straight away answer.

D is a behavior that people generally so.
But here both the events are already happened so the behavior doesn't matter.

Just be careful :

CAST : past event

Let me break this up....
suppose in a area 1000 ppl lived who were eligible to vote....
poll result shows 60% success... which means 600 ppl actually voted....

Now, the survey result-
71% said 'yes'.... the survey may have covered only 500 ppl or lets say the survey was responded by only 500 ppl who were excited about the election, though some of them would not have been able to vote...rest 500(including some of the ppl who actually voted) did not bother to answer the survey....

out of the 500 survey respondents, the number of ppl actually voted would be 355, rest would not have voted or were not eligible to vote...The agency which conducted the survey speculated and presented to the public that 71% voting has been done...

Hence, choice C fits the best...

Agree with Paes here

D: Some people who intended to vote are presented from doing so by last minute conflicts on election day or other complications. ... So , if 10 people decided to vote ... 5 people actually voted and 4 people responded to the survey.. Here we are not talking about the 10 people .... The are talking about the 2 groups colored in red... Example - So 5/10 = 50% and 4/5 = 80%.... Similar percentages have been furnished in the question stem

1. The survey happened after the vote. So no need to care for reason why people could not vote.

2. This is percentage problem:
71% of respondents (70% of X)
60% of actual vote (60% of Y) is eligible
Since X&Y is basically different from each other, no comparison should be made here
why these 2 numbers are different?

Answer C: In total number of respondents: actual voters are more likely to participate in survey --> percentage of actual voters is higher than those not voting ---> that's why it is 71%

Only Answer C helps to clarify why the 71% percentage is so high and this is not correlated with the 60%.
3. Other answers address out of scope explanation
4. C is best among these

IMO C.
As it shows that there might be discrepancy in both the values.