CFA Practice Question

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CFA Practice Question

Which of the following samples would best represent the associated populations?

A. lifetimes of 300 randomly chosen 100-watt bulbs; lifetimes of all 100-watt bulbs
B. body weights of 20 randomly picked NFL kickers; body weights of all NFL players
C. salaries of 750 randomly selected Boston doctors; salaries of all Boston employees
D. number of yearly lightning storms in Florida; number of yearly lightning storms in U. S.
Correct Answer: A

User Contributed Comments 12

User Comment
sdutt2475 What is associated population ?
zlpp all 100-watt bulbs
Carter Consider it this way:

Does it really make any sense to measure kickers when we want information about all players (kickers, quarterbacks, defensive ends, etc)? No. All NFL players are not going to represented by sampling kickers. (That's why they're kickers instead of another position.)

Same idea on C. The salary of Boston Doctors do not reflect the salary of all employees in Boston. I'm sure this would be true in all cities unless you can find a city that is comprised of only doctors.

When we have an associated population, it means that our sample is related to (and preferable representative of) the population we are learning about.
surob I didn't understand why D is not the right answer. I agree A is the right one too, but thought D would work too. Any thoughts
Indira Florida does not represent all US states, so the sample is not representative.
Bibhu Always sample should be representative of population. So choice of D is wrong. Most importantly when we talk about weather, we should take little bit more time in analyzing whether the sample is representative of population. It sometimes misleads.
childpsych1 I also thought D was the right answer because Florida is one of the states of US but yes on deep thought it does not represent all the states - this was a truly tricky question
sam95 I disagree as well as A you can say that it is the best described sample. But even D is correct because if Florida is randomly selected from US and the no of lightening in it will be taken as a sample.Probably the trick in this is, they did not mention that Florida is "RANDOMLY" selected
Meka76 I agree with sam95 - I believe the reason that D is not correct is that Florida was not "randomly" selected. For it to be correct, we need to know that all the other states had an equal opportunity of being chosen which is not indicated in the wording.
Laurier Remember, the question is asking about which sample is "best" representative of its associated population. I'm not sure that randomness has much to do with it. Try flipping the question:

Is there an inherent reason why kickers may NOT be representative of all NFL players when it comes to weight? (Sure, the physique they need is much different than that of a D-line player)

Is there an inherent reason why Florida may NOT be representative of all states when in comes to lightning storms? (Sure, it's by the ocean, it's got a warm climate, right by the Gulf stream, etc.)

Is there an inherent reason why 300 light bulbs would not represent all bulbs of the same wattage when it comes to lifetime? (Um... the answer isn't quite as obvious as the others, so likely the "best" representative, which is what we're looking for)
Jordan2117 All of the light bulbs are uniform. States climates vary widely over the country florida accounts for a very small portion. Seattle rains more than Dallas- same concept I think the light bulb is clearly the best choice.
kingirm Bulbs-all bulbs...kickers -players... doctors-employees... in Florida-in the USA. .. only A is good
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