You observe that the distribution of weights of individuals drawn from a random sample of the United States appears bimodal; there are peaks at 130 lbs. and 165 lbs. You were under the impression that weights follow a normal distribution. Why do you think this distribution differs so much?

The sample is not representative of the population.

Individuals' weights better fit a uniform distribution.

The standard deviation of weights is greater than the mean weight.

The sample is comprised of males and females.

None of the above

Question

You observe that the distribution of weights of individuals drawn from a random sample of the United States appears bimodal; there are peaks at 130 lbs. and 165 lbs. You were under the impression that weights follow a normal distribution. Why do you think this distribution differs so much?

       The sample is not representative of the population.

       Individuals' weights better fit a uniform distribution.

       The standard deviation of weights is greater than the mean weight.

       The sample is comprised of males and females.

       None of the above

anonymous · Answer

@perl

perl · Answer

think about this logically, what would cause your distribution to have two bumps

anonymous · Answer

2 different samples

perl · Answer

your population is not as homogenous as you thought

anonymous · Answer

2 samples means 2 modes

perl · Answer

we are looking at one sample

perl · Answer

lets say its a big sample, 300 adult americans (where you define adult age)

anonymous · Answer

b

perl · Answer

over 18

anonymous · Answer

a uniform distribution is not a normal distribution

perl · Answer

thats true, but thats not relevant here

perl · Answer

when my draw button works, maybe i can graph it. but its basically two bumps

anonymous · Answer

The standard deviation of weights is greater than the mean weight.

anonymous · Answer

I still think a uniform ditribution is more relavent

anonymous · Answer

because it specifically says a standard distribution

anonymous · Answer

that is quite a contrast

tkhunny · Answer

"Two different samples" is no good.
"Two different distributions" is what you should be thinking about.

anonymous · Answer

a. the sample is not representative of the population

anonymous · Answer

there would be an inconsistent missing part of the puzzle not stated in the prompt which would indicate the theory of 2 possible different distributions.  Which would not be a normal distribution

tkhunny · Answer

Nah, Uniform is non-modal or poly-modal (infinitely many modes)

The only thing missing from the problem statement is the empirical knowledge that weights of the US population ARE Bi-Modal.  Why is this so?

anonymous · Answer

because the standard deviation of weights is greater than the mean weight

tkhunny · Answer

??  Males are generally larger than females.  You SHOULD find two modes in such a sample.

anonymous · Answer

does that mean there is a distribution for men and one for women as well

tkhunny · Answer

Yup.  And you just sampled from both of them - perhaps unwittingly.

anonymous · Answer

Perhaps..