The results are not a random sample of the vehicles on the road at all.
The results are for a random sample, and so any given child may show few or none of the problems.
Health officials say the reason such a study hasn't been done is the difficulty in getting a true random sample.
The study took a random sample of 1,600 households last July.
The control group was a random sample drawn from the general population.
For example, it may be impossible to use a random sample.
As an example, consider a random sample of size 6.
Thus the poll was not a random sample of Americans.
And that hour's data are not likely to represent a random sample of the public.
So it does not appear to be a random sample.
Wörterbuch für statistische Begriffe