respresentative sample?

Question

explain the meaning of this term, details of this sample

Answer 1

A representative sample should have the same characteristics of the population from which it is drawn. For example, if you wanted to find out the average height of all Americans, a sample that included mostly basketball players would NOT be representative, nor would a sample that included only women. Instead, a representative sample would include people of various races, both sexes, and all ages--so it would have the same variety of heights that can be found in the whole population.

Statistical theory says that the type of sample most likely to be representative is a random sample, a sample where random numbers or games of chance assure that every member in the population has an equal chance of being selected. Since this is often impractical to do, other types of "good" (usually representative) samples include systematic samples (where you number off and, for instance, call every 100th name in the phone book) and stratified samples (where you carefully include various sub-groups, like people of all different races in your sample).

Among the least representative samples are internet polls, where anyone who wants to can answer. Usually only those with strong opinions on a subject bother responding to such polls.

Answer 2

When trying to gather information, it is generally easier to ask / measure a sample of your target audience than to ask/ measure every one. However for this to work, the sample should be representative of the group as a whole.

E.g at election times, the media are all desperately trying to predict how the election is going to go, obviously they don't ask everyone who can vote, so they have to ask a sample of the population as a whole. For their polls to have any meaning, the sample of people they do ask, must try to represent the population as a whole. This means asking, men, women, rich, poor, employed, unemployed, black, white, English, Irish, Scottish, Welsh, etc. And all combination thereof. I'm sure you can see why representative samples are seldom truly representative.

As a rule of thumb, the smaller the sample in comparison to the actual size of people/ opinions/ things you are trying to sample, the less it truly represents that which you are sampling.

As for 'details of this sample' this would be specific to each example.

E.g if you are trying to determine the average of how many people are usually in a car, you could stand at a junction and count people in cars as they go by. However if you stand near a school, the numbers will be significantly different depending on whether your junction is on the way to school or the way back (mum has dropped off or picked up little Johnny)

If you are trying to find the average weight of an apple, you could weigh 6 of them and take the average, weighing 12 would be more representative, weighing 50,000 would be really representative (though costly to carry out). Your sample would only be valid for the type(s) of apple you weigh. I'm sure the average weight for a bramley is different to that of a golden delicious.

Answer 3

If you are learning statistics, sampling is a way of predicting the behaviour of a whole population from a sample. A representative sample should have the same proportions of different classes as the total population. In this way, the sample "represents" the whole population.

Answer 4

A representative sample, is polling the views, opinions, etc, of a sample of the population, ethnic, group, catchment area... It should be wholly representative of that field, including equal and fairly based selections of subjects. Most consider a representative sample to be pretty much impossible to obtain.

Answer 5

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Answer 6

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