2007-02-19 01:15:23 · 8 answers · asked by Mighitman 3 in Environment
Because an entire population would be much more time consuming and you can get an pretty accurate survey from a sample. Imagine trying to sample everyone in the US, how long would that take, how many people wouldn't do it, etc.
2007-02-19 01:18:55 · answer #1 · answered by leo 6 · 0⤊ 0⤋
The sample is a means to an end. The sample (n) is tested to be a representative of the entire population. When you collect data on continuous traits you test normality. A normal distribution in your data would look like the bell curve. If the data does not deviate significantly from normality then it is deemed that the sample is representative of the population, i.e, random sampling.
If the bell curve is skewed in a direction and is not normal then you have biased sampling and your data does not represent the population. Basically what the other guys said. Its a cost effective, time saver which is reasonably reliable to obtain a representative sample of the population.
2007-02-19 09:23:20 · answer #2 · answered by Gord 2 · 0⤊ 0⤋
Depends on the size on the population. If you wanted data on all the oak trees in your yard, you would not need a sample. If you wanted data on all the oaks in the Shawnee National Forest you'd need a sample. It would just be too costly and time consuming to go out there a measure every oak tree.
There are methods for sampling also. Someone conducting the sampling would want to find what's called a representative sample. There would be desired parameters within the sample. Like for oak trees. Maybe they would want to sample one species. Perhaps sample trees of a particular size.
I would suggest you take a basic statistics course.
2007-02-19 09:36:11 · answer #3 · answered by Anonymous · 0⤊ 0⤋
Because it's not cost effective to collect data from the entire (billions) population.
2007-02-19 09:17:53 · answer #4 · answered by jacksfullhouse 5 · 0⤊ 0⤋
Logistical necessity. Most populationns (human and other life forms) number in the millions, or more. Collecting data from all members of the population isn't practical--if not downright impossible.
2007-02-19 09:33:52 · answer #5 · answered by Anonymous · 0⤊ 0⤋
It takes too much time and effort to poll an entire population. Extracting from a sizable sample is statistically "good enough."
2007-02-19 09:18:29 · answer #6 · answered by Vegan 7 · 1⤊ 0⤋
Because it is impractical $ us to collect data fropm a large popuklation. Always a smaller one, can act as a model of a bigger population.
Just to make it easier
2007-02-19 09:18:48 · answer #7 · answered by malu 2 · 0⤊ 0⤋
Have you ever tried to get 6 billion people to answer a questionaire?
2007-02-19 09:17:47 · answer #8 · answered by rip snort 3 · 1⤊ 0⤋