Sampling is used in statistics because you can't possibly ask everyone in the world how old they are in order to find out the average age of all humans. But by getting a representative sample, you can make a pretty accurate estimation of the average age of everyone on the planet.
Another less obvious reason sampling is used is to get rid of bias. If you ask 10 of your friends if they like apples and 9 of them say they do, you can't say that 90% of people like apples. Maybe 90% of your friends, but it's very important to get a sample that accurately represents and reflects the population you are studying.
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Samples are used to describe the popularion (hence the name descriptive statistics). To perform a census or obtain data from a population is usually time consuming and costly.
A point estimate is a single value (statistic) used to estimate a population value (parameter)true apex
Statistic
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The test statistic is a measure of how close the sample proportion is to the null value.
Both are parametric test. The t-test uses a test statistic that is related to the sample mean(s) and is used to compare that with the mean of another sample or some population. The F-test uses a test statistic that is related to the sample variance and is used to compare that with the variance of another sample or some population. Both tests require identical independently distributed random variables. This ensures that the relevant test statistics are approximately normally distributed.