Difference between Sample and Population

A population is the entire group of individuals about whom you want to draw conclusions. In contrast, a sample is the subset of the same entire group.

Example 1 of sample and population

You would like to study if students like online courses at your university. Suppose your university has 10K students; thus, these 10K students are the population.

If you randomly choose 200 students, out of the 10K students, these 200 students are the sample.

Illustration of Sample vs. population
Illustration of Sample vs. Population

Example 2 of sample and population

Suppose that a Math course has 11 students. If you want to see how these students perform in a Math exam, these 11 students are the population.

If you randomly select 5 of them to calculate the mean (instead of all 11 of them), these 5 students are the sample.

Difference and connection between population and sample
Difference and connection between population and sample

Why use samples, instead of populations?

A sample can be used to make inferences about the population. There are a few reasons we choose to use a sample rather than the whole population.

1. Save time

Surveying or measuring everyone in a population can be time-consuming. For instance, in the first example, if a researcher chooses to survey the whole population of all 10K students about their opinions, it will take a lot of time. Thus, sampling can help save researchers time by using a sample to infer the population.

2. Save money

Using a sample rather than the whole population in data collection can help save money in a lot of situations. It makes sense that the number of people/objects a researcher contacts/measures is directly related to the cost of a study. 

3. Unfeasible situations

Samples can help deal with situations where collecting data from the whole population is unfeasible or practically impossible. For instance, if a biologist wants to understand the average tree height in the Amazon forest, it would be unfeasible for the biologist to measure every tree in Amazon.

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