Final answer:
A study's population is the whole group of interest, while a sample is a part that is actually observed.
Study units are the individual elements or subjects from which the data are collected.
Sampling methods must be chosen carefully to ensure the sample represents the population effectively.
Step-by-step explanation:
In any study, the population refers to the entire group of individuals or instances about which we hope to learn. A sample is a subset of the population that is actually observed or analyzed to draw conclusions about the whole group. Study units are the individual elements of research, often people or objects, from which data are collected.
In one study, the goal is to understand the mean number of extracurricular activities in which high school students participate. The population would be all high school students, and the sample consists of the 100 high school students surveyed. Here, each student represents a study unit.
In another example, an insurance company aims to find out the proportion of medical doctors involved in malpractice lawsuits. The population is all medical doctors, and the sample is the 500 doctors chosen from a professional directory. Each doctor is a study unit.
To achieve representative results, the sample should accurately reflect the population. Different types of sampling techniques like simple random sampling, stratified sampling, or systematic sampling can be used. In an example, a soccer coach uses stratified sampling to form a team by selecting players from different age groups, ensuring that each stratum (age group) is represented.