Introduction to Population and Sample
A population often consists of a large group of specifically defined elements. For example, the population of a specific country means all the people living within the boundaries of that country.
Usually, it is not possible or practical to measure data for every element of the population under study. We randomly select a small group of elements from the population and call it a sample. Inferences about the population are then made on the basis of several samples.
A company is thinking about buying 50,000 electric batteries from a manufacturer. It will buy the batteries if no more that 1% of the batteries are defective. It is not possible to test each battery in the population of 50,000 batteries since it takes time and costs money. Instead, it will select few samples of 500 batteries each and test them for defects. The results of these tests will then be used to estimate the percentage of defective batteries in the population.
Quantitative and Qualitative Data
Data is quantitative if the observations or measurements made on a given variable of a sample or population have numerical values.
Example: height, weight, number of children, blood pressure, current, voltage.
Data is qualitative if words, groups and categories represents the observations or measurements.
Example: colors, yes-no answers, blood group.
Quantitative data is discrete if the corresponding data values take discrete values and it is continuous if the data values take continuous values.
Example of discrete data: number of children, number of cars.
Example of continuous data: speed, distance, time, pressure.
More References and linkselementary statistics and probabilities.
Probability Questions with Solutions.