Descriptive Statistics - Data

Data

Data are very important for scientific study, and statistics is a discipline that deals with the collection, presentation and analysis of data. In this chapter we are going to study how we can summarize and describe a set of data. When we study a set of data we need to identify the following important characteristics of the dataset.

• Primary and secondary data. When the data are collected by us it is called primary data. We always have the individual values of the data. When the dataset is collected by others, it is called secondary data. Sometimes the data is grouped into a table, and is called grouped data.

• Population and sample data. Population refers to the totality of elements in which we are interested. Suppose we want to study the salary of Hong Kong people, our population includes all those persons who work in Hong Kong. However as the population is so big that it is not practical and economical to collect salary data of all the working people, we always select randomly only a subset of the population and the data is sample.

• Discrete and continuous data. It is important to identify whether the data is continuous or discrete. For example data on the number of persons in a household is discrete, and data on salary is continuous. Different statistical techniques are used for handling discrete or continuous data.