Types of Data and Sampling Methods

What is a variable?

A characteristic that can vary in value among subjects in a sample or a population

What is a quantitative variable?

It is when the measurement scale has numerical values

What is a categorical (qualitative) variable?

It is a type of variable that represents distinct groups used to classify data

What is a discrete variable?

A unit that cannot be subdivided. A finite number of possible values (or categories)

What is a continuous variable?

A variable that can take infinite possible numbers

What is a population?

The total set of subject of interest in a study

What is population parameters?

A numerical summary of the population

What is a sample?

A subset of the population on which a study collects data

What is a statistic?

A value taken from a single sample used to estimate a parameter

What is descriptive statistics?

A summary of the information in a collection of data using graphs, tables and numbers

What is inferential statistics?

It provides predictions about a population, based on data from a sample of that population

What is a sampling frame?

It is the list of all the people/objects in your population

What is a sampling fraction?

It is the proportion of the population being sampled

What is a census?

A 100% sampling fraction

How to calculate a sampling fraction?

Sample size / population

When you don’t have a sampling frame, what do you use?

Non-probability samples such as quota sample and convenience sample

When you have a sampling frame, what do you use?

Probability samples such as simple random sample, systematic sample, stratified sample and cluster sample

Method for simple random sampling:

• Allocate a number (ID) to each item in your sampling frame
• Select a number by using a random number function on your calculator or tables

What is the method for systematic sampling?

• Give number (ID) to each item/person in your sampling frame
• Calculate the interval by dividing the population size (N) by the sample size (n)
• Generate a random starting point using 1000 ran# =
• Select an item/person with that number
• Add the calculated interval to the starting point to get the next ID of employee. And so on

What is the method for stratified sampling

• Divide the population in your sampling frame into categories
• Divide the size of category by the total size of population and multiply by the sample size
• Select the sample for each category at random using simple random sampling