Census — Definition, Formula & Examples
A census is the collection of data from every single member of a population. Instead of surveying just some people or items, a census gathers information from all of them.
A census is a complete enumeration of all individuals or elements in a defined population, in which every unit is observed or measured for the variable(s) of interest.
How It Works
To conduct a census, you first define the entire population you want to study. Then you collect data from every member of that population — no one is left out. Because every member is included, the results describe the population exactly rather than estimating it. Censuses are practical when the population is small, like a classroom, but become expensive and time-consuming for large populations, which is why samples are often used instead.
Worked Example
Problem: A teacher wants to know the average height of all 20 students in her class. She measures every student and records: 150, 152, 148, 155, 160, 145, 158, 153, 149, 157, 151, 154, 156, 147, 159, 146, 161, 150, 152, 155 (all in cm). Find the mean height.
Step 1: Confirm this is a census: data was collected from all 20 students, not a subset.
Step 2: Add all 20 heights together.
Step 3: Divide the total by the number of students to find the population mean.
Answer: The exact population mean height is 152.9 cm. Because this was a census, this value is the true mean — not an estimate.
Why It Matters
The U.S. Census, conducted every 10 years, determines how many representatives each state gets in Congress and how billions of dollars in federal funding are distributed. Understanding the difference between a census and a sample is essential for interpreting data correctly in statistics courses and in everyday news reports.
Common Mistakes
Mistake: Confusing a census with a sample.
Correction: A census collects data from every member of a population. A sample collects data from only a part of the population. If even one member is excluded, it is no longer a census.