Frequency — Definition, Formula & Examples
Frequency is the number of times a particular value or category appears in a data set. If five students scored 90 on a test, the frequency of the score 90 is 5.
In statistics, the frequency of a data value is the count of observations in a data set that are equal to that value. For categorical data, it is the count of observations belonging to a given category.
How It Works
To find frequencies, list every distinct value or category in your data set, then count how many times each one occurs. You can organize these counts in a frequency table, where one column lists the values and another lists their frequencies. The sum of all frequencies must equal the total number of data points. Frequencies are the foundation for building bar graphs, histograms, and dot plots.
Worked Example
Problem: A teacher records the favorite colors of 12 students: Red, Blue, Green, Blue, Red, Blue, Green, Red, Red, Blue, Green, Blue. Find the frequency of each color.
Count Red: Go through the list and count every occurrence of Red.
Count Blue: Count every occurrence of Blue.
Count Green: Count every occurrence of Green.
Answer: Red: 4, Blue: 5, Green: 3. The frequencies add up to 12, confirming every data point is accounted for.
Visualization
Why It Matters
Frequency is the first step in nearly every data analysis task you will encounter, from summarizing survey results to constructing graphs. In science classes, you record experimental outcomes as frequencies before drawing any conclusions. Understanding frequency also prepares you for relative frequency and probability in later courses.
Common Mistakes
Mistake: Confusing frequency with relative frequency.
Correction: Frequency is a raw count (e.g., 5), while relative frequency is that count divided by the total number of data points (e.g., 5 out of 20 = 0.25). Always check whether a problem asks for a count or a proportion.