What is data?
Data is a collection of facts, numbers or observations. We collect data to answer a question, for example "Which drink is most popular in class?". Data can be collected through interviews, questionnaires, observation or experiments. Once collected, raw data is messy, so we organise it, represent it with a chart, and then interpret it to draw conclusions.
Organising data
A frequency table counts how many times each value appears. We use tally marks in groups of five (llll crossed out = 5) to count quickly, then write the frequency as a number.
Key idea / Key idea
Frequency = how many times a value occurs. The total frequency equals the total number of data items collected.
Representing data
We can show data with a pictograph (pictures, each equal to a fixed amount), a bar chart (bars whose heights show frequency), a pie chart (a circle split into sectors) or a line graph (points joined to show change over time). The right chart depends on what you want to compare.
Worked example
30 pupils chose a favourite fruit: Apple 12, Banana 9, Orange 6, Grape 3. Draw a bar chart with fruit on the horizontal axis and frequency on the vertical axis. The Apple bar is tallest at 12; the Grape bar is shortest at 3. Check: 12 + 9 + 6 + 3 = 30, matching the number of pupils.
For a pictograph using 1 picture = 3 pupils, Apple needs 12 ÷ 3 = 4 pictures and Grape needs 3 ÷ 3 = 1 picture.
Interpreting data
Interpreting means reading the chart to answer questions: which is the largest, the smallest, the difference between two values, or the total. Always read the scale carefully before answering.
Remember
- Every bar chart and graph needs a title and labelled axes.
- The sum of all frequencies = total data collected.
- In a pictograph always state the key (1 picture = how many).