Choosing the right graph makes a school project easier to understand and more convincing. Different graphs answer different kinds of questions, such as comparing categories, showing change over time, or looking for a relationship between two variables. A clear graph helps your audience see the main pattern quickly.
A poor graph can hide important information or make the data look misleading.
Key Facts
- Use a bar graph to compare separate categories, such as favorite sports or test scores by class period.
- Use a line graph for data collected in time order, such as temperature each day or plant height each week.
- Use a scatter plot to look for a relationship between two numerical variables, such as study time and quiz score.
- Use a pie chart only for parts of one whole, where all slices add to 100%.
- Use a histogram to show the distribution of numerical data grouped into intervals, such as heights from 150 to 159 cm.
- Use a box plot to summarize spread with five values: minimum, Q1, median, Q3, and maximum.
Vocabulary
- Category
- A category is a group or label used to sort data, such as color, grade level, or type of pet.
- Variable
- A variable is something that can change or be measured, such as time, height, temperature, or score.
- Time series
- A time series is data recorded in order over time, often shown with a line graph.
- Correlation
- Correlation describes how two numerical variables tend to change together, but it does not prove that one causes the other.
- Distribution
- A distribution shows how often different values or ranges of values occur in a data set.
Common Mistakes to Avoid
- Using a pie chart for data that do not make one whole is wrong because the slices should represent parts of a total that adds to 100%.
- Using a line graph for unordered categories is wrong because connecting the points suggests a continuous change that does not exist.
- Starting a bar graph axis at a misleading value without making it clear is wrong because it can exaggerate or shrink differences between categories.
- Using a scatter plot with only one numerical variable is wrong because scatter plots need paired values, one on each axis, to show a relationship.
Practice Questions
- 1 A student surveyed 80 classmates about their favorite lunch option: pizza 30, salad 10, tacos 25, sandwiches 15. Which graph should they use to compare the four lunch options, and what should the x-axis show?
- 2 A plant grew from 4 cm to 7 cm to 11 cm to 16 cm over four weeks. Which graph should show this change over time, and what ordered pairs would be plotted?
- 3 A student has data for hours studied and test scores for 20 classmates. They notice that higher study times usually go with higher scores. Which graph should they choose, and why would this graph be better than a pie chart?