Grade: Grade 6 Subject: Science Unit: Experimental Design Lesson: 4 of 6 SAT: ProblemSolving+DataAnalysis ACT: Science

Data and Graphs

Learn

After conducting an experiment, scientists must organize their data and present it in a way that helps them (and others) understand the results. This lesson covers how to create data tables, calculate averages, and choose the right type of graph.

Organizing Data in Tables

A data table is a structured way to record and organize observations. A well-designed data table includes:

  • A clear, descriptive title
  • Column headers with variable names and units
  • The independent variable in the first column
  • The dependent variable in subsequent columns
  • Space for multiple trials and averages

Calculating Averages (Mean)

When you conduct multiple trials, you need to calculate the average (or mean) to find the typical result:

Average = Sum of all values / Number of values

Example: If your plant heights are 12 cm, 14 cm, and 13 cm, the average is:

(12 + 14 + 13) / 3 = 39 / 3 = 13 cm

Types of Graphs

Different types of data require different graphs:

Bar Graphs

  • Best for categorical data (groups or categories)
  • Used when the independent variable is not numerical
  • Example: Comparing plant growth with different fertilizer brands

Line Graphs

  • Best for showing change over time or continuous data
  • Used when both variables are numerical
  • Shows trends and patterns
  • Example: Plant height measured each day over 2 weeks

Circle Graphs (Pie Charts)

  • Best for showing parts of a whole
  • All sections must add up to 100%
  • Example: Percentage of students who prefer different science topics

Creating a Proper Graph

Every scientific graph needs these elements:

  1. Title: Describes what the graph shows (often "Effect of [IV] on [DV]")
  2. X-axis label: Independent variable with units
  3. Y-axis label: Dependent variable with units
  4. Appropriate scale: Numbers evenly spaced, starting at zero when possible
  5. Plotted data points: Accurately placed on the graph
  6. Legend/Key: If showing multiple data sets

Interpreting Graphs

When analyzing a graph, ask yourself:

  • What is the overall trend? (increasing, decreasing, constant)
  • Are there any patterns?
  • Are there any outliers (data points that don't fit the pattern)?
  • What conclusions can you draw?

Examples

Work through these examples to practice organizing and graphing data.

Example 1: Creating a Data Table

Experiment: Testing how temperature affects dissolving time of sugar

Sample Data Table:

Effect of Water Temperature on Sugar Dissolving Time
Temperature (C) Trial 1 (sec) Trial 2 (sec) Trial 3 (sec) Average (sec)
20 45 48 42 45
40 28 30 29 29
60 15 18 15 16
80 8 9 7 8

Example 2: Choosing the Right Graph

Scenario A: You measured how many insects were found in 4 different habitats.

Best graph: Bar graph (comparing categories: forest, grassland, desert, wetland)

Scenario B: You recorded a plant's height every day for 14 days.

Best graph: Line graph (showing change over time)

Scenario C: You surveyed students about their favorite planet, and want to show what percent chose each planet.

Best graph: Circle/pie graph (showing parts of a whole)

Example 3: Interpreting a Line Graph

A line graph shows plant height over 10 days. The line goes up steeply from day 1-5, then levels off from day 5-10.

Interpretation: The plant grew rapidly during the first 5 days, then growth slowed significantly. This might indicate the plant reached its maximum height, ran out of nutrients, or became root-bound in its container.

Practice

Try these problems on your own to reinforce your learning.

1. Calculate the average of these trial results: 24, 28, 22, 26, 25

2. A student is comparing how fast different brands of paper towels absorb water. What type of graph should she use? Explain why.

3. What are the five essential elements every scientific graph must have?

4. A scientist collected this data on bacteria growth:
Hour 0: 100 bacteria
Hour 2: 200 bacteria
Hour 4: 400 bacteria
Hour 6: 800 bacteria
What type of graph would best show this data? What trend do you notice?

5. Design a data table for an experiment testing how the amount of light affects the number of bubbles produced by an aquatic plant. Include columns for 3 trials.

6. Why is it important to include units on graph axes?

7. A student's graph shows that as the amount of fertilizer increases from 0g to 50g, plant height increases. But at 75g and 100g of fertilizer, plant height decreases. What might explain this pattern?

8. What is an outlier? Give an example of when you might see one in experimental data.

9. A data table shows these trial results for how far a ball rolled: Trial 1: 45 cm, Trial 2: 44 cm, Trial 3: 89 cm, Trial 4: 46 cm. Calculate the average. Should you include all trials? Why or why not?

10. Explain the difference between when you would use a bar graph versus a line graph. Give a specific example of each.

Check Your Understanding

Test yourself with these review questions.

1. Which type of graph would be best to show how temperature changed throughout a 24-hour period?

  • A) Bar graph
  • B) Line graph
  • C) Circle graph
  • D) Pictograph

2. In a data table, where should the independent variable be placed?

  • A) In the title
  • B) In the first column
  • C) In the last column
  • D) In the average column

3. What is the average of the following data set: 10, 15, 20, 15?

  • A) 10
  • B) 15
  • C) 20
  • D) 60

4. On a graph, which axis typically shows the dependent variable?

  • A) X-axis (horizontal)
  • B) Y-axis (vertical)
  • C) Either axis
  • D) Neither axis

Next Steps

  • Practice creating data tables for experiments you read about
  • Look at graphs in news articles or textbooks and identify their key elements
  • Try graphing data by hand before using computer software
  • Move on to the next lesson: CER Writing