Interpreting data on ACT Science: a complete guide to reading graphs, tables, scatter plots, trends, interpolation, and units

Why Interpretation of Data carries the most points

Interpretation of Data is the largest of the three ACT Science reporting categories, so reading figures well is where most of your score is won. This guide ties together the matching dot-point pages, each with its own practice: reading line graphs and trends, reading tables and multi-variable data, interpolation and extrapolation, reading scatter plots and best-fit lines, and combining figures and reading units.

Line graphs: axes first, then value, then trend

The most common task is reading a line graph. The routine never changes.

1. Check the axes and units. Which variable is on the x-axis, which on the y-axis, and how are the gridlines spaced.
2. Read a value. Go up from the x-value to the curve, across to the y-axis.
3. Name a trend. Direct (y rises as x rises), inverse (y falls as x rises), or none (y flat), for the range the question names.

On a multi-line graph, read the legend and use the correct line for the condition asked.

Tables: orient, look up, isolate

Dense tables reward discipline.

• Orient: read the title, column headers, row labels, and units.
• Look up a value: find the right row (condition) and column (quantity), read the intersection; find the right block first if the table is blocked.
• Find a trend: read down a single column as the row variable changes.
• Isolate one variable: compare rows that differ in only that variable, holding the rest fixed.

Interpolation and extrapolation

• Interpolation estimates between known points along the trend. For a steady trend, a midpoint value is about the average of the two neighbours.
• Extrapolation predicts beyond the data by continuing the pattern. It is less certain, because real trends often level off or reverse outside the measured range.

Scatter plots and best-fit lines

A scatter plot shows individual points. Describe its correlation in two words.

• Direction: positive (rises to the right), negative (falls to the right), or none.
• Strength: strong (tight cluster) or weak (loose spread).

A line of best fit runs through the middle of the cloud; read it like any line to estimate values, and watch for outliers that sit far from the trend. Crucially, correlation does not prove causation: a third factor or coincidence can make two variables move together.

Combining figures and reading units

Some questions link two figures through a shared variable: read the shared value in one figure, carry it to the other. Throughout, guard the units and scale:

• Units: convert when a figure (mg/L) and the answers (g/L) differ.
• Scale spacing: count whether gridlines jump by 1, 5, 10, or 50.
• Axis breaks: a non-zero start or a break exaggerates small differences.

How this skill is examined

• Read a value at a point on a graph or at a table intersection.
• Name a trend (direct, inverse, none) over a stated range.
• Estimate by interpolation between points, or predict by extrapolation beyond them.
• Describe a scatter plot's correlation and read its best-fit line, without assuming causation.
• Bridge two figures through a shared variable and convert units to match the answers.

Check your knowledge

A quick check on the data-reading skills. Answer them, then read the solutions.

1. State the two-step path for reading the y-value at a given x-value on a line graph. (2 points)
2. A table varies both temperature and pH. To test temperature's effect alone, which rows do you compare? (2 points)
3. A quantity is 10 at x = 2 and 20 at x = 4, rising steadily. Estimate it at x = 3, and say whether this is interpolation or extrapolation. (2 points)
4. A scatter plot's points fall to the right and cluster tightly. Describe the correlation in two words. (2 points)
5. A figure is labelled in mg/L and an answer choice is in g/L. A point reads 500 mg/L. Give the value in g/L. (2 points)