Introduction
Command of Evidence questions make up part of the Information and Ideas domain, which accounts for roughly 26% of SAT Reading and Writing operational questions. Within this domain, one category presents an informational graphic — a table, bar graph, or line graph — and asks you to identify which data point, comparison, or trend supports, challenges, or completes a claim in an accompanying passage.
Before you can evaluate any claim, you must read the graphic accurately. That reading step is exactly what this note trains. (How you then match that data to a claim — supporting, challenging, or completing it — is covered in the sibling notes Strengthening and Weakening a Hypothesis and Choosing Data That Completes the Claim.)
Core Concept
Every graphic on the SAT carries three layers of meaning you must extract before answering:
- What is being measured? (the variable or category on each axis / column header)
- What are the specific values? (the number attached to a bar, data point, or cell)
- What is the overall trend or pattern? (increasing, decreasing, no clear trend, one category outpacing another, etc.)
Misreading any one of these three layers is the root cause of nearly every wrong answer on graphic-based questions. The SAT designs distractors that use real numbers from the graphic but pair them with the wrong category, the wrong direction of change, or the wrong comparison group.
Reading a Table
A table organizes data in rows (one variable, often categories or groups) and columns (another variable, often a measurement or time period). Each cell is the intersection of exactly one row value and one column value. The most common errors: reading the wrong row, reading the wrong column, or misidentifying which variable is the row and which is the column.
Reading a Bar Graph
Each bar represents one category, and its height (or length for horizontal bars) encodes the value. Always check the scale: does the y-axis start at zero? A compressed scale makes small differences look dramatic. Compare bars by their heights, not by rough visual impression alone.
Reading a Line Graph
A line graph shows change over a continuous variable — usually time. The line's slope tells you direction (rising = increasing, falling = decreasing, flat = no change). When multiple lines appear, each line is a separate series (category or group); you must track which line belongs to which label before comparing them.
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