GMAT Data Insights common mistakes
GMAT Data Insights · Understand the traps and how to avoid them.
Assuming a variable is positive
A sign assumption can remove valid cases and make insufficient information look sufficient.
What to do instead
List the stated domain and test permitted positive, negative or zero cases where they can change the requested answer.
Accepting one successful example
An example can fit a proposed rule without showing that all allowed cases have the same outcome.
What to do instead
Seek a permitted counterexample or explain why the algebra covers every value in the stated domain.
Mixing percent and percentage points
The difference between two rates and a relative change from a baseline use different denominators.
What to do instead
Write the requested comparison as a fraction or difference before computing, and label the resulting unit.
Losing a solution through division
Dividing by a variable expression silently assumes that expression is nonzero and can discard a valid case.
What to do instead
Factor or separate the zero case first, then check all candidates in the original relation.
Ignoring equivalent answers
Distinct-looking algebraic forms or unreduced fractions can represent the same value or solution set.
What to do instead
Simplify and compare every plausible option, checking original restrictions before accepting a unique key.
Averaging unequal group means directly
Groups with different counts contribute different numbers of observations to the combined total.
What to do instead
Recover each group sum from its count and mean, add the sums and divide by the combined count.
Treating correlation as a causal guarantee
A numerical association can arise through confounding, selection or chance without proving the proposed mechanism.
What to do instead
State the observed pattern and identify additional evidence or design needed for a causal conclusion.
Importing an unstated source fact
A familiar test format, historical belief or external example can contradict the actual supplied passage or model.
What to do instead
Use the question’s sources and restrictions first, and leave current exam policy and unsupported facts unspecified.