What type of test design technique uses values at the edge of input ranges?

The technique that specifically focuses on values at the edge of input ranges is boundary value analysis. This approach is grounded in the observation that errors often occur at the boundaries of input ranges rather than within the ranges themselves. For example, if a certain input value is valid within a defined range (like from 10 to 20), boundary value analysis would test values such as 9, 10, 20, and 21.

By concentrating on these boundary points, testers can more efficiently identify potential defects that might not be uncovered through other testing methods. This technique is particularly valuable for ensuring that software behaves correctly at the extremes of input ranges, where validation and boundary-checking are critical.

Equivalence partitioning, on the other hand, divides input data into valid and invalid partitions to minimize the number of test cases while still providing sufficient coverage. State transition testing and decision table testing focus on modelling the system's responses based on different states or decision combinations, rather than specifically on boundary values. Thus, the distinctive focus of boundary value analysis on edge cases solidifies its role as the correct answer in this context.