We propose a new measure for explaining information search and compare it to the Payne index (PI), thus far the most commonly used measure for information search in process-tracing studies. The systematicity index (SI) explains information search in terms of systematicity or the proportion of non-random search, i.e. search that is compensatory (alternative-wise) or noncompensatory (attribute-wise) corrected for chance. The PI, on the other hand, shows the proportion of compensatory and noncompensatory search ignoring random search. We predict that the SI will be higher in environments where information is visually well-organized compared to environments where it is disorganized. We test the SI in a discrete choice experiment with four within-subjects conditions (compensatory, noncompensatory, systematic, and unsystematic visual grouping) using eye-tracking technology. The results show a higher SI in the systematic compared to the unsystematic condition. The PI, however, is close to zero in both conditions. The compensatory and noncompensatory conditions show similar SI but differ on PI. Our experiment shows that the SI is useful for calculating the amount of systematic information search in process-tracing studies and can shed light on processes not captured by the PI.