Workload Does Not Work: On the Many Problems of the NASA-TLX

The NASA-Task Load Index (TLX) and its variants are the most widely used measures of mental workload. However, an increasing body of literature suggests that there are critical problems with this measure. This includes confusing elements of its design that may bias human response or result in administrator error, inconsistent dimensions, limitations in how dimensions are weighted when computing overall workload scores, multicollinearity between dimensions biasing results, and fundamental measurement theory problems that impact the meaningfulness of computed overall workload. This article provides an overview of these problems. We then make recommendations for addressing them through changes in experimental practice and design, as well as practices that can be used by researchers in the intervening period. We recommend that researchers assess the appropriateness of the TLX for every study, combine its use with other measures, analyze dimensions separately instead of overall workload, and use within-subject designs when possible. Finally, we call on the research community to standardize NASA-TLX versions and instructions, audit existing TLX results, and investigate methods to address existential issues.