Data-driven approaches for assessing robustness to uncertainty are gaining popularity as systems become more complex and harder to model accurately. This letter proposes a robustness analysis method using the integral quadratic constraint (IQC) framework. It is developed for linear parameter-varying (LPV) systems using time-domain IQCs. These time-domain IQCs are formulated directly using measured input-output data from the uncertainty. With one optimisation in the form of a semi-definite program (SDP), the optimal performance with respect to measured input-output behaviour of the uncertainty is determined, as well as the corresponding optimal IQC multiplier.