Collecting data through mixed-modes is becoming an ever more popular and necessary part of survey design, impacting both cross-sectional and longitudinal data. While interest in the topic is longstanding, our knowledge of its effects on measurement quality in panel studies is limited. The present paper will contribute to this debate by analyzing the impact of mixed modes of data collection on reliability in the Innovation Panel. This is a subsample of Understanding Society, a household panel survey representative of the UK population, that carries out methodological experiments. The random assignment to mixed mode (CAPI versus two types of CATI) in the second wave will give the opportunity to see the impact of mode design on measurement quality in this wave and subsequent ones. To assess these effects I will estimate the reliability of a subset of items over four waves using quasi simplex models for the different mode designs. I will further explain the differences in reliability by modes through variable level characteristics such as question complexity, topic or level of measurement.