Video streaming online services ranked by number of tablet users in the UK 2016

The source adds the following information on methodology:
"The Verto Analytics single-source measurement methodology is based on behavioural data gathered from a panel of consumers that own and use multiple devices. Our panelists, who are incentivized for their participation, opt in to install a measurement app on all of their digital devices. Simply put, we quantify the consumer journey across all apps, sites, services, and devices. We calibrate the panel data against our census-level crossdevice calibration data."