The introduction of iOS 13's app tracking alert has significantly reduced the flow of location data to the ad industry, making it harder for advertisers to track users. According to data from Location Sciences, approximately 80% of iPhone users who installed the update stopped all background tracking by apps. This change has impacted the ability of firms to measure the effectiveness of campaigns and has led to a reduction in advertiser spending. The quality of available location data has also decreased, with more data being sourced from lower-quality sources such as carriers or internet protocols.