The impact of acquiescence bias in online samples is real and deserves serious research attention. This paper assesses the impact of acquiescence bias of online respondents on research output. Specifically, this paper addresses one type of acquiescence bias being increasingly observed in online panel rating scale data, where respondents exhibit low variability across rating scale items. This type of acquiescence bias is defined as flat line response bias in this study. The insidious effects of flat line response bias will be demonstrated on market segmentation and structural equation modelling in the context of a brand equity framework. This paper urges the market research industry to improve online recruitment and management to reduce flat line response bias in online panel surveys
