His first major line of research within this tradition concerns the phenomenon of empathic accuracy ("everyday mind reading").

[1] His second major line of research concerns the influence of personal traits and characteristics on people's initial interactions with each other.

His primary research advisor was Robert Wicklund, although Elliot Aronson was also an important professional mentor during this time.

His research has helped to answer several important questions about “everyday mind reading.” Do women display greater empathic accuracy than men?

The answer is that when all of these sources of information are available, our empathic accuracy generally depends most on what other people say, next-most on their paralinguistic cues (the pitch, inflection, and amplitude of their voice, for example), and least on their nonverbal behaviors.

The phenomenon of motivated inaccuracy that was introduced in the model has been substantiated in a number of studies[15][16] and has been linked to both avoidant and anxious-ambivalent attachment styles.

[17][18] In another important and long-term collaboration, William Ickes was involved in the series of studies that Lesley Verhofstadt and her Belgian colleagues conducted on the role of empathic accuracy in the social support displayed by married couples.

In addition to his work on empathic accuracy, Ickes has made a broader contribution to the study of intersubjective social cognition.

Subsequent papers[33][34][35] have elaborated this distinction, which owes much to the existentialist influence of writers such as Alfred Schütz and Maurice Merleau-Ponty.

In more recent research, Ickes and his colleagues have studied how latent semantic similarity (LSS) develops in dyadic interactions.

[46][47][48] More recently, he and his colleagues have developed other measures to assess the constructs of thin-skinned ego-defensiveness, affect intensity for anger and frustration, and rudeness.

[49][50][51] They have also published psychometric articles on (a) the pitfalls of using item variance as a measure of "traitedness"[52][53] and (b) the reduction in internal consistency that results from inter-item "context switching.