  CONTEXT: The role of expert judgement is essential in our quest to improve
software project planning and execution. However, its accuracy is dependent on
many factors, not least the avoidance of judgement biases, such as the
anchoring bias, arising from being influenced by initial information, even when
it's misleading or irrelevant. This strong effect is widely documented.
OBJECTIVE: We aimed to replicate this anchoring bias using professionals and,
novel in a software engineering context, explore de-biasing interventions
through increasing knowledge and awareness of judgement biases. METHOD: We ran
two series of experiments in company settings with a total of 410 software
developers. Some developers took part in a workshop to heighten their awareness
of a range of cognitive biases, including anchoring. Later, the anchoring bias
was induced by presenting low or high productivity values, followed by the
participants' estimates of their own project productivity. Our hypothesis was
that the workshop would lead to reduced bias, i.e., work as a de-biasing
intervention. RESULTS: The anchors had a large effect (robust Cohen's $d=1.19$)
in influencing estimates. This was substantially reduced in those participants
who attended the workshop (robust Cohen's $d=0.72$). The reduced bias related
mainly to the high anchor. The de-biasing intervention also led to a threefold
reduction in estimate variance. CONCLUSIONS: The impact of anchors upon
judgement was substantial. Learning about judgement biases does appear capable
of mitigating, although not removing, the anchoring bias. The positive effect
of de-biasing through learning about biases suggests that it has value.
