First impressions in software development effort estimation: Easy to create and difficult to neutralize

The four studies included in this paper examine the strength of the first impression in the estimation of work effort. The studied context is mainly one where the first impressions of software development effort is manipulated (biased) through comparisons with either much too low or too high reference effort values, e.g., by responding to a question from the client whether one believes that the effort will be less than 10 work-hours when the likely usage of effort typically would be in the range of 100-300 work-hours. Then, the software developers are exposed to a subsequent comparison with reference effort values in the opposite direction, e.g., by responding to a question from the client whether one believes that the effort would be less than 800 work-hours. The results from the four studies suggest a strong first impression effect, but also a noticeable effect from the subsequent comparisons. We also observe that the instruction to “forget” the first impression seems to have the opposite effect, i.e., it seems to increase the strength of the first impression. A practical implication of the results is that it is essential that software professionals ensure that their first impression of a project’s development effort is based on comparisons with representative reference values and objects. First impressions in software development seem to be easy to manipulate with misleading reference values and difficult to replace.