Studies in laboratory settings report that software development effort estimates can be strongly affected by effort-irrelevant and misleading information. To increase our knowledge about the importance of these effects in field settings, we paid 46 outsourcing companies from various countries to estimate the required effort of the same five software development projects. The companies were allocated randomly to either the original requirement specification or a manipulated version of the original requirement specification. The manipulations were as follows: 1) reduced length of requirement specification with no change of content, 2) information about the low effort spent on the development of the old system to be replaced, 3) information about the client's unrealistic expectations about low cost, and 4) a restriction of a short development period with start up a few months ahead. We found that the effect sizes in the field settings were much smaller than those found for similar manipulations in laboratory settings. Our findings suggest that we should be careful about generalizing to field settings the effect sizes found in laboratory settings. While laboratory settings can be useful to demonstrate the existence of an effect and better understand it, field studies may be needed to study the size and importance of these effects.