113 MBA students debugged a single model seeded with eight errors. Subjects either looked at the model on-screen or on paper. With the onscreen presentation, subjects caught fewer errors then they caught with paper presentations. Undergraduate MIS majors who had built a spreadsheet for the Wall task were given the opportunity to correct their errors. No subject with a correct model changed it.
Spreadsheet errors appear to be about as frequent as errors in programming.
Programming reliability requires an extensive testing phase that may include code inspection. A similar testing phase may be needed in spreadsheeting. We conducted an experiment using the full two-phase programming code inspection methodology. In addition, subjects had a minimum completion time for the individual and group inspections, to prevent hasty inspection. However groups did not find any new errors, and one group even lost an error found by one of its members in the individual phase.