In the early stages of software development, inspection of software documents is the most effective quality assurance measure to detect defects and provides timely feedback on quality to developers and managers. This paper reports on a controlled experiment that investigates the effect of defect detection techniques on software product and inspection process quality. The experiment compares defect detection effectiveness and efficiency of a general reading technique, that uses checklist-based reading, and a systematic reading technique, scenario-based reading, for requirements documents. On the individual level effectiveness was found to be higher for the general reading technique, while the focus of the systematic reading technique lead to a higher yield of severe defects compared to the general reading technique. On group level, which combined inspectors' contributions, the advantage of a reading technique regarding defect detection effectiveness depended on the size of the group, while the systematic reading technique generally exhibited better defect detection efficiency.