What is the minimum number of units assessed in a random sampling of a building built before 1960?

The correct answer regarding the minimum number of units assessed in a random sampling of a building built before 1960 is based on established guidelines set forth for lead risk assessments. In this context, assessing at least 20 units ensures an adequate representation of the variability and conditions present in the building. This number provides a reliable dataset for evaluating potential lead hazards, considering the various construction methods and painting practices that may have been used in different areas of the building.

When a building has a common construction and painting history, the sampling size can focus on 20 units, which is sufficient for a robust statistical analysis. It balances the need for thoroughness against practical constraints like time and resources.

Larger sampling sizes, such as 25 or more, may indeed offer even more reliability and detail, but the standards set for lead risk assessment specify a minimum of 20 units under the conditions provided. Lower numbers, such as 10 or 15, would not adequately capture the necessary variability in lead-related conditions and could result in misleading conclusions regarding lead risks present in the building. Therefore, selecting 20 units is essential for an effective assessment that fully considers the historical context and potential risks associated with lead exposure.