837. This chapter and the one that follows are primarily concerned with the development of an ITRS or of ES to collect BOP data. This chapter focuses on principles of survey (or collection) design, and chapter 19 deals with form design. However, collections for several other types of data sources—official sources, households, and ITS—are not discussed. While surveys to obtain data from official sources could be designed on the basis of principles described in these two chapters, the development of collection methodology for the official sector is not normally complex. Collections of household data and of ITS, both of which are used by BOP compilers, are typically undertaken by other compilers.