4.18. Survey on Insurance and Freight Costs for Import Trade. The Census and Statistics Department of China, Hong Kong SAR, has been compiling a set of import statistics valued on a free on board (FOB) basis to facilitate analysis of the merchandise trade balance and comparison of trade statistics with those of other economies. The imports FOB valuation was derived from the imports CIF valuation based on data obtained from the Survey on Insurance and Freight Costs for Import Trade (IMS), which is a sample survey conducted since 1996 on a monthly basis. The main objective of IMS is to collect information on the insurance premium and freight cost incurred for imports of goods. Under the current sample design, trade items in import declarations are stratified by two variables, namely, Harmonized System (HS) section and mode of transport. Within each stratum, a proportionate random sample is drawn from the monthly import declarations, with the selection probability of each element proportional to its trade value. The total sample size determined on the basis of desired precision and resources availability is about 3,000 trade items per quarter. Data are collected by contacting the trader or company listed on the import declaration using the computer-assisted telephone interviewing (CATI) approach. Various measures, such as implementation of validation checks in the CATI system, online monitoring on the performance of individual field officers and verification of a sample of the enumerated cases by field supervisors, are adopted to safeguard the quality of the collected data.