measurement of the sampling variability and is supported by the laws of 

 probability. Statistical sampling provides an objective method for 

 determining the sample size (for variables and for proportions), for 

 estimating population parameters for a desired confidence level and 

 precision, and for evaluating the cost tradeoffs based upon a desired 

 confidence level and precision. 



The proposed underwater inspection sampling criteria use statistical 

 sampling methods and inferences. From data collected during the field 

 validation tests of the sampling criteria at St. Helena and Naval Station, 

 Mayport, a minimum sample size of 30 elements has been shown to provide 

 adequate data for statistical inference for waterfront timber and steel 

 structures, in most cases with a confidence level of 95 percent (1 out 

 of 20 chance of being wrong) for the precision of measurement tools that 

 were used in the field tests, when a single attribute is chosen for 

 investigation (e.g., number of piles with marine borer activity), a 

 larger sample size is required. However, measurements are not normally 

 required since detection of borer activity is usually obtained by visual 

 inspection (unless core samples are used). In any case, the maximum 

 number of samples needed for a confidence level of 95 percent with an 

 accuracy of 10 percent, considering the worst case distribution of 

 50 percent, would be 97 samples. 



Based on the studies and validation inspections conducted during 

 this project, the following conclusions and recommendations are pre- 

 sented: 



The scientific approach to sampling, where an estimate of the con- 

 dition and the extent of required maintenance is obtained, guarantees 

 that the inspection will gather information that can be analyzed in a 

 manner consistent with standard statistical practices. The procedures 

 presented In this report yield results that can be relied upon for a 

 given confidence level and accuracy requirement. The criteria presented 

 in this report provide a scientific method for specifying the number of 

 elements to be sampled for each waterfront facility. Data obtained using 

 these criteria can be compared to each other with proven correlation 

 procedures to indicate trends in deterioration rates and allow more 

 accurate projections of maintenance and repair requirements. 



