(2) If the analysis indicates a requirement for maintenance, 

 analyze the proportion of piles in each maintenance 

 category to assure that the attribute sampling criteria 

 can be satisfied. 



After collecting the data from the original sample, the mean and 

 standard deviation should be calculated. These values are then substi- 

 tuted into Equation 7 or 8 to determine the required sample size based 

 on the actual versus assumed condition of the structure. If the new 

 sample size requirement exceeds the original projection, then additional 

 random samples must be selected using the procedures outlined above. 

 The new samples should not duplicate any of the elements selected for 

 the original sample set. Experience has shown that this second itera- 

 tion of sampling has always been sufficient to meet the sample size 

 requirements; however, it is recommended that after data are acquired 

 from any sample set a new sample size calculation should be made using 

 all the data collected. 



Once the confidence and accuracy requirements for calculation of 

 the average facility condition (mean and standard deviation) have been 

 met, the expected maintenance and repair requirements should be pro- 

 jected by calculating the percentage of piles falling within each main- 

 tenance category using the probability distribution function developed 

 from the sample data. The expected percentage for each of these cate- 

 gories is an attribute of the population; therefore, the required sample 

 size must be calculated using Equation 9 or 10, even though the data 

 were acquired from a measurement of a variable. 



If the original sample size was selected to determine an attribute 

 for which measurement data were not appropriate (i.e., proportion of 

 piles with marine borer damage), then a statistical analysis will pro- 

 vide an estimate of the mean proportion value, the standard error of 

 proportion, and the confidence interval. There should be no reason to 

 require additional samples if the initial assumption of proportion was 

 the worst case of 50 percent. 



SUMMARY 



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. 



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