CHAPTER4 RESULTS AND ANALYSIS OF DATA The reliability of the results of certain average values used in this report to express the - radioactivity of a group of organisms is subject to the following considerations: , 1. Nonrandom selection of specimens: In the field, collection of specimens was directed toward obtaining certain species at all stations, if possible, and supplementingthis collection with whatever other species were available. When a large numberof a single group of organisms was available, only a small percentage of the specimens was collected, whereas all the specimens may have been collected for another group of organisms which were less abundant. Hence the specimens are represented qualitatively rather than quantitatively in the field col- - lection and also in the samples used for courting. 2. Random selection of tissues: In some instancesthe activity of preshot invertebrates for a collecting station was estimated by averaging aJl the samples counted, irrespective of tissue or species. Such an estimate is an average of plate counts and not an average of the preshot invertebrates. For someof the fish the total activity of individuals was determined, not by randomly selecting by tissues but by using weighted samples of all tissues. The activity - of the group (fish) was then determined by averaging the values for the individuals. Although the two methods for determining the group average differ in the degree of refinement of the data, one viewpoint is that the method used for the preshot invertebrates adequately describes the trends and that, for these organisms, further refinement is not warranted because of the nature of the errorsin the data. 3. Variance of sample counts: Variance both within groups and between groups was often great. The greatest variance and also the highest specific activity were found in those tissues with radioactivity from surface contamination, e.g., algae in the digestive tract of fish, sand in the gut content of the sea cucumber, algae growing on the carapace of the crab, or fall-out particles on the surface of iand plants. On the other hand, the radioactivity of tissues with absorbed isotopes only, such as muacle, bone, and liver, was less variable and was usually lower. Consequently it is believed that the greatest cause of variance in the sample counts was due to the amount and type of food in the digestive tract and/or the materials on external surfaces. 4. Number of items in a sample; Small samples resulted from breaking down thecoilection into small groups, such as species. The combination of a few samples and a large value for tre variance considerably impairs the reliability of results. In view of these considcrations the best estimate of the absolute value of the radioactivity of a group of organisms at a collecting station is an average of the valuzs for the individual organisms. However, for comparison of activities by collecting stations, the best estimate is made by comparing similar species and tissues. Because the variance both between and within species was often great and the number of samples was limited, the most that can be obtained from these data are trends and certain relative values. 26 NCLASSIFIED -