46 second degree in age was used when there was a significant departure from linearity. The criteria vibratory sense, hand grip, light extinction time, hand-tally count, and body potassium showed significant sex differences, and were therefore scaled for each sex (0 to 100%). An attempt to correlate a combined “‘physio- logic” age score with chronological age was done by obtaining a weighted average score for combined criteria for each age group (see Table 22). The absolute valuesof the correlation coefficients were used as the weighting factor. This has intuitive appeal, since the influence on the final combined score of any particular aging criterion is proportional to the absolute value ofits correlation with age. Results of Aging Studies The results of these tests are presented graphically in Figures 34 to 48 and in Table 22. The mean values for each decade starting at age 20 are plotted at the midpoint of that decadefor exposed and unexposed groups separately and combined, along with the standarderrors of the means. The numberbeside each point is the number of people tested. The curve orstraight line (whichever best represents the particular data) is drawn and its equation presented. The coefficient of correlation with age andsignificanceis also presented. Mostof the criteria show good correlation with aging. It is apparent that mostofthe criteria show the least change with age in the younger age groups, from 20 to 40 years of age, particularly systolic blood pressure, hearing, visual acuity, neuromuscular function, and skin retraction. Above about40 years of age the criteria show the greatest change. With a few criteria, changes in the older age grouptend to leveloff or be less steep (accommodation, visual acuity, skin looseness, and cholesterol). In Table 22 age and radiation dependenceof these criteria are presented. Thecriteria are arranged in descending orderof correlation with aging as shown bythe correlation coefficients. For those criteria in which sex differences were apparent, the 7 values for the two sexes were averagedto determinethe over-all correlation with aging. Though there wereisolated significant differences between the exposed and unexposed age groups for some criteria, no meaningful pattern emerged. The table showsthat the correlation with radiation ef- fects, in comparing exposed and unexposed groups, is not significant at the 5% level for any of the criteria. The over-all 7% increase in agingeffects in the exposed group is not significant ( p =0.27). In Figure 48 the composite weighted biological or physiologic age scores are plotted against chronological age (means per decade). Combined mean values for exposed and unexposed groupsarealso presented with standarderrors of the means. The over-all correlation of the biological age scores with chronological age is very good. The biological “age curve” (Figure 48) showsthat thereis less change in the younger age groups than thereis after about age 40. Mean values for exposed and ‘unexposed are notsignificantly different. Discussion of Aging Studies Though the criteria presented in this report show changeswhicharedefinitely correlated with chronological age on a group basis, such correlation is much less accurate on anindividual basis. These tests of aging are least useful in the younger age groups (20 to +0 years of age), since most of the criteria either are not present until later or if present showslight increase during this age period. Therefore, moresensitive tests are needed to show aging in these groups. Effects of radiation on aging as measured by these parameters were not detected in this population. Perhapsthe tests were not sensitive enough to detect such effects at the level of radiation ex- posure sustained. It is not known if any of the “aging parameters” ordinarily associated with senescenceare necessarily associated with irradiation aging, since the latter is very poorly defined or understood. Even if they were, this would not necessarily meanthat they are related to mortality, which is a more pertinent correlation. Such criteria as hair graying, arcus senilis, neuromuscular function, etc., would not seem to have any obvious relation to mortality. On the other hand, loss of vigor and organ disfunction could well predispose to the developmentofold age diseases which would enhance mortality. Increase in mortality andlife shortening in the exposed Marshalleseis difficult to assay in view of the small numbersof people involved andtheslightly greater proportionofolder people originally in the exposed group compared with the unexposed group. Oneradiation effect which might beclassified underagingis the inducementof malignant disease