A Method for Comparing the Precision of a Set of Age Determinations

1981 ◽  
Vol 38 (8) ◽  
pp. 982-983 ◽  
Author(s):  
R. J. Beamish ◽  
D. A. Fournier
Keyword(s):  
Age Determination ◽  
Percent Error ◽  
Percent Agreement ◽  
Age Determinations

An index of average percent error is a better estimate of the precision of age determinations than the conventional percent agreement method because it is not independent of the age of a species.Key words: age determination, aging errors

A Statistical Method for Evaluating the Reproducibility of Age Determination

1982 ◽  
Vol 39 (8) ◽  
pp. 1208-1210 ◽  
Author(s):  
William Y. B. Chang
Keyword(s):  
Statistical Method ◽  
Fish Species ◽  
Coefficient Of Variation ◽  
Age Determination ◽  
Statistical Test ◽  
Absolute Difference ◽  
Percent Error ◽  
Percent Agreement ◽  
Coefficients Of Variation ◽  
Variation Index

The coefficients of variation and the index of precision provide a statistical test of reproducibility of aging between readers. Because the coefficients of variation and the index of precision incorporate the averaged year-class of a fish species, they are free from the shortcoming of the percent agreement method. Because variance is a better estimator than absolute difference, the coefficient of variation is a stronger estimator than the index of average percent error in providing a test statistic.Key words: age determination, coefficients of variation, index of precision, average percent error, percent agreement

Analysis of Bone Age Data From National Cooperative Growth Study Substudy VII

PEDIATRICS ◽  
1999 ◽  
Vol 104 (Supplement_5) ◽  
pp. 1031-1036
Author(s):  
Stephen F. Kemp ◽  
Judy P. Sy
Keyword(s):  
Age Determination ◽  
Bone Age ◽  
Strongly Correlated ◽  
Growth Study ◽  
Gh Therapy ◽  
Pubertal Stage ◽  
Significant Difference ◽  
Clinically Significant ◽  
National Cooperative ◽  
Age Determinations

National Cooperative Growth Study substudy VII was conducted 1) to compare standardized hand–wrist and knee bone age determinations in pubertal children treated with growth hormone (GH); 2) to compare local determinations of bone ages with centrally determined bone ages; 3) to relate the response to GH therapy to the bone age determinations; and 4) to ascertain the predictive value of each type of bone age determination. Eligible subjects were those in the National Cooperative Growth Study who were at Tanner pubertal stage 2 or greater for breasts (girls) or genitals (boys). Radiographs of the hand–wrist were taken annually, and radiographs of the knee were taken at the beginning and the end of the study. Separate bone age determinations were made from these radiographs. A combined hand–wrist and knee bone age determination also was derived. There were 990 patients in the study; in 925 (677 boys), there were both hand–wrist and knee bone age determinations from the baseline pubertal radiographs. There was only one radiographic assessment in 496 patients, two in 205 patients, and three to eight in the remaining patients. The strongest correlation was between the hand–wrist bone age and the hand–wrist plus knee bone age (r = .995). Also strongly correlated were knee with hand–wrist (r = .872) and knee with hand–wrist plus knee (r = .914). For none of these bone age methods was any statistically significant difference found between the methods. The locally determined bone ages correlated strongly with the centrally determined bone ages for knee (r = .850), hand–wrist (r = .928), and hand–wrist plus knee (r = .930); however, the locally determined knee and hand–wrist values were less (by ∼0.3 year) than the centrally determined values. These differences, however, do not appear to be clinically significant.

Rubidium and Strontium age determination of some Pre-Cambrian granitic rocks, S.E. Uganda

1971 ◽  
Vol 108 (5) ◽  
pp. 353-360 ◽  
Author(s):  
R. A. Old ◽  
D. C. Rex
Keyword(s):  
Age Groups ◽  
Age Determination ◽  
Granitic Rocks ◽  
Age Limit ◽  
Age Determinations

SummaryWhole rock rubidium-strontium age determinations on granitic bodies in S.E. Uganda give ages of 2930 m.y. for the Masaba Granite and 2430 m.y. for the Buteba Granite and granitic gneisses. The former age is considered to represent the upper age limit of the post-Nyanzian orogeny, and 2430 m.y. the upper age limit of the post-Kavirondian orogeny. A second isochron age of 2100 m.y. for the Masaba Granite may reflect a second intrusion, or remobilization of part of the original granite associated with the Buganda–Toro orogeny. Tentative correlations are suggested between these age groups and others within the Tanzanian Shield and beyond.

scholarly journals Routine K/Ar age determinations on rocks from Greenland carried out for GGU in 1970

1971 ◽  
Vol 35 ◽  
pp. 52-60
Author(s):  
D Bridgwater
Keyword(s):  
Analytical Data ◽  
Age Determination ◽  
Geological Significance ◽  
Reconnaissance Survey ◽  
Geological Work ◽  
The University ◽  
Age Determinations

The programme of commercial age determinations started in 1969 (Bridgwater, 1970) was continued to supplement the work carried out by the University of Copenhagen (Larsen, this report). The material dated represents a rather heterogeneous collection of rocks from many parts of Greenland about which information was required for current geological work but which were not included in existing age determination projects. All the results obtained are listed whether or not the "ages", have a clear geological significance, since a major reason for carrying out this form of reconnaissance survey is to test the suitability of K/Ar methods for making more detailed studies. Full analytical data is available on request from GGU. Unless otherwise stated the results given are means of three determinations.

scholarly journals Bomb dating, age validation and quality control of age determinations of monodontids and other marine mammals

2014 ◽  
Vol 8 ◽  
Author(s):  
Steven E Campana ◽  
Robert EA Stewart
Keyword(s):  
Quality Control ◽  
Marine Mammals ◽  
Age Determination ◽  
Age Validation ◽  
Age Bias ◽  
Bomb Radiocarbon ◽  
Control Protocols ◽  
The 1960S ◽  
Age Determinations

Methods for confirming the accuracy of age determination methods are reasonably well established in fishes, but the millions of routine age determinations which take place every year require their own quality control protocols. In contrast, methods for ensuring accuracy in age determination of monodontids and other marine mammals are still being developed. Here we review the basis and application of bomb radiocarbon to marine mammal age validation, highlighting its value for providing unambiguous estimates of age for belugas and other long-lived animals which form growth bands. Bomb radiocarbon is particularly useful for marine mammals, given that the age of an individual animal can be determined to within ±1-3 years, as long as it was alive during the 1960s. However, ongoing age determinations require careful monitoring to ensure that age interpretations remain consistent across ages and through time. Quality control protocols using reference collections of ageing material, in conjunction with age bias plots and measures of precision, are capable of detecting virtually all of the systematic ageing errors that often occur once age determinations of an animal become routine.

scholarly journals The geochronology of the Scoresby Sund area Progress report I: Rb/Sr mineral ages

1971 ◽  
Vol 37 ◽  
pp. 55-57
Author(s):  
B.T Hansen ◽  
R.H Steiger
Keyword(s):  
Age Determination ◽  
Crystalline Rocks ◽  
Progress Report ◽  
Rock Types ◽  
Age Determinations

A general age determination programme has been proposed for the crystalline rocks of the Scoresby Sund region. The various field geologists are contributing to this by delivering material of significant rock types from their individual areas, and subsequently the actual age-determinations are carried out at the "Institut für Kristallographie und Petrographie" of the "Eidg. Technische Hochschule" in Zürich.

How Old are Tropical Trees? the Persistence of a Myth

IAWA Journal ◽  
1999 ◽  
Vol 20 (3) ◽  
pp. 255-260 ◽  
Author(s):  
Martin Worbes ◽  
Wolfgang Johannes Junk
Keyword(s):  
South America ◽  
Growth Rates ◽  
Age Determination ◽  
Tropical Trees ◽  
Pioneer Species ◽  
Annual Rings ◽  
Hollow Trees ◽  
Cariniana Legalis ◽  
Direct Counting ◽  
Age Determinations

The recent report of ancient trees in the Amazon region (Chambers et al. 1998) with a maximum radiocarbon dated age of about 1400 years for the long-living pioneer species Cariniana micrantha is discussed in the light of dendrochronological age determinations from Africa and South America together with the results of indirect age estimations from other sources. There is a tendency in the literature to considerably overestimate the maximum ages of tropical trees. Age determination by the direct counting of annual rings and making estimations for hollow trees by measuring growth rates and diameters result in ages between 400 and 500 years for the largest trunk dimensions, e.g. in Cariniana legalis.

scholarly journals Models for Pop I stars: implications for age determinations

2008 ◽  
Vol 4 (S258) ◽  
pp. 177-188 ◽  
Author(s):  
Georges Meynet ◽  
Patrick Eggenberger ◽  
Nami Mowlavi ◽  
André Maeder
Keyword(s):  
Age Determination ◽  
Stellar Models ◽  
Age Determinations

AbstractStarting from a few topical astrophysical questions which require the knowledge of the age of Pop I stars, we discuss the needed precision on the age in order to make progresses in these areas of research. Then we review the effects of various inputs of the stellar models on the age determination and try to identify those affecting the most the lifetimes of stars.

The geochronological significance of argon-40/argon-39 age determinations on White Whin from the northern Pennine orefield

1968 ◽  
Vol 307 (1490) ◽  
pp. 251-266 ◽  
Keyword(s):  
Clay Minerals ◽  
Clay Mineral ◽  
Hydrothermal Alteration ◽  
Age Determination ◽  
Hydrothermal Activity ◽  
Work Support ◽  
Natural Isotope ◽  
Minimum Age ◽  
Widespread Phenomenon ◽  
Age Determinations

Controversy regarding the age and character of mineralization in the northern Pennine orefield is reviewed in the context of recent geological and geochronological research in the region, and a number of the unresolved problems are tabulated. A new method of potassium-argon radioisotopic age determination which utilizes the conversion of the natural isotope 39 K in a rock or mineral to the isotope 39 Ar by neutron irradi­ation is described in outline. This method avoids some of the limitations of conventional potassium-argon age determination, and, among other advantages, makes the measurement of the radioages of clay minerals possible. A geochronological and petrological investigation of White Whin samples from the northern Pennine orefield is reported in full, and eighteen new age determinations, mostly upon clay mineral concentrates are presented. The conclusions that can be drawn from this work support a hypothesis of repeated hydrothermal mineralizations within the area of the northern Pennine orefield: the first within the period 284 ± 40 My with subsequent maxima of hydrothermal activity occurring at intervals. At least two of these subsequent episodes have been identified: one around a minimum age of 230 My and another, very important episode occurring around 170 My. Comparison of these results with histograms of (1) all radio­ages of British rocks and (2) radioages from British dolerites and basalts only, suggests that episodic hydrothermal alteration of pre-existing rocks may be a widespread phenomenon in Britain.

ABSOLUTE AGE OF THE FISSET BROOK FORMATION AND THE DEVONIAN-MISSISSIPPIAN BOUNDARY, CAPE BRETON ISLAND, NOVA SCOTIA

1964 ◽  
Vol 1 (3) ◽  
pp. 159-166 ◽  
Author(s):  
R. F. Cormier ◽  
A. M. Kelly
Keyword(s):  
Nova Scotia ◽  
Volcanic Rocks ◽  
Age Determination ◽  
Cape Breton Island ◽  
Rock Samples ◽  
Cape Breton ◽  
Absolute Age ◽  
Age Determinations ◽  
Good Agreement

The Fisset Brook formation of sedimentary and volcanic rocks crops out in the Cheticamp area of Cape Breton Island, Nova Scotia. Its stratigraphic age has been determined as earliest Mississippian using spores contained in the sedimentary members. A rubidium–strontium age determination using whole-rock samples of the volcanic members has yielded an age of 349 ± 15 million years. This is in good agreement with age determinations elsewhere for the Devonian–Mississippian boundary. Similar rocks exposed to the east of Lake Ainslie, some thirty miles to the southwest, give an identical age, 348 ± 20 million years. These rocks are clearly correlative with the Fisset Brook formation. Mixed sedimentary and volcanic rocks in the Cape St. Lawrence area, some thirty miles to the northeast of Fisset Brook, appear to be significantly older, 462 ± 25 million years, and should be considered tentatively as Ordovician in age.

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