Age-predictive Equations Research Articles

Estimation of Dental Age by Mandibular Third Molar Through Digital Orthopantomogram Using Modified Demirjian Method In South Indian Population Visiting A Dental College- A Retrospective Study

Aim: The aim of this study was to evaluate the applicability of Demirjian’s method for dental age assessment in a group of South Indian population and to develop an age-predictive equation suitable for the studied group. Subjects and methods: In this retrospective, blind, cross-sectional study, 120 Digital Orthopantomograms were selected from the archived medical files of patients attending Dental College and evaluated to estimate dental age. Results: Age was over estimated for almost all of the studied subjects with an accuracy range from 0.18 to 1.19 years for males and from 0.08 to 0.87 years for females, with the exception of two age subgroups Conclusion: Demirjian’s method is very useful and suitable for the South Indian population. The development of a prediction equation and the introduction of adaptable conversion tables to transform the maturity score into a dental age for the South Indian population with population-specific samples may be suitable alternatives.

Are age-predicted equations valid in predicting maximum heart rate in individuals after stroke?

Purpose To investigate the validity of six age-predicted maximum heart rate (HRmax) equations after stroke. Material and methods Sixty individuals (54 (12) years; 64 (69) months after stroke) were included. A Cardiopulmonary Exercise Test (CPET) performed on a treadmill obtained the HRmax. The most used age-predicted equations were investigated: (1) 220-age, proposed by Fox; (2) 206.9– (0.67 × age), proposed by Gellish; (3) 208– (0.7 × age), proposed by Tanaka; (4) 216.6– (0.84 × age), proposed by Astrand; (5) 164– (0.72 × age) and (6) 200– (0.92 × age) proposed by Brawner. Results No statistically significant agreement was found between the HRmax obtained by the CPET and the one predicted by the equations 1–5 (–0.18 ≤ 95% confidence interval ≤0.79). A significant and moderate agreement was found between the HRmax obtained by the CPET and the one predicted by equation (6) (95% CI= 0.05–0.75; Intraclass Correlation Coefficient= 0.51). Bland-Altman plots showed that equations (1–4) and (6) overestimated the HRmax. Equation (6) presented the lower mean difference. Conclusions The equations developed for non-disabled individuals (1–4) are not adequate to be used in individuals after a stroke. Equation (6) (Brawner) showed the best results to be used in individuals after stroke; however, it should be used cautiously.

Magnetic Resonance Imaging Of Calvarial Diploe Thickness for Sex And Age Estimation of A Sample Of Egyptian Population

Background: Magnetic resonance imaging (MRI) is a mainstay radiological technique that is becoming more desirable in forensic identification for its non-invasive, non-ionizing and highly precise nature. Objectives: This study aimed to investigate whether sex and age could be estimated based on Calvarial Diploe Thickness (CDT) using MRI in a sample of the Egyptian population. Methods: The study was conducted on cranial MRI images of 306 adult Egyptians. For sex and age estimation, seven CDT measurements were assessed on 256 cranial MRI images of known sex and age. A binary logistic regression equation was developed for sex prediction. Multivariate linear regression analyses were performed to generate age prediction equations; equation (1), gender was included, while equation (2) was irrespective of gender. All regression equations were tested on 50 cranial MRI images. Results: The results revealed a significant binary logistical regression model for sex prediction of r2 0.442 and classification accuracy 71.6%. The Receiver Operating Characteristic (ROC) curve showed an area under the curve (AUC) 0.816, sensitivity 76.6 %, and specificity of 70.5%. Testing the equation showed accuracy for identifying males (78.2 %), accuracy for identifying females (70.4 %), and overall accuracy (74 %). Regarding age estimation, Pearson correlation showed no statistically significant correlation between age and all CDT measurements. Age prediction multivariate linear regression models (sex-stratified/sex-pooled) were statistically insignificant, with very low adjusted r2 and high standard error of estimate. Testing the multivariate linear regression equations showed Mean Absolute deviation (MAD) between the chronological age and predicted age of 9.09254 years and Mean Absolute Percentage Error (MAPE) of 28.458% for the multivariate linear regression equation (1) and MAD of 8.94469 years; and MAPE of 27.9829% for the multivariate linear regression equation (2). Conclusion: We concluded that the studied CDT measurements could be included as a new candidate in MRI-based sex estimation for Egyptians while are unfavorable for estimating age. Our results provide preliminary results for assessing a new approach for estimating sex and age for Egyptians. Applying such parameters on a greater sector of Egyptians for both sex and age estimation is highly recommended.

Skeletal age and explosive strength in young volleyball players

Identifying diferent anthropometric, physiological and motor aspects is essential to obtain success in sports practice. However, these components may be developed in same age subjects diferently, in part due biological development. he aim of the study was compare and correlate the explosive strength to biological maturation by sex, obtained by estimation of skeletal age based on anthropometric variables. he sample consisted of 239 subjects of both sexes, aged 10 to 13 years. Maturation was assessed by skeletal age predictive equation and upper and lower limbs explosive strength using medicine ball throw test and vertical jump, respectively. Skeletal age was assessed by skeletal age using a predictive anthropometrical based equation. Upper and lower limbs explosive strength were evaluated by medicine ball throwing test and vertical jump test, respectively. Post hoc analysis showed delayed biological development subjects had worst medicine ball throwing test performance than accelerated boys (p=0.001; d=0.96) and girls (p< 0.01; d= 2.01); regarding to vertical jump test, worst performance was also detected to maturational delayed boys when compared to accelerated ones (p=0.24; d=1.1) and girls (p=0.007; d=0.75). Regression analysis showed skeletal age explained variance of 36% and 19.2% for boys and 45.2% and 16.1% for girls upper and lower limbs explosive strength. Skeletal age is positively related to upper and lower limbs explosive strength and show higher performance for accelerated biological development young players when compared to delayed ones, independently from sex.

A radiographic study of permanent molar development in wild Virunga mountain gorillas of known chronological age from Rwanda.

While dental development is important to life history investigations, data from wild known-aged great apes are scarce. We report on the first radiographic examination of dental development in wild Virunga mountain gorillas, using known-age skeletal samples recovered in Rwanda. In 43 individuals (0.0-14.94 years), we collected radiographs of mandibular molars, and where possible, cone beam CT scans. Molar crown and root calcification status was assessed using two established staging systems, and age prediction equations generated using polynomial regression. Results were compared to available data from known-age captive and wild chimpanzees. Mountain gorillas generally fell within reported captive chimpanzee distributions or exceeded them, exhibiting older ages at equivalent radiographic stages of development. Differences reflect delayed initiation and/or an extended duration of second molar crown development, and extended first and second molar root development, in mountain gorillas compared to captive chimpanzees. However, differences in the duration of molar root development were less evident compared to wild chimpanzees. Despite sample limitations, our findings extend the known range of variation in radiographic estimates of molar formation timing in great apes, and provide a new age prediction technique based on wild specimens. However, mountain gorillas do not appear accelerated in radiographic assessment of molar formation compared to chimpanzees, as they are for other life history traits. Future studies should aim to resolve the influence of species differences, wild versus captive environments, and/or sampling phenomena on patterns observed here, and more generally, how they relate to variation in tooth size, eruption timing, and developmental life history.

Postnatal growth and age estimation in Scotophilus kuhlii.

Adequate postnatal growth is important for young bats to develop skilled sensory and locomotor abilities, which are highly associated with their survival once independent. This study investigated the postnatal growth and development of Scotophilus kuhlii in captivity. An empirical growth curve was established, and the postnatal growth rate was quantified to derive an age-predictive equation. By further controlling the fostering conditions of twins, the differences in the development patterns between pups that received maternal care or were hand-reared were analyzed to determine whether the latter developed in the same manner as their maternally reared counterparts. Our results indicate that both forearm length and body mass increased rapidly and linearly during the first 4 weeks, after which the growth rate gradually decreased to reach a stable level. The first flight occurred at an average age of 39 days with a mean forearm length and body mass of 92.07% and 70.52% of maternal size, respectively. The developmental pattern of hand-reared pups, although similar to that of their maternally reared twin siblings, displayed a slightly faster growth rate in the 4th and 5th weeks. The heavier body mass of hand-reared pups during the pre-fledging period may cause higher wing loading, potentially influencing the flight performance and survival of the bats once independent.

Biometric Method for the Ossification Evaluation of Children from Birth Up to the Ages of Two and Four – Applied to the Metacarpal and Phalanxes in Spanish Longitudinal Series

Aim: This work, based on the Spanish longitudinal growth and development series done at the Andrea Prader Center, Zaragoza, Spain, studied children up to the age of twenty years. It aims to contribute to a practical and accurate numerical method to calculate the bone age of the studied children, from birth to two and four years. Methods: The total sample of the study was 160 healthy children (73 males and 87 females). Every child underwent annual radiography on his/her left hand at the Miguel Servet Hospital in Zaragoza, Spain. Using measurements of the Tanner II-Rus method, the maximum epiphyseal distances of the subjects were studied. Results: As a result, we have developed an index called the Metacarpal-Phalanx Index, closely correlated with the chronological age of the child, which creates bone age prediction equations. Another index called Index Valuation Ossification of the Metacarpal-Phalangeal, obtained through the above, allowed us to compare the results to Gaussian shape equivalences, thus revealing the ossifying status of the child, and whether it is late, early or insignificant.

Comparisons of Age-Predicted Maximum Heart Rate Equations in College-Aged Subjects

This study investigated the accuracy of age-predicted equations to predict heart rate maximum (HRmax) in a college-age sample and establish efficacy of short-duration anaerobic capacity tests to determine the actual HRmax. A criterion HRmax (CHRmax) was obtained from 96 (52 men and 44 women, age = 22.0 ± 2.8 years, height = 163.9 ± 9.5 cm, 70.6 ± 14.7 kg, resting HR = 68.9 ± 11.2 b·min) healthy volunteers during 2 200-m sprint trials on a standard track. Maximal effort was confirmed via plasma lactate ≥7 mmol·L(-1) and rating of perceived exertion ≥17 points. The CHRmax was compared to 7 age-predicted HRmax equations: Fox et al., 3 equations from Gellish et al., Tanaka et al., and gender-specific equations from Fairbarn et al., and Hossack et al. Descriptive statistics and standard errors of estimate (SEEs) were calculated. One-way analysis of variance was used to assess differences between the criterion HRmax and the age-predicted HRmax from the 7 equations. The predicted HRmax from the Fox equation and those of Gellish(3), Tanaka, and Hossack were all significantly higher (p ≤ 0.05) than the CHRmax. The Fox equation resulted in overpredicting HRmax in 88.5% of the cases compared to the CHRmax. Compared to the CHRmax, the age-predicted HRmax equations resulted in the following percentages of the CHRmax: Fox = 104.8%, SEE = 12.7; Gellish(1) = 95.2%, SEE = 12.2; Gellish(2) = 99.6%, SEE = 8.3; Gellish(3) = 101.8%, SEE = 9.1; Tanaka = 102.0%, SEE = 9.3; Fairbarn = 100.1%, SEE = 8.5; and Hossack = 105.2%, SEE = 13.9 of CHRmax. It was concluded that the Gellish(2) and Fairbarn equations were the most accurate of the age-predicted HRmax equations in a college-age population. In practical application, 2 200-m sprint trials provide a reasonable estimate of HRmax compared to a graded exercise test.

혈액세포의 텔로미어 함량을 이용한 소의 연령예측

텔로미어란 진핵세포의 염색체 양 말단에 있는 DNA-단백질 복합체로서, 특정단백질과 TTAGGG의 반복염기서열로 구성되어있다. 이들의 기능은 핵 내 염색체의 안정성에 본질적으로 작용함으로 세포의 노화와 직접적 관련이 있다고 알려져 있다. 본 연구에서는 소의 간기상태의 백혈구 세포를 대상으로 연령별, 품종별, 성별간 telomeric DNA 함량을 분석하여 이러한 요인들이 텔로미어 함량에 미치는 영향을 살펴보고 또한, 텔로미어 함량을 이용한 개체의 연령예측 가능성을 제시하고자 하였다. 소의 텔로미어의 함량 분석은 1개월령에서 166개월령의 한우 및 홀스타인종 460두를 대상으로 telomeric DNA probe를 이용한 Q-FISH 방법으로 분석하였다. 분석 결과 소에 있어서 연령이 증가함에 따라 telomeric DNA 함유율이 일관되게 점진적으로 감소되는 양상을 보였다. 소의 품종간 telomeric DNA 함유율을 비교한 결과 한우의 telomeric DNA 함량이 홀스타인종에 비해 유의적으로 높게 나타났으며, 성별 간에도 수컷이 암컷에 비해 유의적으로 높은 telomeric DNA 함유율을 나타내어 품종별, 성별 모두 텔로미어 함유율의 유의적인 차이가 있음 확인 할 수 있었다(P<0.01). 따라서 요인별 유의적 차이가 있음으로 한우 암컷 및 홀스타인 암컷에 대한 각기 연령예측 회귀함수를 추정하였다. Telomeric DNA 함량을 독립변수(X)로 하고, 연(월)령을 종속변수(Y)로 설정하여 2차회귀식을 도출한 바 한우 암컷의 경우 <TEX>$\hat{Y}$</TEX>=<TEX>$38.102X^2$</TEX>-220.103X+318.309(P<0.0001, <TEX>$R^2$</TEX>=0.8019)이고, 홀스타인 암컷은 <TEX>$\hat{Y}$</TEX>=<TEX>$42.799X^2$</TEX>-199.682X+242.106(P<0.0001, <TEX>$R^2$</TEX>=0.8379)으로 분석되었다. 이상의 두 회귀식 모두 유의한 함수로 결정계수(<TEX>$R^2$</TEX>) 또한 0.8 이상의 높은 상관 값을 보임에 따라 본 회귀식으로 소의 연령 예측이 가능함을 제시하고자 한다. Telomeres at the end of chromosomes consist of tandem repeats of (TTAGGG)n DNA sequence and associated proteins. Telomeres have the essential functions in chromosome stability and genome integrity and are hence related to cell senescence and cancer. This study was carried out to quantify the amount of telomeric DNA and establish age prediction equations by using the quantity of telomeric DNA for cattle. Analysis of the telomere quantity of the lymphocytes was performed at different age, across breeds and between different sexes of cattle. We quantified the amount of telomeric DNA by the Q-FISH technique using the telomeric DNA probe in 460 cattle at age of 1~166 months in Korean Cattle and Holstein breeds. In results, we found that the amount of telomeric DNA decreased gradually with age. The amount of telomeric DNA of Korean Cattle was significantly higher than that of Holstein breed (P<0.01). In addition, the amount of telomeric DNA in male was significantly higher than that in female (P<0.01). Using the relationship between age and the amount of telomeric DNA in cattle, age predicting equations were established as a result of regression analysis. Because sex and breeds influenced telomeric DNA quantity, the age prediction equations were estimated separately in Korean Cattle females and Holstein females. The regression equations were <TEX>$\hat{Y}$</TEX>=<TEX>$38.102X^2$</TEX>-220.103X + 318.309 (P<0.0001, <TEX>$R^2$</TEX>=0.8019) in Korean Cattle females and <TEX>$\hat{Y}$</TEX> = <TEX>$42.799X^2$</TEX> - 199.682X + 242.106 (P<0.0001, <TEX>$R^2$</TEX> = 0.8379) in Holstein females, where the X was quantity of telomeric DNA and Y was predicted age in months. These equations predicted the age of cattle with high significance and accuracy and have high R square values. Thus, it could be possible to scientifically predict the age using the above equations for Korean Cattle and Holstein females.

Postnatal Growth and Age Estimation in the Ashy Leaf-Nosed Bat,Hipposideros cineraceus

We quantified changes in body mass, forearm length, and the total length of the epiphyseal gap of the fourth metacarpal-phalangeal joint of the ashy leaf-nosed bat (Hipposideros cineraceus) based on mark-recapture data obtained in Fangkong Cave in Hekou, Yunnan Province, China. We used these data to develop empirical growth curves, to derive growth rates, to establish age-predictive equations, and to compare growth parameters based on three nonlinear growth models. Forearm length and body mass of pups followed a linear pattern of growth until day 17, with mean growth rates of 0.81 mm/day and 0.09 g/day, respectively and thereafter their growth rates increased more slowly. The length of the epiphyseal gap initially increased linearly up to day 13 and then decreased linearly at a mean rate of 0.07 mm/day until day 37. An equation for estimating age based on forearm length was valid when this dimension was ≤ 27.6 mm, whereas the equation based on the length of the epiphyseal gap was valid for forearm lengths...

Regression Analysis of Walking Parameters for the Age-Predictive Equation

We tried to establish an age-predictive equation from kinematic and kinetic parameters during walking using the 2007 Okada database of Japanese elderly. Some predictive equations were established for each gender (109 males and 139 females)--once for all variables, second for the stepwise variable selection method. The range of motion (ROM) of knee and hip and step length are the stable parameters in age-predictive models for both genders. Although the model achieved the Minimum Akaike's Information Criterion Estimate (MAICE), it did not reflect sufficiently the regimes of variable selection.

Postnatal Growth and Age Estimation in Big-Footed Myotis,Myotis macrodactylus

We quantified the length of the forearm, the body mass and the length of the total gap of the fourth metacarpal-phalangeal joint of marked individuals of big-footed myotis bats (Myotis macrodactylus) from birth to flight in Dalazi Cave in Ji'an, Jilin Province, China. By using these data, we develop empirical growth curves, derive growth rates, establish age-predictive equations, and compare growth parameters based on three nonlinear growth models. Neonates of M. macrodactylus were born within a half-month period, with length of forearm averaging ca. 38.4% of the size of adult females and body mass averaging ca. 39.6% of their mother's body mass. Length of forearm increased linearly until 14 days after birth (growth rate = 1.20 mm/day), as did body mass until 11 days after birth (growth rate = 0.32 g/day). The length of the total gap of the fourth metacarpal-phalangeal joint decreased linearly from 13 days to 45 days of birth. Two most appropriate linear regression equations predicting the age of young bats were derived from forearm length ( ± SE) from 15.35 ± 0.96 mm to 33.24 ± 1.87 mm and the length of the epiphyseal gap from 13 to 45 days. These two equations make it possible to estimate the age of pups from 1 to 45 days of age in M. macrodactylus. Of the three nonlinear growth models (logistic, Gompertz, and von Bertalanffy), the logistic equation provides the best fit to the empirical curves for length of forearm and body mass.

Statistical Issues of Regression Analysis on Development of an Age-Predictive Equation

Several statistical information criteria and other statistical issues such as residual examinations and multi-collinearity in regression analysis were argued to establish the predictive equation of age from physical fitness measurements. These independent variables of physical fitness, body composition, two blood pressures, and bone strength were taken from 31 Japanese males (48 +/- 11.9 years old) living in rural areas. The following equation was selected as the optimal one according to Akaike's information criterion: ŷ = 90.0 -1.294 * SITUP - 0.467 * MAP - 0.094 * BALANCE (R = 0.837). When all ten variables were included in the initial equation, R was 0.864, and the highest R* (R adjusted for d.f.) was observed at the fifth step.

Establishment of Age-predictive Equation for Japanese Women Based on Simple Physical Fitness Measurements and Blood Pressure

The purpose of this study was to discuss the procedures for establishing indices for physical senility from simple physical fitness tests through linear regression analysis. The fluctuation of residuals obtained from the various regression analyses and the statistical procedures for dealing with the variables when the assumptions concerning the residuals were contradicted, were discussed. In this study, 168 females (mean age 37.7, SD 11.3, range 20 to 65years) who were registered with one occupational insurance organization were examined. They each underwent tests to establish readings for seven variables, including five physical fitness tests: standing trunk flexion (FLEX), sit-ups in 30seconds (SIT-UP), vertical jump (VERT), repetitious side step in 20seconds (SIDE), and step test (STEP-ME). Two blood pressure readings while at rest were also taken (SBP, DBP). The results can be summarized as follows. In the forward stepwise regression analysis, the order of entered variables was VERT (R=0.637), SIT-UP (R=0.673), DBP (R=0.696), FLEX (R=0.704), and SIDE (R=0.717). The equation is y=61.38-0.569×(VERT)-0.513×(SITUP)+0.183×(DBP)+0.283×(FLEX)-0.328×(SIDE). Minimum AIC estimates (MAICE) were achieved for this equation. The correlation coefficient between residuals and predicted value was 0.345 (p<0.05). To satisfy the assumptions of the standard regression model, the researchers worked with transformed variables instead of working with original variables. The transformations of the raw data into logarithms and into reciprocals is described. According to the rules of variable elimination using ridge regression analysis, SBP and STEP-ME were eliminated from the set of seven variables. However, an examination of the residuals indicated that there were no advantages with using these transformations compared to the general linear model using raw data. The ratio of the predicted age for each client obtained from the predictive equation and chronological age is regarded as a marker of aging. Therefore, it is necessary for researchers to examine what kind of life styles result in such individual differences.

Intrinsic and extrinsic sources of variation in size at birth and rates of postnatal growth in the big brown bat Eptesicus fuscus (Chiroptera: Vespertilionidae)

AbstractWe examined the relationship between intrinsic and extrinsic variables and variation in size at birth and rates of postnatal growth in the big brown bat Eptesicus fuscus at maternity roosts in central Massachusetts and southern New Hampshire. Body mass and length of forearm at birth were lowest when precipitation in the month preceding births was relatively high. In addition, body mass at birth was significantly lower when ambient temperatures during late pregnancy were relatively low. Pups born to middle age mothers were heavier than pups born to young or old mothers. When evaluated using mark–recapture data (longitudinal method), postnatal growth in length of forearm and body mass was greater for pups born to middle age and older mothers and change in body mass was greater for female pups than for male pups. When growth data were evaluated using the trajectory method, the rate of growth for length of forearm was greatest when ambient temperature was highest. Age prediction equations were improved when maternal age was incorporated into predictive equations. We recommend considering both intrinsic and extrinsic variables in studies where maternal effort is evaluated and age prediction equations are used for estimating postnatal growth rates in free‐ranging bats.

Intraspecific Variation in Postnatal Growth in the Greater Spear-Nosed Bat

Intraspecific variation in size at birth, postnatal growth, and survivorship of young mammals may reflect genetic variation, differential investment of mothers, gender of offspring, and environmental factors. We quantified size at birth and postnatal growth in free-ranging Phyllostomus hastatus (Chiroptera: Phyllostomidae) to develop age-predictive equations and examine effects of maternal size and age on size at birth and survivorship of young. There was a positive relationship between body mass of mothers and young; however, we found no relationship between maternal length of forearm or age on size of young at birth or survivorship. Males weighed more than females at birth and gained mass at a faster rate, although we found no significant gender differences at birth in length of forearm or length of total epiphyseal gap. High variation in size at birth and maturity suggests that there may be few environmental or life-history constraints on body size and postnatal growth in P. hastatus.

Postnatal Growth and Development in the Mexican Free-Tailed Bat (Tadarida brasiliensis mexicana): Birth Size, Growth Rates, and Age Estimation

Based on mark-recapture data, we quantified changes in body mass, length of forearm, and lengths of the total, proximal, and distal epiphyseal gaps of individual Mexican free-tailed bats (Tadarida brasiliensis mexicana) from birth to peak lactation. We used these data to develop empirical growth curves, derive growth rates, establish age-predictive equations, and compare growth parameters based on three nonlinear growth models. Length of forearm and body mass of neonates averaged 18.5 mm ? 0.7 (SD) and 3.2 g + 0.3, respectively. Mean body mass of pups increased linearly for the first 3 weeks, by which time they had achieved ca. 80% of the mean postpartum mass of adult females. Thereafter, body mass remained relatively stable until a small decrease in body mass was observed at the beginning of the 6th week when young first began to fly. The growth trajectory of the forearm also was linear for the first 3 weeks, but, thereafter, increased more slowly until average adult dimensions were reached in the 6th week. Length of total epiphyseal gap increased to its maximum size during the first 2 weeks and subsequently decreased in a linear fashion. Secondary centers of ossification appeared in the metacarpal and first phalanx of the fourth digit at ca. 14 days, thus, making it possible to quantify age-related changes in the proximal and distal epiphyseal gaps. The equation for estimating age based on length of the forearm is valid when this dimension is -39 mm, whereas the equation for estimating age based on length of the total epiphyseal gap is valid when length of the forearm is >39 mm. Together, these two equations make it possible to estimate the age of pups from 1 to 42 days of age in T. brasiliensis. Of the three nonlinear growth models (logistic, Gompertz, and von Bertalanffy), the logistic equation provides the best fit to the empirical curves for length of forearm and body mass.

Estimation of the developmental age of the bovine fetus and newborn calf.

Jersey cows from several herds provided 97 fetuses and 24 calves at fixed gestational intervals between 80 and 290 days after conception. The fetuses and calves were killed, weighed and measured and, after dissection, the sizes and weights of a range of skeletal and soft tissues were recorded. Six morphological measurements emerged as most suitable for the determination of developmental age in the normal fetus. By plotting their mean values and 95 per cent tolerance limits, the rates of growth and the variability of each measurement were defined. Long bone length was the most useful single measurement for predicting the developmental age of the fetus. Brain weight, bodyweight, crown-anus length and long bone length showed curvilinear growth patterns; age prediction equations derived from these measurements are complicated to use and additional simplified formulae have been derived. The number of appendicular ossification centres also had predictive value, but it could not be used to determine fetal developmental age between 100 and 160 days gestation.

Stem-Diameter Age Relationships of Tamarix ramosissima in Central Utah

The stem-diameter age relationships of salt cedar from 15 study sites in central Utah were investigated. Age prediction equations were generated and found significant (p<.OOl). Within restricted geographic areas the stem ages of salt cedar could be estimated with fair reliability, but with substantial geographic separation results were less accurate. The impact of salt cedar invasion over prolonged periods of time was also assessed. Results indicated that the longer the community has been occupied by salt cedar the more xeric the habitat becomes. Saltcedar (Tamarix ramosissima) is a vigorous invader of pastures, moist lowlands and stream banks throughout much of the southwestern United States (Tomanek and Ziegler 1960). It is also found in dense thickets through much of central Utah (Christensen 1962). Saltcedar has the highest transpiration rates of any North American phreatophyte (Kiegler 1968) and can depress the water table often by as much as 1.2 to 2.1 m/ yr (Horton 1964). Although studies have been made of the distribution and naturalization of saltcedar (Christensen 1962, and Horton 1964), and of its ecology and habitat requirements (Tomanek and Ziegler 1960, Carman 1979), much less is known of its stem diameter: age relationship and/or population dynamics. Studies of the growth rings of trees have been used extensively for dating (Douglas 1935, Glock 1937) reconstructing past climates (Fruits 1971, Harper 1979, Schulman 1956, Stockton and Meko 1975) and interpretation of successional dynamics (Burkhardt and Tisdale 1969, Barney 1972). Data on shrubs are relatively rare (Ferguson 1958, 1959; Ferguson and Humphrey 1959) but should be equally valuable. Brotherson et al. (1980b) included saltcedar in their study of the size and age relations of 8 major tree species of Navajo National Monument, Ariz. The present study considers the stem diameterage relationship of saltcedar from 15 sites in central Utah and compares these relationships with the Arizona saltcedar population.

Population Dynamics and Age Relationships of 8 Tree Species in Navajo National Monument, Arizona

The presence of 3 major archeological ruins dating from the I lth to 13th centuries (Woodbury 1963) provided the primary motivation for including Navajo National Monument in the National Parks System. Also included in the monument are some unique ecosystems, especially a small relict of mountain vegetation found in Betatakin Canyon. As visitor pressures mount annually, proper management of these unique ecosystems becomes highly important. Since trees are the dominant features of these ecosystems, and are central to management considerations, the present work has examined populations of 8 major tree species in the monument. The objectives of this study were, first, to develop age prediction equations for tree species growing in Navajo National Monument, and second, to assess the present age profiles, reproductive recruitment, and density relationships of these tree populations. Variations in the growth-ring widths of trees have been used for many years to date wood (Douglas 1935, Glock 1937) and to garner information on past climates (Fritts 1971; Stockton and Meko 1975; Dean and Robinson 1978; Harper 1979). Additionally, ring width variations have been studied to ascertain differences in the environments of selected habitats (Ferguson and Humphrey 1959, Stockton and Fritts 1973, Fritts 1974) and to assess site quality with reference to timber production (State 1966, Brickell 1968, Jones 1969). Although stem diameter measuresments have long been used to predict tree age and ascertain population status, it is difficult to use data from one area to extrapolate to conditions in other areas (Dealy 1975, Brotherson et al. 1980). Because of these difficulties and because of the absence of such data on northeastern Arizona plant communities, our studies provide useful baseline information.