Distribution Of Birth Dates Research Articles

Medulloblastoma and Birth Date: Evaluation of 3 U.S. Datasets

Studies from Norway and Japan have found a higher incidence of medulloblastoma related to births that occur in the fall. The authors sought further evidence concerning this association. For 122 patients in a Duke University database and 90 patients from the Central Cancer Registry of North Carolina, the frequency distribution of birth dates by month was statistically significantly different from the expected North Carolina distribution (p = 0.04 and 0.06). For 75 patients from California Surveillance, Epidemiology, and End Results (SEER) data, the frequency distribution of birth dates by month was marginally different from the expected U.S. distribution (p = 0.14). For 922 patients from national SEER data, the frequency distribution of birth dates by month was not statistically significantly different from the expected U.S. distribution (p = 0.54). Subgroup analysis suggests seasonality of birth dates is most significant for patients aged 5-14 yr diagnosed with medulloblastoma.

Environmental and stock effects on spawning origins and recruitment of cod Gadus morhua

Recent studies modelling back-calculated birth date distributions of pelagic juvenile (0-group) cod Gadus morhua have indicated differential regional spawning components in waters off the west, north and east coasts of Iceland, in contrast to traditional paradigms of stock structure. The relative proportions of pelagic juvenile cod that were estimated to originate from these regional spawning components were hypothesized to influence recruitment and vary in response to the inflow of Atlantic water from the main spawning grounds off the southwest coast to the main nursery grounds off the north coast. We examine this hypothesis by analyzing annual (1971 to 1998) coastal current data in relation to the total relative abundance, mean total length, and proportions of pelagic juvenile cod that were estimated to originate from the main spawning component off the southwest coast of Iceland. Additional variation in environmental (temperature, salinity, and zooplankton bio- mass) and spawning stock biomass (SSB) effects were also examined in relation to the 0-group vari- ables and recruitment at Age 3 to enable a detailed analysis of the stock-recruitment relationship. The coastal current index was the most dominant covariate affecting the spawning origins and recruitment of cod in Icelandic waters. The freshwater-induced coastal current provided a pre- dictable transport mechanism for pelagic eggs and larvae derived from the main spawning compo- nent off the southwest coast to the main nursery grounds off the north coast. In years when the coastal current were strong, more abundant and larger pelagic juveniles derived from the main spawning component were found on the main nursery grounds, typically resulting in corresponding years of good recruitment. Differentiating the interplay of the physical environment with that of a spawning stock is fundamental to understanding recruitment variability in marine fish stocks.

Accuracy of Recorded Birth and Calving Dates of Dairy Cattle in the United States

Frequencies of births that were reported for specific days of the month were documented for US dairy cattle born since 1987 by birth year, herd size, and registry status and compared with calving frequencies for those dates. Because birth dates are expected to be random and uniformly distributed throughout each month, percentages of births on individual dates were expected to be equal (3.3% for d 1 to d 28, 3.2% for d 29, 3.0% for d 30, and 1.9% for d 31). However, percentages of reported birth dates for d 1, 2, 10, 15, and 20 were higher than expected. The percentage of reported births for d 1 was highest (5.3%) of all days of the month regardless of herd size or registry status. The nonuniform distribution of birth dates within month indicated that a substantial number of birth dates were unknown and that estimated birth dates had been reported. About one-third of the birth dates recorded on d 1 appeared to have been estimated, or altered to gain an advantage in cattle shows. The highest frequencies for birth dates on d 1 (5.9 to 7.4%) were found for registered cows during months that initiated age groupings for dairy shows (March, June, September, and December). Birth dates for some registered cows were intentionally misreported as confirmed by comparison of birth dates of individual cows with calving dates of their dams. Reported calving dates appeared to be more accurate than reported births; the inflated frequency of recorded calvings on d 1 was only about 30% as large as the inflated frequency of recorded births. Because cow age is determined by birth date, proper reporting of birth dates is important to ensure the accuracy of standardized yield and fitness records and the genetic evaluations that are based on those records. When animals’ recorded birth dates and their dams’ calving dates differ, more credence should be given to the latter to improve accuracy.

Unequal Competition as an Impediment to Personal Development: A Review of the Relative Age Effect in Sport

Children born shortly before the cutoff date for age grouping in youth sport programs suffer from being promoted to higher age groups earlier than their later-born peers. Skewed birthdate distributions among participants in youth sport and professional sport leagues have been interpreted as the result of this disadvantage. A growing body of research shows that this Relative Age Effect in sport is a worldwide phenomenon and that it exists in many, but not all, competitive sports. Both physical and psychological mechanisms that may be responsible for the effect are identified. Negative consequences on personal development and possible remedies to the problem are discussed. Finally, desirable and necessary directions for future research are formulated.

Is There an Epidemic of Autism?

The debate on the hypothesis of a secular increase in rates of autism would benefit from a clear recognition of the methodologic limitations of existing data. No psychiatric case register study has ever allowed for estimating and monitoring the incidence of autistic conditions over time.1Cross-sectional surveys hugely differ in their case definition and case identification methods that account for large variations in prevalence estimates both over time and across areas, precluding a meaningful analysis of time trends. That rates in recent surveys are substantially higher than 30 years ago merely reflects the adoption of a much broader concept of autism, a recognition of autism among normally intelligent subjects, changes in diagnostic criteria, and an improved identification of persons with autism attributable to better services.1,2 The only epidemiologic study where case definition and identification could be held constant failed to detect an increase in rates of autism in successive birth cohorts from 1972 to 1985.3 Most of the claims about the ‘epidemic’ of autism are therefore based on referral statistics from various centers. The report of the Department of Developmental Services from California has been, and still is, widely quoted as evidence for an epidemic of autism.4 The key data of this report (Table 1 and Fig 1) need a critical examination. View this table: Table 1. Autism and Other PDDs Registered in California (1987–1998) Fig. 1. Distribution of birth dates of regional center eligible persons with autism (California). First, the figures apply to numbers rather than …

Mean arterial pressure, pregnancy induced hypertension, and preeclampsia: Evaluation as independent risk factors and as surrogates for high maternal serum alpha-protein in estimating breast cancer risk.

PURPOSE: Data from a nested case-control study were analyzed to examine high mean arterial pressure (MAP), hypertension of pregnancy and preeclampsia as independent predictors, and as surrogate markers for elevated Alpha-fetoprotein (AFP) levels in evaluating breast cancer risk.METHODS: Cases (n = 205) were identified by the California Cancer Registry from a cohort of pregnant women who were part of the Kaiser Health Plan and took part in the Child Health and Development Studies initiated by the University of California, Berkeley, from June 1959 to September 1966. Controls (n = 337) were selected by randomized recruitment from the same cohort probability matched to cases by distribution of birth dates of cases.RESULTS: High MAP was associated with breast cancer risk, and was different across quartiles of age at first full term pregnancy. Odds Ratios across quartiles were 0.24 (95% CI = 0.08–0.71), 0.84 (95% CI = 0.39–1.66), 1.00 (referent), and 2.50 (95% CI = 1.21–5.13). Neither diagnosed preeclampsia nor hypertension of pregnancy showed any association with breast cancer risk. When both high Alpha-fetoprotein and high mean arterial pressure were entered into the same analysis neither changed the odds ratio for the other more than eight percent. Additionally, AFP level was not a linear function of MAP.CONCLUSIONS: Although the pattern of odds ratios across quartiles of age at first full term pregnancy were similar for the two variables it can not be concluded that high MAP is an adequate surrogate for high levels of maternal serum AFP, but rather represents some related process which is in and of itself a risk factor for breast cancer.

Growth and hatching dates of juvenile pacific sardine Sardinops caeruleus in the Gulf of California

The otolith microstructure of juvenile Pacific sardine, Sardinops caeruleus, was examined to estimate age, growth, and back-calculated hatching-date distributions. Hatching-date distributions were corrected to mortality. Juveniles were collected from the Gulf of California during February 1995, January–February and June 1996. Estimated ages of juveniles ranged from 43 to 158 days (26–105 mm SL). A Gompertz growth model provided a good description ( r 2=0.77) of the length-at-age relationship. The maximum calculated daily growth rate was 0.71 mm per day for 74-day-old fish. The average growth rate up to 160-days-old was 0.64 mm per day. The back-calculated hatching-date distributions showed that spawning occurs from October to April. The average birthdate distributions correspond to the beginning of the productivity cycle and consequently the growth was not limited by feeding conditions during 1995 and 1996.

Effect of a change in selection year on success in male soccer players.

Since 1997 and following the guidelines of the International Football Association, the Belgian Soccer Federation has used January 1st as the start of the selection year. Previously, August 1 was the start. This shift prompted an investigation of changes in birth-date distributions throughout youth categories for 1996-1997 compared to the 1997-1998 competitive years. Birth dates were considered for national youth league players, ages 10-12, 12-14, 14-16, and 16-18 years. Kolmogorov Smirnov tests assessed differences between observed and expected birth-date distributions. Regression analyses examined the relationship between month of birth and number of participants both before and after the August to January shift. Results indicated that from 1996 to 1997, youth players born from January to March (the early part of the new selection year) were more likely to be identified as "talented" and to be exposed to higher levels of coaching. In comparison, players born late in the new selection year (August to October) were assessed as "talented" in significantly lower proportions. Specific suggestions are presented to reduce the relative age effect. Am. J. Hum. Biol. 12:729-735, 2000. Copyright 2000 Wiley-Liss, Inc.

Season of Birth in Panic Disorder

Several studies have investigated the seasonal distribution of the birth dates of patients with psychiatric diseases. Our purpose was to verify if there is a specific distribution (by month) of birth dates in subjects with panic disorder (PD). The birth dates of 843 outpatients with a diagnosis of PD were compared with those of 1,181 subjects with other mental diseases. The birth dates of psychiatric patients were compared to those of the general Tuscane and Italian populations. The monthly distribution of birth in patients with PD (with and without comorbidity) peaked in September to December, while no relevant deviation in birth rate was observed in other mental diseases. Our results suggest a pathogenic role of birth seasonality in the development of PD.

Carbon content and nutritional condition of sardine larvae ( Sardina pilchardus ) off the Atlantic coast of Spain

As part of a “European Sardine/Anchovy Recruitment Program” (SARP), sardine larvae (Sardina pilchardus) were sampled off the Atlantic coast of Spain through the spawning season from March to June. The larvae were analysed for carbon and nitrogen content as a measure of nutritional condition and survival potential. There was no significant diel variation in larval carbon content, but there was a small significant diel variation in nitrogen; the absence of a strong diel signal in elemental composition was ascribed to the overnight retention of the gut contents. There was an increase in carbon content with increase in body length which reached an asymptote at ∼40% carbon content at a larval length of 20 mm. It is argued that larvae with a carbon content of <25% of body weight were nutritionally stressed, with the smaller larvae (<10 mm in length) appearing to be more vulnerable to food limitation. Although larvae with the lowest age-specific carbon content (poorest condition) occurred on the cruise with the lowest food availability, there was no consistent relationship between carbon content and food availability. While the successive monthly estimates of carbon content revealed differences in potential recruitment between months, these were not related to the birth-date distribution of the surviving juveniles.

The Relative Age Effect in Soccer: Cross-Cultural Evidence for a Systematic Discrimination against Children Born Late in the Competition Year

Previous findings of skewed birth date distributions among sports professionals have been interpreted as evidence for a systematic discrimination against children born shortly before the cut-off date for each age grouping. Alternative explanations for these findings exist, however. This research therefore attempted to replicate the effect in a cross-cultural comparison. A strong relative age effect in professional soccer was found in Germany, Japan, Brazil, and Australia, showing that the effect is independent of different cut-off dates and a variety of climatic and sociocultural factors. A shifted peak in the birth date distribution of Australian soccer professionals paralleling a corresponding change in the cut-off date in Australian soccer in 1989 was also established. This pattern of results provides strong evidence for the cut-off date in youth soccer as the main cause for the relative age effect in professional soccer.

The influence of relative age on success and dropout in male soccer players.

The consistent asymmetry in the birth-date distribution of senior professional soccer players has led us to investigate whether similar asymmetries emerge throughout youth categories in soccer. Birth dates were considered for professional players, national youth teams, youth players transferred to top teams, and regular youth league players. Kolmogorov Smirnov tests assessed differences between observed and expected birth-date distributions. Regression analyses examined the relationship between month of birth and number of participants at various levels of play in soccer. Results indicated that youth players born from August to October (the early part of the selection year), beginning in the 6-8 year age group, are more likely to be identified as talented and to be exposed to higher levels of coaching. Eventually, these players are more likely to be transferred to top teams, to play for national teams, and to become involved professionally. In comparison, players born late in the selection year tended to dropout as early as 12 years of age. Recommendations suggest a review of the 24-month age band and current methods for talent detection and selection. Am. J. Hum. Biol. 10:791-798, 1998. © 1998 Wiley-Liss, Inc.

Use of a stochastic model of a calving distribution for beef cows for formulating optimal natural mating strategies

AbstractA model of a birthdate distribution for a herd of beef cows is constructed using the probability distributions of the variables that affect reproduction in the cow — anoestrous interval, oestrous cycle length, conception to each oestrus, gestation length, period of mating and the prior calving frequency distribution. The model is general and can be reparamaterized to deal with issues such as intervention to synchronize oestrous cycles among cows in the herd by changing the form of the relevant probability distributions.The model is applied to the question of what time to begin mating in a herd of beef cows. The average calf live weight at day 200, herd conception rate and proportion of cows calving before the planned start of calving were calculated from the model output. The model parameters given by the anoestrous period, conception rate to each oestrus and the regression between prior calving date and anoestrous period, were varied in a factorial design to investigate a range of circumstances found on a farm. Prior calving distributions were generated by random sampling from eight actual calving frequency distributions.Generally starling mating earlier produced an advantage in terms of extra calf live weight and herd conception rate. However, the proportion of the herd calving earlier than expected increased with early mating. Thus, the feasibility of early mating depends on the cost to the farmer of dealing with early calving cows as well as the advantage of heavier older calves.Altering the fixed parameters in the model (variances and covariances, prior calving distributions, mating period) to accommodate the circumstances of herds run under different conditions may produce different results. Model structure allows easy alteration of these parameters and also the introduction of different probability distributions for some variables. This might be necessary to model oestrous synchronization and artificial insemination, issues not considered in this paper.

Monthly distribution of multiple sclerosis patients' births.

As part of an integrated geographical and environmental epidemiological study of multiple sclerosis (MS) in Budapest's Pesterzsébet district, many biometeorological variables were specifically examined. Also, the monthly distribution of birthdates of MS patients resident in the district was plotted. Patients reliably diagnosed with MS were found to have been born in greater numbers in the months of April and October, precisely 6 months apart. This finding indicates the presence of natural non-genetic factors in the creation of MS susceptibility, affecting the nervous system at the crucial time of myelination.

Lack of evidence for seasonal variation in extrahepatic biliary atresia during infancy.

Biliary atresia has been reported anecdotally to occur with temporal and geographic clustering suggestive of an infectious etiology. We examined the birth dates of infants with extrahepatic biliary atresia (EHBA) during an 18-year period for evidence of a monthly or seasonal distribution. Sixty-five patients referred for biliary atresia to the University of Michigan over this period were used as index cases. The monthly and seasonal distributions of birth dates of patients with EHBA were compared by chi 2 analysis to the monthly and seasonal birth rates of infants born in Michigan (p < 0.77 and p < 0.91, respectively). No significant difference was identified. A power analysis showed that our study had an 80% probability of recognizing a 30% variation in birth rates grouped over a 3-month period. The monthly and seasonal distributions of conception dates of patients with EHBA were also compared and found not to be significantly different from the conception dates of infants born in Michigan. We conclude that there is no monthly or seasonal variation in the date of birth or the date of conception of infants with biliary atresia.

Lack of a Season of Birth Effect among American Athletes

Previous studies have reported uneven distributions of birth dates across the year for European athletes in several sports. The usual explanation has been that being born in a particular part of the year confers selective advantages or disadvantages depending on what part of the year the season of the sport in question begins. We now report the first study of season of birth effects in American athletes. We found no such effect in a sample of 167 highly skilled football players or in a sample of 600 baseball players.

Distribution and abundance of post-larvae and juveniles of the Patagonian sprat, Sprattus fuegensis, and related hydrographic conditions

This paper reports on the first pelagic survey on the southern Patagonian shelf. As a result of a joint Argentine-Russian cruise on board the R/V ‘Dmitry Stefanov’ carried out in the early autumn of 1992, a major nursery ground of Sprattus fuegensis was located in the coastal area off Santa Cruz and Tierra del Fuego. Forty-nine ichthyoplankton stations along 14 transects and seven intertransects were occupied. Biological samples were taken with an Isaacs-Kidd midwater trawl (IKMT) equipped with a net sounder and flowmeter. Hydrological data were obtained at 78 conductivity-temperature-depth sensor (CTD) stations. Meteorological observations were made concurrently. Real-time sea surface temperature (SST) images from NOAA satellites were received on board, twice per day, cloud permitting. Positive stations lay mostly within the 50 m depth contour. Of all coastal stations 71% were positive for sprat post-larvae and juveniles. The density and size of the specimens collected increased southwards. Median values of the juvenile distribution varied from 23.6 mm standard length (SL) to the north of the study region to 38.5 mm for stations at 54 °S. Highest biomass densities (> 2.8 t per square nautical mile) were found to the south of the Magellan Strait, corresponding to IKMT densities of over 1000 specimens per haul. Other important components of the Isaacs-Kidd collections were the post-larval and juvenile stages of Sebastes oculatus and Patagonotothen tessellata. To obtain a higher resolution view of the distribution and abundance of juvenile sprat, the area was simultaneously surveyed using an EK-400 echosounder with a SIORS echointegrator. The acoustically derived sprat densities were higher than those obtained from IKMT sampling; however, a significant correlation ( r = 0.98; α < 0.01) was obtained between IKMT and echointegration data. The large amount of post-larvae and juveniles collected and the very high values of echointegration registered, particularly in the area of the strait and channels, are indicative of a major nursery ground of the species along the Patagonian coast. Juvenile production in the area was estimated at 1.32 × 10 9 individuals. Differences in the diel patterns of the vertical migration of adult and early juveniles are described. Growth increments in otoliths were used to estimate the age of sprat post-larvae and juveniles. A Laird-Gompertz model was fitted to the length-at-age data. The spawning periodicity of the species was determined by examining the temporal distribution of birth dates from otolith-aged specimens. There was an indication of a major spawning peak in late December, and a secondary one in mid-January. Available information on the reproduction and early life history of the species is analysed in relation to the obtained results. The importance of the low-salinity water outflow in the Magellan Strait for egg dispersal and larval retention is discussed.

Biological and oceanographic insights from larval labrid (Pisces: Labridae) identification using mtDNA sequences

Polymerase chain reaction and direct comparison of mitochondrial DNA sequences from a cytochrome b gene fragment were used to identify two morphologically distinct larval types ofXyrichtys, a genus of tropical wrasse (Pisces: Labridae). Both larval types were collected during ichthyoplankton surveys on the Middle Atlantic Bight shelf in the summer of 1988. DNA sequence comparisons indicated that both types were larvae ofXyrichtys novacula (Linnaeus). Back-calculated birthdate distributions for those larvae collected on the Middle Atlantic Bight shelf demonstrated that the two larval types formed two distinct cohorts indicating a biological difference. The two distinct larval types may be a consequence of an ecophenotypic effect, or they may represent offspring from genetically distinct populations. These results emphasize that important biological and oceanographic information can be gained through the use of the polymerase chain reaction and DNA sequencing for larval identificaiton.

Age, growth and back-calculated birthdate distributions of larval jack mackerel, Trachurus declivis (Pisces: Carangidae), from eastern Tasmanian coastal waters

Otolith microstructure of the larvae of jack mackerel, Trachurus declivis, was examined to derive estimates of age, growth and back-calculated birthdate distributions. Larvae were collected from shelf waters of the eastern coast of Tasmania between January and March, 1989 to 1991. Daily increment formation was confirmed by successive sampling of a cohort of individuals, correlating the change in the number of increments with the sampling interval. Otoliths examined under the scanning electron microscope confirmed the otolith structure and increment counts obtained with the light microscope. Initial increments were shown to form at the time of first feeding. Estimated ages of larvae ranged from 2 to 25 days after first feeding, and larvae showed exponential growth in all three years. Interannual variations in larval growth were evident, with growth being significantly slower in 1991 (4.6% of standard length per day) than in 1989 (5.2% SL day-1) and 1990 (5.4% SL day-1). The faster growth in 1989 and 1990 may be attributable to warmer-than-normal water temperatures over the study area in these years associated with a major La Nina event. Back-calculated birthdate distributions showed that spawning occurred during summer (mid December to mid February) in all three years, with indications of semilunar spawning activity in which peaks were apparently associated with both full and new moons.

Epidemiological Evidence that Maternal Influenza Contributes to the Aetiology of Schizophrenia

The epidemiological evidence that the offspring of women exposed to influenza in pregnancy are at increased risk of schizophrenia is conflicting. In an attempt to clarify the issue we explored the relationship between the monthly incidence of influenza (and measles) in the general population and the distribution of birth dates of three large series of schizophrenia patients--16,960 Scottish patients born in 1932-60; 22,021 English patients born in 1921-60; and 18,723 Danish patients born in 1911-65. Exposure to the 1957 epidemic of A2 influenza in midpregnancy was associated with an increased incidence of schizophrenia, at least in females, in all three data sets. We also confirmed the previous report of a statistically significant long-term relationship between patients' birth dates and outbreaks of influenza in the English series, with time lags of -2 and -3 months (the sixth and seventh months of pregnancy). Despite several other negative studies by ourselves and others we conclude that these relationships are probably both genuine and causal; and that maternal influenza during the middle third of intrauterine development, or something closely associated with it, is implicated in the aetiology of some cases of schizophrenia.