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PubMed1994

Craniometric variation, genetic theory, and modern human origins.

Recent controversies surrounding models of modern human origins have focused on among-group variation, particularly the reconstruction of phylogenetic trees from mitochondrial DNA (mtDNA) and the dating of population divergence. Problems in tree estimation have been seen as weakening the case for a replacement model and favoring a multiregional evolution model. There has been less discussion of patterns of within-group variation, although the mtDNA evidence has consistently shown the greatest diversity within African populations. Problems of interpretation abound given the numerous factors that can influence within-group variation, including the possibility of earlier divergence, differences in population size, patterns of population expansion, and variation in migration rates. We present a model of within-group phenotypic variation and apply it to a large set of craniometric data representing major Old World geographic regions (57 measurements for 1,159 cases in four regions: Europe, Sub-Saharan Africa, Australasia, and the Far East). The model predicts a linear relationship between variation within populations (the average within-group variance) and variation between populations (the genetic distance of populations to pooled phenotypic means). On a global level this relationship should hold if the long-term effective population sizes of each region are correctly specified. Other potential effects on within-group variation are accounted for by the model. Comparison of observed and expected variances under the assumption of equal effective sizes for four regions indicates significantly greater within-group variation in Africa and significantly less within-group variation in Europe. These results suggest that the long-term effective population size was greatest in Africa. Closer examination of the model suggests that the long-term African effective size was roughly three times that of any other geographic region. Using these estimates of relative population size, we present a method for analyzing ancient population structure, which provides estimates of ancient migration. This method allows us to reconstruct migration history between geographic regions after adjustment for the effect of genetic drift on interpopulational distances. Our results show a clear isolation of Africa from other regions. We then present a method that allows direct estimation of the ancient migration matrix, thus providing us with information on the actual extent of interregional migration. These methods also provide estimates of time frames necessary to reach genetic equilibrium. The ultimate goal is extracting as much information from present-day patterns of human variation relevant to issues of human origins.(ABSTRACT TRUNCATED AT 400 WORDS)

Africa↗

PubMed1978

[Anatomy, variations and malformations of the vessels of the head and neck region (author's transl)].

After a short review of developmental data concerning the head and neck arteries, the normal conditions, variations and malformations of single arteries are described. Special attention is paied to the skeletotopic and topographic relations of the arteries. In every bigger vessel its length, position, origin and branches are described, and in most cases are also demonstrated by diagrams and tables. As the aortic arch may also reach the neck region, its variation and malformations as well as the variations of its branches are mentioned. The variations and the malformations of the inominate artery, of the common carotid artery, as well as of the external and internal carotid arteries are described. The practical importance of these variations is stressed. Upon description of variations and malformations anatomical, surgical und roentgenological findings described in literature, as well as personal experiences are considered. Special attention has been paied to the variations of the circulus arteriosus Willisi, to the persistence of the presegmental arteries and to the possibility of formation of a by-pass in occlusion or aplasia of cerebral arteries. The position of the subclavian artery, its variations and the variations of its branches are described. After a short embryological introduction, the variations of the venous system and its anastomoses are described. At the end, the main variations of the big lymphatic vessels in the neck are mentioned.

Aorta, Thoracic↗

PubMed1996

The effect of urethral pressure variation on detrusor activity in women.

The purposes of this study were to confirm previously described patterns of urethral pressure variation and to establish criteria for their diagnosis. The effect of urethral pressure variation on detrusor activity was also examined. The study involved a retrospective review of the computerized cystometric tracings from a 26-month period. Forty-one patients had artefact-free satisfactory tracings demonstrating urethral pressure variation, detrusor instability and/or gradual detrusor pressure increase. These tracings were stored on a computer program which permitted real-time second-by-second review. Statistical analysis was done using Fisher's exact test and an independent t-test. Three patterns of urethral pressure variation were identified: rapid pressure variation (RPV), gradual pressure variation (GPV) and stress-induced transient urethral relaxation (SITUR). RPV was associated with onset at low bladder volumes (independent t-test, P = 0.02) and with detrusor instability (Fisher's exact test, P < 0.001). GPV began at high bladder volumes (Fisher's exact test, P < 0.001). SITUR was not associated with any specific pattern of urethral pressure variation or detrusor pressure change. Analysis of tracings of the patients with a combination of rapid urethral pressure variation and detrusor instability revealed a statistically significant increased frequency of urethral relaxation as the primary event precipitating an unstable detrusor contraction (Fisher's exact test, P < 0.003). In conclusion, three different patterns of urethral pressure variation were identified. Rapid pattern of urethral pressure variation is closely associated with detrusor instability. Further study of urethral pressure variation may help to elucidate the pathophysiologic mechanism responsible for idiopathic unstable detrusor contractions.

Adult↗

PubMed2005

Within-plant variation in glucosinolate concentrations of Raphanus sativus across multiple scales.

Variation in chemical defenses remains underexplored. In particular, little is known about patterns of variation at small scales within leaves and spatial variation of induction. I examined variation in glucosinolate concentrations in the leaves of Raphanus sativus at several different spatial scales in two related experiments. I used samples equivalent in area to the amount an intermediate-sized caterpillar might eat in 1 d, a smaller scale than used in most previous studies. I examined variation due to induction and leaf age and small-scale spatial variation within leaves. The mean and variance of glucosinolate concentrations were higher in induced plants, young leaves, and the proximal half of leaves. Higher glucosinolate concentrations in the proximal half of leaves are previously unreported. Small-scale variation was extreme, accounting for 57% of the total random variation, and spatially random. There was no spatial autocorrelation found at scales as small as 1-2 cm. The high degree of small-scale, spatially random variation in glucosinolate concentrations in leaves is previously unreported. This small-scale variation and the variation caused by induction may have significant effects on herbivores and could be an important component of plant defense.

Glucosinolates↗

PubMed1989

Serotonin S2 and thromboxane A2-prostaglandin H2 receptor blockade provide protection against epinephrine-induced cyclic flow variations in severely narrowed canine coronary arteries.

The object of this study was to test the hypothesis that administration of both serotonin S2 and thromboxane A2-prostaglandin H2 (PGH2) receptor antagonists provides significant protection against epinephrine-induced cyclic coronary artery flow variations in open chest, anesthetized dogs with severe proximal coronary artery stenosis and endothelial injury. Three groups of dogs were studied. In Group 1 (n = 7) and Group 2 (n = 6), cyclic coronary flow variations were initiated after placement of a concentric constrictor around the left anterior descending coronary artery and were abolished by administration of either a thromboxane A2-prostaglandin H2 receptor antagonist, SQ29,548 (SQ) (Group 1), or a serotonin S2 receptor antagonist, LY53,857 (LY) (Group 2). Cyclic flow variations were restored with an epinephrine infusion and the second antagonist (LY for Group 1; SQ for Group 2) was administered to abolish epinephrine-induced cyclic flow variations. The rate of epinephrine infusion was increased until cyclic coronary flow variations returned (n = 8) or significant hemodynamic changes occurred. Plasma epinephrine concentrations were determined during a control period of cyclic coronary flow variations, after epinephrine restored cyclic flow variations in the presence of either SQ or LY, and again after epinephrine restored cyclic flow variations in the presence of both SQ and LY. A third group of dogs (Group 3, n = 9) required both SQ and LY to eliminate the initial cyclic coronary flow variations and infused epinephrine restored cyclic flow variations (n = 8). Plasma epinephrine concentrations were determined during a control period and after cyclic coronary flow variation restoration with epinephrine.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1984

Sources of interindividual variations in acetaminophen and antipyrine metabolism.

Our goal was to compare and contrast in the same normal twins the relative contribution of genetic and environmental factors to large interindividual variations in the metabolism of acetaminophen (APAP) and antipyrine. These drugs were selected because they are biotransformed by different mechanisms. A single oral dose of APAP (10 mg/kg) was given to six sets of monozygotic (MZ) and six sets of dizygotic (DZ) twins. All were normal, nonsmoking, nonmedicated, and male. Among these 24 subjects, there were 300% interindividual variations in rate constants for formation of the sulfate and glucuronide conjugates, as well as in the overall rate constant for APAP elimination. Intratwin variations for each measurement were as large within MZ as within DZ twinships, suggesting that predominantly environmental rather than genetic factors maintained interindividual variations. Two other observations support this conclusion: Intraindividual variations were frequently as large as interindividual variations, and regardless of zygosity for twins living together, intratwin correlation coefficients were almost twice those of twins living apart. Quite different results were obtained when these twins received antipyrine. After a single oral dose of antipyrine (18 mg/kg), 500% interindividual variations in rate constants for formation of the three main oxidative metabolites of antipyrine appeared to be mainly under genetic control. Also for antipyrine and its principal metabolites, intraindividual variations were much smaller than interindividual variations. In contrast to the results with APAP, regardless of zygosity, intratwin correlation coefficients for antipyrine were similar for twins living apart and twins living together. This comparison between APAP and antipyrine metabolism in the same carefully selected normal twins under apparently uniform environmental conditions reveals that interindividual variations in APAP metabolism arise from certain unidentified environmental factors, whereas genetic factors cause the large interindividual variations that occur in antipyrine disposition.

Acetaminophen↗

PubMed1975

The effects of time of venipuncture on variation of serum constituents. Consideration of within-day and day-to-day changes in a group of healthy young men.

Within-day and the day-to-day variations of serum constituents were evaluated in 11 healthy young men. Eighteen constituents, including electrolytes, metabolites, proteins, and enzymes, were assayed using the AutoChemist MultiChannel Analytic System. Venipunctures were performed at three hours of the day, 8 A.M., 11 A.M., and 2 P.M., on five separate experimental days. A three-factor analysis of variance model was employed to separate analytic variation from biological sources of variation. Statistically significant (p less than .05) group diurnal patterns (main effect of hour) during the six-hour period were found for serum lipids, iron, urea, albumin, total protein, and chloride. A unique individual diurnal pattern (subject-hour interaction) was statistically significant for serum potassium. Statistically significant main effect of month (main effect of day) for the group of subjects was seen for total lipids and potassium; however, the subject-day interaction term, which is an index of the day-to-day variation for the subjects, was significant (p less than .05) for all of the constituents except for sodium ion. The comparison of the variation expected within-day versus the variation seen day-to-day over four months was made by pooling the sources of within-day variation (main effect of hour + subject-hour interaction + subject-day-hour interaction) and by pooling the day-to-day variation terms (main effect of day + subject-month interaction). For serum cholesterol, potassium, acid phosphatase, and phosphate ion, the within-day variation was greater than the day-to-day variation occurring over four months, while the other constituents showed day-to-day variations of a greater magnitude than that experienced during the six-hour period.

Acid Phosphatase↗

PubMed1978

Evaluation of biologic sources of variation of leukocyte counts and other hematologic quantities using very precise automated analyzers.

The authors determined mean day-to-day (daily over five days), mean week-to-week (weekly over five weeks) and mean hour-to-hour (800 h, 1100 h, 1400 h) physiologic intra-individual variation of concentration values of leukocyte cell types, platelet count, and erythrocyte values (hematocrit, hemoglobin) for a group of 20 healthy adult volunteers. Total leukocyte counts and concentration values of leukocyte cell types were determined in duplicate on the Hemalong-DTM Automated Leukocyte Differential Cell Counter to minimize analytic variation. The data sets were analyzed according to an analysis of variance model. The mean physiologic hour-to-hour and week-to-week intra-individual variations in terms of % coefficient of variation included: hemoglobin, 2.5, 2.2; hematocrit, 2.6, 2.7; platelets, 1.6, 6.6; total leukocyte count, 9.4, 15.7; neutrophils, 12.9, 26.0; lymphocytes, 10.3, 13.2; monocytes, 18.6, 19.3; eosinophils, 19.9, 26.9; basophils, 7.4, 15.0; large unstained cells, 13.7, 16.0; "high-peroxidase" cells, 32.7, 25.7. Hour-to-hour variation was partitioned into random diurnal variation, group-consistent diurnal variation, and subject-specific unique individual variation. Subject-specific diurnal variation contributed greatly and statistically significantly to total diurnal variation for many of the leukocyte cell types--especially in the case of eosinophils, where it represented more than half of total diurnal variation.

Adult↗

PubMed2006

Robustness of coalescent estimators to between-lineage mutation rate variation.

Data from HIV and from human neoplastic cells can show substantial between-lineage mutation rate variation even within a single population. Such variation may affect estimators of population quantities such as Theta = 4N(e)mu. Using simulated DNA data, I measured the effect of rate variation on recovery of Theta by the summary-statistic estimator of Watterson (Watterson GA. 1975. On the number of segregating sites in genetical systems without recombination. Theor Popul Biol. 7:256-276) and the coalescent maximum likelihood algorithm LAMARC (Kuhner MK. 2006. LAMARC 2.0: maximum likelihood and Bayesian estimation of population parameters. Bioinformatics. Advance Access doi: 10.1093/bioinformatics/btk051). Watterson's estimator showed a downward bias, as expected, with high values of Theta. LAMARC's mean estimate was accurate for all tested values of Theta and rate variation except for a downward bias when rate variation was maximal (i.e., the slow rate was zero). LAMARC had consistently narrower confidence intervals (CIs) than Watterson's estimator. Both methods tended to reject the truth too often when rate variation was 8x or greater and independent among branches, as well as when variation was 4x or greater and correlated among branches. In the case of Watterson's estimate, this excess rejection was fully attributable to variation among genealogies in the amount of total branch length associated with the fast and slow rates. However, in the case of LAMARC, some excess rejection was still observed even when between-genealogy variation was taken into account. Both estimators are robust to modest rate variation; however, their use should be coupled with a statistical test to rule out extreme rate variation as the resulting CIs may not be reliable.

Algorithms↗

PubMed1994

Geographical variation in hospital admission rates: an analysis of workload in the Oxford region, England.

OBJECTIVE: To measure variation in hospital admission rates between health districts in part of the English NHS, comparing a wide range of medical and surgical conditions. DESIGN: Retrospective analysis of interdistrict variation using linked routine hospital admission data. Comparisons were also made with levels of variation reported from the USA. SETTING: Oxford Regional Health Authority, 1979-86. SUBJECTS: Six district health authorities--total study population 2.1 million people, 1.6 million hospital admissions. MAIN MEASURES: Age and sex standardised hospital admission rates for resident populations for individual operations and diagnoses; systematic components of variation (SCV). RESULTS: Of 118 standard operation groups, 38 (26% of surgical workload) showed high variation (SCV 16 or more) and 40 (36% of surgical workload) showed low variation (SCV < 4). Operations (SCV) with very low levels of variation included prostatectomy (0.1), inguinal herniorraphy (0.9), and cholecystectomy (1.3). Rates were more variable for myringotomy (3.7), hysterectomy (4.3), dilatation and curettage (5.6), and tonsillectomy (6.2). The SCV was high for only four of the 40 commonest medical causes of admission, and was low for 18 of them. CONCLUSIONS: Most admissions in the Oxford region were for conditions that did not show a great deal of variation in admission rates. The level of variation for many surgical procedures was less than that reported in studies from the USA. Variation was no greater for medical causes of admission than for surgical conditions. Large scale variation may not be an inevitable consequence of autonomous clinical practice.

Age Factors↗

PubMed1998

Effect of the number of peak expiratory flow readings per day on the estimation of diurnal variation.

BACKGROUND: The number of peak expiratory flow (PEF) readings required per day to assess diurnal variation accurately is not known; published studies have used between two and seven PEF readings per day. This study compares the diurnal variation calculated using 2-10 PEF readings per day. METHODS: All days with 10 readings were selected from a database of PEF records. For each day, diurnal variations calculated using 2-9 of the readings available were compared with that calculated using the full 10 PEF readings. Diurnal variation calculated using all 10 readings was taken as the true diurnal variation. When less than 10 readings were used the readings were evenly spaced over waking hours. Diurnal variation was calculated as maximum--minimum/predicted. RESULTS: Two hundred and 25 days with 10 readings per day were selected from PEF records provided by 63 individuals. When only two PEF readings per day were used, the limits of agreement suggested a possible underestimate of true diurnal variation, calculated using all 10 readings, of 1.23-15.10%. The possible underestimate fell to 0.27-3.96% when calculated using four evenly spaced readings. Analysis of the timing of the highest PEF reading of the day was undertaken for rest and work days. This showed a mean (SD) timing of 13:56 (4:56 hours) for rest days and 11:47 (5:59 hours) for work days. CONCLUSIONS: Clinically significant underestimates of true diurnal variation may be seen when only small numbers of PEF readings per day are used in its calculation. At and above four readings the results suggest that the underestimate becomes increasingly insignificant in terms of the diagnosis and treatment of asthma. Analysis of the timing of the highest PEF reading of the day showed a wide variation, precluding the ability to capture the true diurnal variation with just two or three carefully timed PEF readings per day. The authors suggests that at least four readings per day should be performed, evenly spaced during waking hours, to obtain an accurate assessment of diurnal variation in PEF.

Adolescent↗

PubMed2003

Variation in levels of serum inhibin B, testosterone, estradiol, luteinizing hormone, follicle-stimulating hormone, and sex hormone-binding globulin in monthly samples from healthy men during a 17-month period: possible effects of seasons.

To obtain information on the scale of the intraindividual variation in testicular hormone, blood samples for inhibin B determination were collected monthly in 27 healthy male volunteers during a 17-month period. In addition, the traditional reproductive hormones FSH, LH, testosterone, estradiol, and SHBG were measured. The intraindividual variation in inhibin B over the study period was, on the average, 10%, corresponding to the assay variation of the inhibin B assay, indicating that most of the observed day to day variation in inhibin B levels in men could be explained by assay variation. A seasonal variation was observed in LH and testosterone levels, but not in the levels of the other hormones. The seasonal variation in testosterone levels could be explained by the variation in LH levels. The seasonal variation in LH levels seemed to be related to the mean air temperature during the month before blood sampling, but not to the length of daylight or the hours of sunshine. In conclusion, our data showed that day to day levels of inhibin B are relatively constant in men and do not seem to be influenced by seasonal factors. In contrast, we found a seasonal variation in LH and testosterone levels in men. The peak levels of both LH and testosterone were observed during June-July, with minimum levels present during winter-early spring. Air temperature, rather than light exposure, seems to be a possible climatic variable explaining the seasonal variation in LH levels.

Adult↗

PubMed2003

Haematocrit: within-subject and seasonal variation.

This review was undertaken, concerning within-subject biological variation and seasonal variation of haematocrit in normal healthy adults and athletes, to find the limits for natural, intra-individual variation in haematocrit values. The terminology and calculations followed well defined theories, from the field of laboratory medicine, about biological variation. Based on results from 12 studies of 638 normal healthy adults, and which used a sampling interval of 1 day to 1-2 months, the coefficient of within-subject biological variation of haematocrit is 3%. The normal within-subject biological variation (3%) and analytical variation (3%) may explain a relative change of approximately 12% (95% level) [e.g. a change from 0.42-0.47] between two successive haematocrit values, measured with a time interval between 1 day and 1-2 months, in a normal healthy adult. Partly due to haemodilution in warm weather, haematocrit often has a seasonal variation in normal healthy adults; based on results from 18 studies of 24 793 participants, the population mean is approximately 3% lower in summer than winter. Population mean values that are 7% lower in summer than winter have been found in some studies, although no seasonal effect may also be seen, especially in temperate climates. If haematocrit values are sampled at yearly peak and trough time points, with intervals of up to 6 months, a 15% relative change (95% level) can be seen in a normal healthy adult; e.g. a change from 0.42-0.48. Published values for haematocrit in athletes are scarce. It is known that the haematocrit value is influenced by training, especially in the first weeks before a new steady-state is reached. Theoretically, the biological variation in athletes could therefore be greater than in normal individuals. Based on two references addressing the biological variation of haematocrit in athletes, however, the above results are also valid for athletes. Further studies, both in the short term and throughout the seasons, are recommended about the natural variation of haematocrit in athletes.

Adult↗

PubMed1996

Intraindividual variations in lipoprotein (a) levels and factors related to these changes.

Lp(a) levels are genetically determined and remain stable without major changes throughout lives. However, when an individual's Lp(a) levels are observed over a one-year period, they show spontaneous variation. The rate of intraindividual variation in Lp(a) was observed in 16 patients with hypertension, hyperlipidemia and/or glucose intolerance in a chronic stable state who regularly visited the hospital clinic once a month, at least 10 times during the year, and in whom a total of 42 blood and clinical chemistry tests including serum lipids, Lp(a) and apoproteins were performed. The rate of annual intraindividual variation of Lp(a) averaged out as 16.6%. The rate was 18.8% for isoform S4 (n = 10), 18.6% for S3 (n = 3), and although small in number of subjects, other isoforms showed minor variation rates. There was a significant negative correlation between the rate of variation (y%) and LP(a) level (xmg/dl) r = -0.605, p < 0.05, y = -0.461 x +29.8). Therefore, when Lp(a) was high, the rate of variation (SD%) was low. This was consistent with the finding that the rates of variation were low for isoforms S2, S3S4 and F, whose molecular weights were low, accompanied by high Lp(a) levels. On the other hand, when the relationship between Lp(a) level and the amount of variation (SD mg/dl) was examined, there was no correlation between the two, since the amounts of variation were almost constant at a level of 3.8 mg/dl, regardless of Lp(a) level. The annual variation of Lp(a) level was found to be related to three groups of factors based on comparison of the variations among WHO phenotypes of hyperlipidemias, univariate correlation analysis with the clinical parameters tested, and multivariate analysis: the first group of factors was related to structure and metabolism of very low-density lipoprotein such as triglycerides, phospholipids, apo C-II, C-III, E, A-II and uric acid; the second group was related to thrombosis centering on platelets; and the third group involved those in the acute phase reactions represented by 1 hr and 2 hr erythrocyte sedimentation rates.

Adult↗

PubMed1992

Blood lipid measurements. Variations and practical utility.

OBJECTIVE: To describe the magnitude and impact of the major biological and analytical sources of variation in serum lipid and lipoprotein levels on risk of coronary heart disease; to present a way to qualitatively estimate the total intraindividual variation; and to demonstrate how to determine the number of specimens required to estimate, with 95% confidence, the "true" underlying total cholesterol value in the serum of a patient. DATA SOURCES: Representative references on each source of variation were selected from more than 300 reviewed publications, most published within the past 5 years, to document current findings and concepts. Most articles reviewed were in English. STUDY SELECTIONS: Studies on biological sources of variation were selected using the following criteria: representative of published findings, clear statement of either significant or insignificant results, and acquisition of clinical and laboratory data under standardized conditions. Representative results for special populations such as women and children are reported when results differ from those of adult men. DATA EXTRACTION: References were selected based on acceptable experimental design and use of standardized laboratory lipid measurements. DATA SYNTHESIS: The lipid levels considered representative for a selected source of variation arose from quantitative measurements by a suitably standardized laboratory. Statistical analysis of data was examined to assure reliability. The proposed method of estimating the biological coefficient of variation must be considered to give qualitative results, because only two or three serial specimens are collected in most cases for the estimation. CONCLUSIONS: Concern has arisen about the magnitude, impact, and interpretation of preanalytical as well as analytical sources of variation on reported results of lipid measurements of an individual. Preanalytical sources of variation from behavioral, clinical, and sampling sources constitute about 60% of the total variation in a reported lipid measurement of an individual. A technique is presented to allow physicians to qualitatively estimate the intraindividual biological variation of a patient from the results of two or more specimens reported from a standardized laboratory and to determine whether additional specimens are needed to meet the National Cholesterol Education Program recommendation that the intraindividual serum total cholesterol coefficient of variation not exceed 5.0. A National Reference Method Network has been established to help solve analytical problems.

Analysis of Variance↗

PubMed2005

Case-mix and variation in specialist referrals in general practice.

BACKGROUND: The potential of a comprehensive measure of patient morbidity to explain variation in referrals to secondary care has not previously been examined in the UK. AIM: To examine the relative role of age, sex and morbidity as defined by the Johns Hopkins ACG Case-Mix System in explaining variations in specialist referrals in general practice. DESIGN OF STUDY: Retrospective study of a cohort of patients followed for 1 year. SETTING: Two hundred and two general practices, with a total list size of 1,161,892, contributing data to the General Practice Research Database. METHOD: Each patient was assigned an ACG and morbidity group, based on their diagnoses, age and sex. The variability in referrals explained by these factors was examined using multilevel logistic regression models by splitting it into variation between practices and variation between patients within practices. RESULTS: The annual median (range) percentage of patients referred was 14.8% (range = 2.4-24.4%). The percentage of patients referred increased with age and morbidity. Morbidity explained 30.4% of the total variation in referrals (composed of variability between and within practices). Age and sex only explained 5.3% of the total variation. The variation attributable to practices was approximately 5%, thus most of the variation occurred within practices. Morbidity was also identified as a better predictor of referral compared to age and sex. CONCLUSIONS: Morbidity explains almost six times more of the variation in general practice referrals than age and sex, although about two-thirds of the variation remains unexplained. Most of the unexplained variation is due to differences within rather than between practices. The amount of variability in referrals between practices may be less than implied by previous studies based on aggregate information. The implications are that any investigation of specialist referrals from general practice should be interpreted cautiously, even after adjustment for age, sex and morbidity.

Adolescent↗

PubMed2005

[Relationship of the intensity of Schistosoma japonicum infection to the variation in individual egg count].

OBJECTIVE: To investigate the relationship of the intensity of Schistosoma japonicum infection with the variation in individual egg counts. METHODS: Stool specimens were collected from residents in a village in Jiangxi Province and examined with Kato-Katz thick smear method for seven consecutive days. Two smears were prepared and microscopically examined for each specimen. 570 individuals completed the investigation. Coefficient of variation (CV) was used to assess the intra-individual variation of the egg counts, in relation to the demographic characteristics including age, sex, occupation, and the intensity of infection. RESULTS: The proportion of individuals with at least one positive finding increased from 33.0% in a single measurement to 56.5% by seven measurements (P<0.01). The average intensity of infection in a single Kato-Katz test (111.06 EPG) was markedly higher than the average accumulated intensity of infection (42.51 EPG). Variation of intra-individual: the variation of CV in female infected subjects was higher than males (P<0.05). The variation of CV in 0-9 age group was higher than other age groups (P<0.05). The lowest variation of CV was detected in fishermen (P<0.05), but no statistical difference was found among other occupation groups. With an increase of the intensity of infection, the variation of CV decreased gradually. A negative correlation was observed between the variation of CV and the intensity of infection(r=-0.717, P<0.01). There was no significant difference in variation of CV between males and females, age and occupation groups when data were stratified according to the intensity of infection (P>0.05). CONCLUSION: The prevalence and intensity of S. japonicum infection by single Kato-Katz test was obviously lower than the real figures. The intensity of infection may be an essential factor that affects the intra-individual variation of egg counts.

Adolescent↗

PubMed1994

[Small area variations: surgery for hip fractures in the canton of Vaud].

OBJECTIVES: Studies of small area variations of health care utilization are more and more frequent. Such variations are often considered to be an indication of variations in the quality of medical care. The variations in the rate of operations for hip fractures are among the lowest studied to date, due to the fact that a consensus exists concerning this surgery. Our objective is to examine these variations within the context of relatively small and heterogeneous districts. METHOD: Based on anonymous computerized data on public hospital stays, this study describes the variations in population rates (crude and standardized) of operations for hip fracture among the health districts of the Canton of Vaud for the period from 1986 to 1991. District populations vary from 22,000 to 164,000. Using the extremal quotient (EQ), the importance of these variations was determined. RESULTS: The study population consists of 2363 cases, of which 78% are women. Mean age is 80.4 for women and 70.6 for men. Standardized rates of operation for hip fracture per 100,000 in the Canton Vaud for the years 1986 to 1991 are, respectively: 56; 67; 86; 91; 89 and 94. The EQ for the years 1986 to 1991 are respectively: 8.2; 4.0; 3.5; 2.7; 1.9 and 1.9. The high EQ, especially for the earlier years, are contrary to the initial premise of absence of variation. The progressive implementation in the Canton Vaud of VESKA medical statistics could play a role, as could the small size of many of the districts, with resultant instability of rates. CONCLUSIONS: Considering the wide variations shown here for an operation hardly regarded as subject to variations, it is important to exercise caution in interpreting published data of small area variations.

Aged↗