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PubMed2006

The use of parental data to evaluate soft tissues in an Anatolian Turkish population according to Holdaway soft tissue norms.

INTRODUCTION: The relative influence of genetic and environmental factors in the etiology of malocclusion has long been a matter for discussion. The aim of this study was to compare the soft tissue structures of parents and their prepubertal, pubertal, and postpubertal offspring according to the Holdaway soft tissue norms to determine the similarity among them. Differences related to age and sex between the parents and offspring were also evaluated. METHODS: Lateral cephalometric radiographs were used to determine the similarities in soft tissue structures in 120 families, which were divided into prepubertal (n = 40), pubertal (n = 40), and postpubertal (n = 40) groups according to the children's skeletal ages. A total of 12 variables (2 angular and 10 linear) were measured according to Holdaway's soft tissue analysis. Pairs were formed between family members (mother to son, mother to daughter, father to son, father to daughter, midparent (mean of the father's and mother's values) to son, and midparent to daughter) in each group. Descriptive statistics and multiple linear regression analysis were performed. RESULTS: Statistically significant correlations between parents and their offspring were found. The parental data showed that a mother's genetic influence on her child's soft tissues was greater than the father's. Moreover, it was found that daughters had greater genetic influences from their parents than did sons. As age increased, the similarity was greater. Soft tissue facial angle (beta: 0.671), soft tissue chin thickness (beta: 0.549), and basic upper lip thickness (beta: 0.537) were the most similar variables between parents and their offspring. CONCLUSIONS: A few selected cephalometric measurements of the parents might furnish important data to the clinician in predicting a child's facial growth characteristics and aging process.

Adolescent↗
PubMed1996

Single-subject methodology: an alternative approach.

The purpose of this paper is to identify and discuss an alternative experimental methodology, single-subject (SS) design. The primary premise for SS analyses forms the basis for many research questions in areas such as movement/motor control, individual performance patterns/strategies, and injury mechanisms. A brief historical perspective elucidating the evolution of modern-day group statistical techniques and the relationship to the individual is presented. Rationale for the SS design within this context is also discussed. Specific statistical applications include mean comparison tests (ANOVA, Model Statistics), correlation, and multiple regression. Validation of the underlying statistical assumptions of independence and normality relative to the applications are briefly discussed. Finally, several examples are included.

Data Interpretation, Statistical↗
PubMed2006

Long-term results in ossiculoplasty: an analysis of prognostic factors.

OBJECTIVES: The aim of the present study is to examine the prognostic factors based on 6-month and 5-year results of ossiculoplasty. STUDY DESIGN: Retrospective analysis was made on the ossiculoplasty cases in a county hospital. The information was extracted from a computer database. METHODS: All patients who had ossiculoplasty were routinely followed up in a dedicated ear audit clinic on a yearly basis. Between 1988 and 1999, 242 ossiculoplasties for chronic otitis media were performed on 197 patients. Only the first ossiculoplasty operation performed on each patient during the study period was included in the analysis. The 6-month and 5-year results were analyzed. Two different statistical methods were used--logistic regression analysis and the analysis of variance (ANOVA). A successful ossiculoplasty is defined as a postoperative air-bone gap (ABG) of 20 dB or better. RESULTS: The overall success rate of ossiculoplasty was 66.5% at 6 months and 50.3% at 5 years. In a multivariate analysis using logistic regression, those with present malleus were 6.36 times more likely to be successful. Using ANOVA, absent malleus and otorrhea were unfavorable factors of the 6-month ABG. Using logistic regression for the 5-year analysis, malleus remained a significant predictor at 5 years. Those with malleus were 2.65 times more likely to be successful. Using ANOVA, absent malleus was the only significant unfavorable factor of postoperative ABG at 5 years. In the univariate analysis, absent stapes and revision surgery are regarded as possible unfavorable factors. CONCLUSION: In the present study, the authors try to define the studied population (chronic otitis media) and the follow-up period (6 months and 5 years), and use logistic regression and ANOVA for statistical analysis. Absent malleus and otorrhea are important unfavorable factors for short-term outcome in ossiculoplasty (6 months), whereas absent malleus is the only important unfavorable factor for long-term outcome in ossiculoplasty (5 years).

Adolescent↗
PubMed2006

Safety practice and professional exposure to blood and blood-containing materials in serbian health care workers.

Safety practice is an important element of workplace safety and quality of health care. To investigate the safety practice and professional exposure to blood and blood-containing materials during a one-year period among Health Care Workers (HCWs) in Serbia. Cross-sectional study of 1559 Serbian HCWs using a self-administered questionnaire. Mantel-Haenszel statistics and multiple logistic regression analysis were used in statistical analysis. Fifty-nine percent (921) of HCWs had skin contact with patients blood, followed by 51% (791) with needle stick injuries, 38% (599) with cuts from sharp instruments, and 34% with contact of eye and other mucosa with patient's blood. Nurses reported professional exposure more often than others. Safety practices consisted of using appropriate barriers (gloves, mask, glasses) in all procedures with patients and were used by 58%, 23%, and 4% of HCWs, respectively. Doctors protected themselves more regularly than others. Hospital protocols for post exposure prophylaxis and safety disposal of medical waste are not common in Serbian health care settings. Safety practices in use were having hospital guidelines for safety practice in hospitals [odds ratio (OR)=1.58, 95% confidence interval (CI)=1.14-2.19], carrying out some form of intervention with risks of infection (OR=3.76, 95% CI=2.57-5.51), and HCWs aware of the professional risk of acquiring infection (OR=1.48, 95% CI=1.28-1.79). This study indicates that emphasis on work practice, attire, disposal systems and education strategies, should be employed to reduce professional exposure to blood and blood containing materials among HCWs in Serbia.

Adult↗
PubMed1999

Risk factors for pain and nausea following retinal and vitreous surgery under conscious sedation.

BACKGROUND: There have been no studies examining risk factors for pain and nausea during the first day after posterior segment surgery. We performed a study to identify significant risk factors for the development of pain and nausea during the first 24 hours after outpatient vitrectomy or scleral buckle surgery. METHODS: A total of 257 consecutive patients who underwent vitrectomy (192 patients), scleral buckling (57 patients) or combined vitrectomy-scleral buckling (8 patients) between July 1 and Dec. 31, 1995, were enrolled in this prospective study. The patients' age, sex and ethnicity, the duration of the procedure and the intraoperative use of minor tranquillizers, hypnotic agents, narcotic analgesics or major tranquillizers were recorded. Each patient rated his or her postoperative pain and nausea on two separate 100-mm lines. The left end of the line represented no pain (or nausea) whatsoever, and the right end of the line represented severe pain (or nausea). The distance of the recorded point from the origin of the line was used as the outcome measure for pain and nausea. All the data were analysed statistically by means of logistic regression analysis and descriptive statistics. RESULTS: The median pain scores were 1.0 for the patients who underwent vitrectomy, 47.0 for those who underwent scleral buckling and 35.0 for those who underwent combined vitrectomy-scleral buckling. The median nausea scores were 14.5, 45.0 and 55.5 respectively. The only variable that was identified as a predictor of postoperative pain or nausea was the intraoperative use of narcotic analgesics: in the vitrectomy group, postoperative nausea occurred almost three times as often among patients who received these agents as among those who did not (odds ratio 2.6, p = 0.00). INTERPRETATION: The identification of the intraoperative use of narcotic analgesics as a risk factor for nausea in the first 24 hours after outpatient vitrectomy suggests that, when possible, these agents should be avoided during surgery.

Adolescent↗
PubMed1978

[A method for describing monotonic dose-effect curves and areas in yes/no reactions (author's transl)].

A method combining a polynomial statistical model and multiple probit regression, is useful in describing nonmonotonic dose-effects in yes/no-reaction variables. An example shows the application of this method to the combination of two substances. The effects can be described with a minimum of polynomial coefficients. The application of a simple X2-test allows to test for additivity of substance effects by testing whether interaction coefficients improve the fit of the model significantly or not.

Computers↗
PubMed1987

Linear regression analysis of ultrasound follicular growth series: statistical relationship of growth rate and calculated date of growth onset to total growth period.

Linear regression analysis was used to assess the serial growth of carefully measured individual mean follicular diameters as a function of menstrual age in a group of normal volunteers in natural, unstimulated cycles (n = 18). Follicle diameter (FD) growth, as measured with serial pelvic ultrasonography, can be shown to be essentially linear (mean R2, 0.92) with respect to time up to the point of ovulation. Growth rate (k) and the calculated date of growth onset (Do) are obtainable from the individual regression equations. Because an approximation of the date of ovulation (Dov, measured by menstrual age at the date of peak mean follicular size) is an available parameter, total growth period (TGP) is calculated with the equation (TGP = Dov - Do). Do, k, and TGP are highly correlated with one another. The mean parameters (+/- standard deviation) are Do = 4.29 +/- 2.77 day, k = 0.24 +/- 0.07 cm/day, TGP = 10.32 +/- 2.35 day, peak FD = 2.34 +/- 0.28 cm, and Dov = 14.61 +/- 2.00 day. The internal correlation of these parameters predicts that information from the first several scans in an individual series may be used to forecast date of ovulation. This may represent an improvement over the use of follicle size or menstrual age alone in planning for human chorionic gonadotropin administration, insemination timing, follicular aspiration and other interventions.

Adult↗
PubMed1998

Validity of linear regression in method comparison studies: is it limited by the statistical model or the quality of the analytical input data?

We compared the application of ordinary linear regression, Deming regression, standardized principal component analysis, and Passing-Bablok regression to real-life method comparison studies to investigate whether the statistical model of regression or the analytical input data have more influence on the validity of the regression estimates. We took measurements of serum potassium as an example for comparisons that cover a narrow data range and measurements of serum estradiol-17beta as an example for comparisons that cover a wide data range. We demonstrate that, in practice, it is not the statistical model but the quality of the analytical input data that is crucial for interpretation of method comparison studies. We show the usefulness of ordinary linear regression, in particular, because it gives a better estimate of the standard deviation of the residuals than the other procedures. The latter is important for distinguishing whether the observed spread across the regression line is caused by the analytical imprecision alone or whether sample-related effects also contribute. We further demonstrate the usefulness of linear correlation analysis as a first screening test for the validity of linear regression data. When ordinary linear regression (in combination with correlation analysis) gives poor estimates, we recommend investigating the analytical reason for the poor performance instead of assuming that other linear regression procedures add substantial value to the interpretation of the study. This investigation should address whether (a) the x and y data are linearly related; (b) the total analytical imprecision (s(a,tot)) is responsible for the poor correlation; (c) sample-related effects are present (standard deviation of the residuals >> s(a,tot)); (d) the samples are adequately distributed over the investigated range; and (e) the number of samples used for the comparison is adequate.

Chromatography, Ion Exchange↗
PubMed2005

The problem of analysing the relationship between change and initial value in oral health research.

The relationship between initial disease status and subsequent change following treatment has attracted great interest in dental research. However, medical statisticians have repeatedly warned against correlating/regressing change with baseline because of two methodological concerns known as mathematical coupling and regression to the mean. In general, mathematical coupling occurs when one variable directly or indirectly contains the whole or part of another, and the two variables are then analyzed by using correlation or regression. Consequently, the statistical procedure of testing the null hypothesis - that the coefficient of correlation or the slope of regression is zero - may become inappropriate. Regression to the mean occurs with any variable that fluctuates within an individual or a population, either owing to measurement error and/or to physiological variation. The aim of this article was to clarify the conceptual confusion around mathematical coupling and regression to the mean within the statistical literature, and to correct a popular misconception about the correct analysis of the relationship between change and initial value. As examples that use inappropriate methods to analyze the relationship between change and baseline are still found in leading dental journals, this article seeks to help oral health researchers understand these problems and explain how to overcome them.

Algorithms↗
PubMed2005

Correlation between capillary blood flow of retina estimated by SLDF and circulatory parameters of retrobulbar blood vessels estimated by CDI in diabetic patients.

BACKGROUND: The aim of this study was to investigate the correlation between the recordings of scanning laser Doppler flowmetry (SLDF) of the retina and the recordings of color Doppler imaging (CDI) of the retrobulbar circulatory parameters in diabetic patients without diabetic retinopathy. METHODS: Twenty-three diabetic patients without diabetic retinopathy were evaluated using SLDF for the apparent retinal circulation and using CDI for the apparent retrobulbar circulation in the central retinal artery, the central retinal vein and the short posterior ciliary artery. The circulatory parameters estimated in the retinal tissue using SLDF were velocity, volume and flow. The Circulatory parameters that were recorded using the CDI method were peak systolic velocity (PSV), end-diastolic velocity (EDV), mean velocity (MV), pulsatility (PI) and resistivity index (RI). We obtained the correlation coefficients between parameters of SLDF and CDI. Multiple regression analysis was performed with "flow" parameter of SLDF recordings as a dependent variable and all estimated CDI parameters as independent variables. Multiple linear regression was also performed, including the "flow" parameter of SLDF recordings as a dependent variable and PI of the CDI parameters of all the measured blood vessels as independent variables. RESULTS: The "velocity" parameter of SLDF was significantly correlated with the PI in the central retinal artery (P=0.02), PI and RI in the central retinal vein (P=0.01; P=0.01) and the PSV, MV, PI and RI in the short posterior ciliary artery, as recorded by CDI (P=0.003; P=0.02; P=0.002; P=0.01). The "volume" parameter of SLDF was significantly correlated with the PI and RI in the central retinal vein (P=0.03; P=0.03) and the PSV in the short posterior ciliary artery (P=0.03), as recorded by CDI. The "flow" parameter of SLDF was significantly correlated with the PI and RI in the central retinal vein (P=0.01; P=0.01) and the PSV, MV, PI and RI in the short posterior ciliary artery (P=0.003; P=0.03; P=0.002; P=0.01) as measured by CDI. The multiple regression analysis was statistically non-significant (P=0.86). The multiple linear regression analysis indicated that from among the PI of the evaluated blood vessels, the PI of the short posterior ciliary artery was the most significant predictor of the "flow" parameter of SLDF (P=0.01). CONCLUSION: This study suggests a positive correlation between the recordings of SLDF of the retinal tissue and the retrobulbar circulatory parameters of the CDI in diabetic patients without diabetic retinopathy.

Blood Flow Velocity↗
PubMed2004

Value of preoperative urethral ultrasound in optic internal urethrotomy.

INTRODUCTION AND OBJECTIVES: The recurrence rate of internal urethrotomy (IU) is still high (long-term curative success rate between 20 and 45% after the first IU). We aimed to establish in a prospective randomized trial the value of urethral ultrasound in inflammatory urethral stricture (IUS) diagnosis and treatment. PATIENTS AND METHODS: Between June 1994 and January 2004, we performed IU in 562 cases with IUS (under 1.5 cm). In order to evaluate the results obtained by guided incision according to the echographic evaluation, patients have been divided into 2 groups. For the first group (319 cases), the IU technique has been adapted to the echographic aspect of the stricture zone, and to the fibrosis location on the urethral circumference. For patients of the second group (243 cases) we practiced IU with a "classical" 12 o'clock incision. The mean follow-up period was 38.7 months (range 4-71 months) and 37.9 months (range 5-69 months) for the second group. We used the SPSS 8.0 for Windows statistical analysis (Cox regression) with Kaplan-Meier curves in order to compare the recurrence-free survival time. RESULTS: In the first group (44.5% recurrence rate) we found 4 specific locations of urethral stricture fibrosis according to ultrasound evaluation: dorsal urethral fibrosis (274), ventral urethral fibrosis (36), circular urethral fibrosis (136), dorsal and ventral fibrosis (114). The best results have been obtained for the dorsal and ventral location of the spongious fibrosis (45/153 recurrences, 29.4% and 9/22 recurrences, 41%). The recurrence rate was higher in the circular and concomitant dorsal and ventral location of the spongious fibrosis: 67.5% (52/77 cases) and 55.2% (37/67 cases). Cox regression (-2LL=360.859, chi2=47.670, Sig=0.137) demonstrated statistical significance in these series (p<0.5). In the second group (51.5% recurrence rate) we found 64.2% recurrences for the ventral location, 83% for the circular location and 72.3% for the dorsal and ventral location of the spongious fibrosis. CONCLUSIONS: According to our experience, the high recurrence rate of IUS after IU may be explained by the inadequate type of incision. So, urethral ultrasound could improve the IU technique by better location of the fibrosis area.

Disease-Free Survival↗
PubMed2005

Using ergodic theory to assess the performance of ecosystem models.

Ecosystem simulation models are designed to assess the flux of energy, water, carbon and nitrogen according to a given vegetation type. The reliability of the modeled results is determined by model validations. Model validations are typically done using classical statistical methods like regression analysis of predicted versus observed values, paired t statistics and error assessment procedures to characterize the quality of current and future model predictions. All these validation efforts concentrate on static aspects of the model but fail to describe the model dynamics. In this paper, we introduce methods from ergodic theory to analyze the dynamic behavior of ecosystem models. We describe (1) how the attractor representation of model behavior can be reconstructed from a time series of model outputs, and (2) what we can learn from the attractor to assess the model dynamics. As an application example, we provide simulation results for two important pine forest ecosystems in Austria, i.e., 23 Cembran pine and 16 Scots pine stands. These stands were simulated with three model parameterizations: one representing a generic, evergreen needle-leaf forest, and two species- specific parameter sets, one for Cembran pine and one for Scots pine. First, we applied standard validation methods to get static measures of model accuracy and precision. Next, we used ergodic theory to assess model dynamics. A comparison of both analyses reveals important issues related to model dynamics, such as the finding that the occurrence of instabilities in model behavior may not be detected by standard validation methods. Using ergodic theory, we were able to reconstruct the attractors of model behavior. In the attractor describing model dynamics for Cembran pine, simulated with the generic, evergreen needle-leaf forest parameter set, we detected instability in model behavior. We identified this instability as a riddled basin configuration, which is a strong indicator for the occurrence of a chaotic model behavior that may result in random predictions. Our results suggest that ergodic theory is a useful tool for assessing inconsistencies in the dynamics of ecosystem model simulations that have not been detected by standard statistical validation methods.

Climate↗
PubMed2006

Detection of carryover in automated milk sampling equipment.

Equipment for sampling milk in automated milking systems may cause carryover problems if residues from one sample remain and are mixed with the subsequent sample. The degree of carryover can be estimated statistically by linear regression models. This study applied various regression analyses to several real and simulated data sets. The statistical power for detecting carryover milk improved considerably when information about cow identity was included and a mixed model was applied. Carryover may affect variation between animals, including genetic variation, and thereby have an impact on management decisions and diagnostic tools based on the milk content of somatic cells. An extended procedure is needed for approval of sampling equipment for automated milking with acceptable latitudes of carryover, and this could include the regression approach taken in this study.

Animals↗
PubMed1991

Using the correct regression analysis technique in method comparison studies.

Regression analysis frequently is used to evaluate a new clinical laboratory method. Results from the new method are compared to results from an existing more established method. If measurement error exists in the established method, then least squares may not be an appropriate statistical method to use for the regression analysis. An errors variable regression analysis model was used to evaluate data from five method comparison studies. Results were compared to least squares analyses performed on the same data. When significant measurement error existed in the "reference" method, the errors variable analysis provided a less biased estimate of the regression statistics, which differed markedly from the least squares results. Inappropriate use of least squares in method comparison studies can lead to erroneous conclusions about the relationship of a new analytical method to an existing method.

Journal Article↗
PubMed2006

[A study on the effect of Oncomelania hupensis hupensiss killed with niclosamide in China].

OBJECTIVE: To study the effect of Oncomelania hupensis hupensis of niclosamide, and exploring the main influencing factors. METHODS: The samples of Oncomelania hupensis hupensis were collected from 37 sampling sites in 33 counties of 10 provinces by means of stratified random sampling methods in accordance with the categories of Oncomelania hupensis hupensis habitats. Samples were randomly located into study group and control group. Oncomelania hupensis hupensis of the study group was marinated in different concentration liquor of niclosamide which was confected with water for 24 hours or 48 hours, then LC50 of niclosamide by which Oncomelania hupensis hupensis was killed and amount calculated. The influencing factors of the mortality of Oncomelania hupensis hupensis in the study group was statistically analyzed by 2 test and by multiple logistic regression using SPSS 13.0 statistical software. RESULTS: The mortality of Oncomelania hupensis hupensis of the two test groups which were marinated in 0.5 mg/L liquor for 48 hours and 1.0 mg/L liquor for 24 hours was 100%. The effect of Oncomelania hupensis hupensis killed by niclosamide was markedly reduced along with the reduction of drug concentration. The average LC50 rates of niclosamide liquor by which Oncomelania hupensis hupensis killed for the 24 hours and 48 hours in the study group, were 0.0939 mg/L and 0.0625 mg/L, respectively. There was significant difference between the two test groups (chi(2) = 5.001, P <0.01) . In determinate range of concentration, the mortality of Oncomelania hupensis hupensis showed significant difference among the geographic types of habitat ( chi(2) = 4.264, P < 0.05). By means of multiple logistic regression using SPSS 13.0 statistical software, the estimate value of coefficient of regression on the influence factors, drug concentration, test time and the geographic types of habitat were 2. 047 ( OR = 5. 573), 0.263 ( OR = 2.924) and 0. 187- 0.210 ( OR = 1.969- 2. 560), respectively. CONCLUSION: Niclosamide could kill Oncomelania hupensis hupensis effectively. The main influencing factors on the efficacy of niclosamide by which Oncomelania hupensis hupensis was killed, appeared to be drug concentration, time of testing and the geographic types of habitat.

Animals↗
PubMed1991

Use of brain biopsy for diagnostic evaluation of patients with suspected herpes simplex encephalitis: a statistical model and its clinical implications. NIAID Collaborative Antiviral Study Group.

Using the decision analysis technique and multivariate regression methods, a statistical model was established to define the utility of brain biopsy for diagnostic evaluation of patients with suspected herpes simplex encephalitis (HSE). Two strategies were compared: strategy I, brain biopsy with acyclovir (ACV) treatment for 10 days in biopsy-positive patients, and strategy II, ACV therapy without brain biopsy. Strategy I resulted in a greater 6-month survival rate when the likelihood of patients having HSE was less than 70%. Based on the current estimated prevalence of HSE (for patients with suspected HSE) of 35%, strategy I showed a slight advantage of a 3.2% increase in 6-month survival rate. An individual patient's chance of a positive brain biopsy can be predicted using a mathematical equation based on several important clinical assessments. This equation in conjunction with the decision analysis is a useful guide for the clinical management of patients with regard to brain biopsy.

Acyclovir↗
PubMed1990

Testing the Hardy-Weinberg equilibrium in the HLA system.

A new method of testing the Hardy-Weinberg equilibrium in the human leukocyte antigen (HLA) system is proposed and applied to real data. The derivation is based on the maximum likelihood method and closely related to standard regression theory. The test statistic has a closed representation of residual sum of squares by a projection mapping of data onto the estimated regression plane. Under the Hardy-Weinberg law the noniterative estimates for the gene frequencies are suggested by the use of the projection mapping. The test statistic and gene frequency estimates are shown to be asymptotically equivalent to the maximum likelihood method and to be more efficient than the other suggested test statistic when there are more than two identified alleles.

Biometry↗
PubMed1996

Preneoplastic lesions and gallbladder cancer: an estimate of the period required for progression.

BACKGROUND & AIMS: Scarce biological information exists about the importance of preneoplastic lesions in gallbladder cancer. The aim of this study was to estimate the time required for the sequence of dysplasia (DY) to carcinoma of the gallbladder. METHODS: Eighty-four cases of DY, 60 cases of early carcinomas (ECs), 181 cases of advanced carcinomas (ACs), and 121 cases of metastatic (ME) gallbladder cancer were analyzed. Age was used as the main parameter. Statistical analysis was performed using analysis of variance and multiple regression analysis. RESULTS: Among all cases, the mean age of female patients was lower than the mean age of male patients (P = 0.001). A significant difference in mean age between sexes by specific type of lesion was also observed (P < 0.001). The mean age was 46.3 years (SD, 16) in the DY group, 57.5 years (SD, 16.7) in the EC group, 59 (SD, 13.7) in the AC group, and 61.1 (SD, 12.1) in the ME group. Multiple regression analysis showed statistically significant differences (r = 0.386; P < 0.001) in the mean age of patients with dysplastic lesions compared with the carcinoma group. CONCLUSIONS: According to these observations, the period required to progress from dysplasia to advanced gallbladder carcinoma would be around 15 years, observing a continuum in the progression of the lesions.

Adult↗