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Results for “time series”

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At least 19 recordsLinked to original sources

PubMed1992

A time series investigation of three nicotine regulation models.

Time series data were collected twice daily for 62 days from 10 individuals on three variables related to smoking habit strength: number of cigarettes smoked, salivary cotinine, and carbon monoxide. The two purposes of this study were: (a) to evaluate which time series model(s) best fits each of the measures; and (b) to determine which model of nicotine regulation is consistent with the data. Three models of nicotine regulation were considered: (a) nicotine fixed effect; (b) nicotine regulation; and (c) multiple regulation. These models provide different predictions about the size and direction of the lag-one autocorrelation. Each measure was described in terms of one of a family of time series models represented mathematically as ARIMA (p, d, q). Models varied by individual, but a single model described the majority of subjects for all three variables. The clearest model identification was for the number of cigarettes smoked where an ARIMA (1, 0, 0) model with a moderate to strong negative dependency fit the majority of the subjects. This provided strong support for the multiple regulation model. An appendix provides a brief review of time series methodology.

Adult↗

PubMed1977

[Determining the effectiveness of therapeutic interventions in a time series of examination plans].

Some typical effects of therapeutic intervention in time series designs are considered and suggested for heuristic evaluation by Kendall-tests. The pre-intervention phase is assumed to be stationary as to an indicator variable and the post intervention phase is assumed to change in level or direction. According to the effects assumed, anchor series of ranks are constructed and compared to rank-transformed time series observations. Large Kendall-scores indicate agreement between assumed and observed series of ranks, i. e. either change in level and/or in direction.

Humans↗

PubMed1992

Chronolab: an interactive software package for chronobiologic time series analysis written for the Macintosh computer.

Methods based on periodic regression have been designed for the detection of periodic components in short, noisy, and nonequidistant time series (as they are usually present in medicine and biology). The procedure consists of fitting a set of (cosine) curves to the data, with the analyst choosing the domain of trial periods to be analyzed and the distance between consecutive trial periods. We here describe an interactive program for least-squares rhythmometry written in C language for the Macintosh computer. For any given number of time series to be analyzed at once, the program is able to perform two different kinds of analyses: (a) linear in time, for the sequential fit of trial periods; and (b) linear in frequency, for the sequential fit of harmonic components from an initial fundamental period. For each series and for each trial period fitted to the data, the program gives the following information: fitted period; percent rhythm; p value from testing the assumption of zero amplitude; rhythm-adjusted mean or mesor, amplitude, and acrophase, each with corresponding standard errors and 95% confidence intervals when the component is statistically significant; and (when required by the analyst) p values from tests of sinusoidality, normality of residuals, and homogeneity of variance. Additionally, the program provides a summary report for each time series analyzed, including descriptive statistics such as the number of data analyzed for that series, minimum, maximum, arithmetic mean, standard deviation, standard error, 90% range, and 50% range. The analyst is also able to transform the data before doing any rhythmometric analysis. Transformations already integrated in the program include square root, logarithm, inverse, data as percentage of mean, data as percentage of mesor, and elimination of values outside +/- 3 SD from the mean. When several periods are suspected to be statistically significant, a multiple-component analysis can be also used by the concomitant least-squares fit of several harmonics. The program allows the simultaneous analysis of several periods in several variables from several individuals, with limitations depending solely on internal memory availability and speed requirements from the user. When series from different subjects or different variables in the same subject are available for analysis, a parameter test also included in the program can be used for comparison of rhythm characteristics at any given period. All information required in a single analysis is given by the analyst in the form of self-explanatory commands grouped in different "menus."(ABSTRACT TRUNCATED AT 400 WORDS)

Biometry↗

PubMed1978

Cluster analysis of respiratory time series.

We have investigated the respiratory control system with the hypothesis that, although many variables such as minute ventilation (VI), tidal volume (VT), breathing period (TT), inspiratory duration (TI), and expiratory duration (TE) may be observed, the controller functions more simply by manipulating only 2 or 3 of these. Thus, if tidal volume is the only independent variable, TI being determined by the "off-switch" threshold, these variables should have very similar time courses. Anesthetized dogs were subjected to CO2 breathing and carotid sinus perfusion to stimulate both chemoreceptors. The time series of the variables VI, VT, TT, TE, and TI as well as PACO2 were determined on a breath by breath basis. Derived characteristics of these time series were compared using Cluster Analysis and the latent dimensionality of respiratory control determined by Factor Analysis. The characteristics of the time series clustered into 4 groups: magnitude (of the response), speed, variability and relative change. One respiratory factor accounted for 86% of the variance for the variability characteristics, 2 factors for magnitude (91%) and relative change (85%) and 3 factors for speed (89%). The respiratory variables were analysed for each of the 4 groups of characteristics with the following results: VT and TI clustered together only for the magnitude and relative change characteristics where as TT and TE clustered closely for all four characteristics. One latent factor was associated with the [TT-TE] group and the other usually with PACO2.

Animals↗

PubMed1992

Time series cross-correlation analysis of postparturient relationships among serum metabolites and yield variables in Holstein cows.

Time series cross-correlation analysis was used to determine relationships among serum beta-hydroxybutyrate, glucose, FFA, cholesterol, milk yield, DMI, and estimated net energy balance for 42 d postpartum for 14 multiparous cows. Milk yield was positively associated with beta-hydroxybutyrate concentrations on the same day, and milk yield was a primary determinant of metabolic change. Dry matter intake was negatively correlated with beta-hydroxybutyrate concentrations 3 d later and on the same day. The data supported in vitro studies showing that FFA are positively associated with beta-hydroxybutyrate production, showed that glucose concentrations are negatively cross-correlated with beta-hydroxybutyrate concentrations, and found that estimated net energy balance is negatively cross-correlated with beta-hydroxybutyrate. Analyses suggested that serum glucose and cholesterol concentrations significantly decreased with increased milk yield; analyses also suggested that elevated beta-hydroxybutyrate concentrations were associated with decreases in milk yield 6 d later. beta-Hydroxybutyrate and FFA concentrations 3 to 9 d before parturition were positively related to cholesterol concentrations, and relationships were positive between estimated net energy balance and cholesterol, suggesting that cholesterol concentrations increased as precursors for cholesterol synthesis were available. Time series cross-correlation analysis was a useful tool in examining relationships among variables when repeated samples were obtained from the same individuals.

3-Hydroxybutyric Acid↗

PubMed1979

A time series approach to forecasting Australian total live-births.

The relationship between classical demographic deterministic forecasting models, stochastic structural econometric models and time series models is discussed. Final equation autoregressive moving average (ARMA) models for Australian total live-births are constructed. Particular attention is given to the problem of transforming the time series to stationarity (and Gaussianity) and the properties of the forecasts are analyzed. Final form transfer function models linking births to females in the reproductive age groups are also constructed and a comparison of actual forecast performance using the various models is made. Long-run future forecasts are generated and compared with available projections based on the deterministic cohort model after which some policy implications of the analysis are considered.

Australia↗

PubMed1992

Fibromyalgia: a time-series analysis of the stressor-physical symptom association.

The purpose of this study was to investigate the association among daily stressors, cognitive rumination, and fibromyalgia symptoms using time-series methodology and to determine whether autocorrelation was present in the self-report data. Twelve female fibromyalgia subjects monitored their daily level of stressors, cognitive rumination, and fibromyalgia symptoms for 30-35 days. Time-series regression analyses indicated that there was a positive association between previous-day stressors and fibromyalgia symptoms for one subject and between previous-day cognitive rumination and fibromyalgia symptoms for four subjects. For 7 out of 12 subjects autocorrelation was present, and generalized least-squares methods were used with these subjects. These results indicate that ordinary least-squares methods may often not be appropriate for within-subject designs with self-report data. These results also question the often reported stressor-physical symptom association. This study illustrates a useful methodology and analysis to investigate psychosocial-physical symptom associations.

Adult↗

PubMed1977

[A psychophysiologic time series study with 20 students over 8 weeks].

A longitudinal (time series) study was performed (N = 20 students; T = 16 points of observation during 8 weeks) on a considerable number of psychological and physiological variables to investigate the suitability of these parameters for general and individual state change description. Some problems of correlational analysis and the generality-individuality-dilemma of this kind of research are discussed.

Adult↗

PubMed1992

Time series analysis of glottal airflow in normal and pathological phonation.

Time series analysis of glottal airflow was carried out on 26 normal controls and 40 patients with voice disorders, using a modification of Isshiki's original technique which uses a hot-wire flowmeter, taking cycle-by-cycle fluctuations into consideration. The mean flow rate and mean AC/DC were shown to have significant differences among normal and patient groups. The standard deviations of AC/DC and AC/DC perturbation were calculated from the AC/DC value of 50 cycles and shown not to vary significantly among the normal and patient groups. The relationship between AC/DC and perceptual impression of voice was also studied among 20 selected patients with breathy voices. Using Spearman's rank correlation coefficient, this relationship was found to have statistical significance (P < .05).

Glottis↗

PubMed2025

Universal versus targeted chlorhexidine and mupirocin decolonisation and clinical and molecular epidemiology of Staphylococcus epidermidis bloodstream infections in patients in intensive care in Scotland, UK: a controlled time-series and longitudinal genotypic study.

BACKGROUND: There are concerns that biocide skin and mucous membrane decolonisation, which is widely used to prevent health-care-associated infections in intensive care units (ICUs), might select for multidrug-resistant pathogens. We aimed to evaluate the effects of de-escalating from universal to targeted skin and nasal decolonisation on Staphylococcus epidermidis bloodstream infections (SE-BSI). METHODS: We did a retrospective, before-after-control-impact time-series analysis and longitudinal genotypic study in two ICUs with divergent decolonisation practice in tertiary care hospitals of adjacent health boards in Scotland, UK. Participants were aged at least 16 years and admitted between July 1, 2009, and Feb 28, 2022. There were no exclusion criteria for the study. In ICU one (intervention site) universal decolonisation in all admissions was de-escalated to targeted decolonisation of meticillin-resistant Staphylococcus aureus (MRSA) carriers on Feb 1, 2019, while in ICU two (control site) targeted decolonisation was applied throughout. We collected bloodstream infection data from all causes, including clinically significant SE-BSI. Antimicrobial susceptibility testing was used to define meticillin-resistant S epidermidis (MRSE) and chlorhexidine susceptibility. We used multilocus sequence typing to identify sequence types from archived SE-BSI isolates. Whole-genome sequencing was applied to a sample from ICU one. The primary outcomes were incidence densities of all bloodstream infections, SE-BSI, and meticillin-resistant S epidermidis bloodstream infections (MRSE-BSI), and the percentage probability that SE-BSI were MRSE-BSI. The effects of de-escalation on primary outcomes were estimated by differences between the intervention and control sites, before and after de-escalation, using a before-after-control-impact time-series design. Secondary outcomes included the proportion of multidrug resistant sequence types, carriage of mobile genetic elements and genes for multidrug resistance and biofilm production. FINDINGS: Between July 1, 2009, and Feb 28, 2022, S epidermidis was identified in 334 (45%) of 735 bloodstream infections in ICU one, of which 197 occurred before the de-escalation intervention in Feb 1, 2019, and S epidermidis was identified in 167 (60%) of 278 bloodstream infections in ICU two. There was no increase in all bloodstream infection incidence coinciding with de-escalation in ICU one, whereas MRSE-BSI incidence declined significantly from 10·4 cases per 1000 occupied bed days (OBDs; 95% credible interval [CrI] 7·2-15·4) to 4·3 cases per 1000 OBDs (2·5-6·7), as did the percentage probability of MRSE (from 89·2%, 95% CrI 77·8-96·5 to 56·7%, 34·3-77·5%). No significant changes in the primary outcomes were seen in ICU two. MRSE-BSI incidence density was positively associated with chlorhexidine use, but not mupirocin use. De-escalation was associated with a reduced proportion of SE-BSI due to multidrug-resistant sequence types and reduced carriage of mobile genetic elements and genes for multidrug resistance and biofilm production, as observed by multi-locus sequence typing and whole genome sequencing. INTERPRETATION: In ICU settings with low MRSA incidence, the benefits of universal decolonisation should be balanced against the risks of selecting MRSE sequence types adapted for invasive and device-associated infection. FUNDING: National Health Service Grampian Charity.

Humans↗

PubMed1992

[Treatment of atopic dermatitis with borage seed oil (Glandol)--a time series analytic study].

The therapy of atopic dermatitis with highly unsaturated fatty acids has witnessed a renaissance in the last years. Therefore, a study was conducted with borage oil (Glandol), rich in highly unsaturated, so-called omega fatty acids, against palm seed oil as placebo in a total of 12 patients. Evaluation of the severity of the skin changes was done by means of the ADASI (Atopic Dermatitis Area and Severity Index)-score system described by us recently. The ADASI-scores, forming a time series, were analyzed by trend analysis methods. These methods allow an evaluation of the effectiveness of the therapy in each case. The analysis revealed that five out of seven patients treated with borage oil showed a favourable effect with regard to the skin changes assessed by the ADASI-score. In contrast, only one out of the five patients treated with placebo showed a significant improvement in skin changes. In view of the positive effect ob borage oil in patients with atopic dermatitis, a trial therapy for a certain period seems justified. Our study demonstrates both the value of our ADASI-scoring system as well as the advantages that time series or trend analysis methods might have for the evaluation of therapeutic effects in chronic skin diseases such as atopic dermatitis.

Administration, Oral↗

PubMed1975

[Neurophysiologic application of a system for the study of simple and multiple time series analyses].

By means of the most used methods at present of time series analysis, the authors describe a modular package allowing a non-specialised user to process by himself experimental results. Probability sets may be calculated, drawn and statistically tested from direct or transformed data. The use of this package is made easier by means of an automation table which chooses the necessary parameters and memorises responses so as to avoid superfluous problems. The FORTRAN IV coded program is run on a PDP 10 under time-sharing for the analysis of the data concerning action potentials in neurophysiology.

Computers↗

PubMed1978

The use of grafted polynomials and dummy variables in analyzing time series data.

Describes an innovative statistical method for analyzing single-S time series data. The S and data in the paper were selected from a larger study which applied operant conditioning to ambulation problems of severely handicapped patients and used positive verbal reinforcement. The method described is a variation of traditional multiple regression analysis described elsewhere as "grafted polynomials" (Draper & Smith, 1967; Fuller, Note 1). An extensive explanation of the use of dummy variables also is provided.

Conditioning, Operant↗

PubMed1992

Identification of pulses in hormone time series using outlier detection methods.

The identification of discrete hormonal secretory pulses is of critical importance in clinical endocrinology. Pulses are defined as sudden increases in hormone concentration followed by exponential decay. We propose a model-based iterative procedure for pulse detection in pulsatile hormone time series. Our model is seen to be analogous to the model for innovation outliers in autoregressive series, and outlier detection techniques for pulse identification are adapted to the endocrine context. An original feature of the procedure is that it distinguishes between true pulses and gross observation outliers in the series. Simulation experiments are used to investigate the behaviour of the method under physiologically or clinically relevant circumstances. Five experimental endocrine series from rhesus monkeys, where the times of the pulses are known from the concomitant recording of the electrical activity of the hypothalamus, are analysed.

Animals↗

PubMed1992

Annual and sub-annual rhythms in human conception rates: time-series analyses show annual and weekday but no monthly rhythms in daily counts for last normal menses.

Methods of time-series analysis, which are widely used to good effect in physical sciences and econometrics, have found little use in much-needed analyses of cyclical biological phenomena. Here we apply those methods to analyses of rhythmic patterns in human conception rates. Our results confirm the annual periodicity of monthly counts of total viable conceptions, demonstrate a weekday rhythm reflecting interaction of conjugal coital rhythms with individual menstrual fertility cycles, and find no evidence of any other significant repeating pattern.

Artifacts↗

PubMed1992

Application of time-series analysis for the recognition of increases in urinary estrogens as markers for the beginning of the potentially fertile period.

Time-series analysis was applied to the urinary total estrogen data from 142 ovulatory menstrual cycles to determine the first statistically significant increase as a marker for the beginning of the potentially fertile phase. Application of the Trigg's tracking signal to each cycle detected an increase in urinary total estrogens above the baseline in every case, with a cumulative probability of > or = 95%. The distribution of first increase days ranged from 10 days before 3.5 days before the presumed day of ovulation with a mean of 6.5 +/- 1.4 days. The significant parameters in the calculation of the tracking signal are the smoothing constant (alpha) which is related to the number of baseline observations, the baseline mean for the cycle, and the variation of the baseline mean. The method allows a calculation of the tracking signal as the cycle unfolds and a statistical assessment can be given each day. The procedure is easily adaptable for computer calculation, and because it is applied to individual cycles avoids the use of population means with the loss of information inherently associated with the combination of data from many cycles. The Trigg's tracking signal is an appropriate method of analysis of menstrual cycle data and represents a satisfactory alternative to the more usual cumulative sum procedure. The distribution of the first increases constitutes a reference standard for urinary estrogen assays.

Adult↗

PubMed1977

Creative productivity, age, and stress: a biographical time-series analysis of 10 classical composers.

The determinants of creative productivity were specified in the form of six hypotheses. Using a multivariate cross-sectional time-series design with several controls, the lives and works of 10 classical composers were analyzed into consecutive 5-year age periods. Two independent measures of productivity were operationalized (works and themes), with each measure subdivided into major and minor compositions according to a citation criterion. It was consistently found across both productivity measures that (a) quality of productivity is a probabilistic consequence of productive quantity and (b) total productivity, while affected by age and physical illness, is otherwise free of external influences (viz., social reinforcement, biographical stress, war intensity, and internal disturbances). Due to the more selective nature of the thematic productivity measure, the criterion of total themes alone was affected by competition and a time-wise bias. The article closes with a brief discussion of the broad substantive utility of the methodological design.

Adolescent↗

PubMed1978

The autoregressive time series modelling of stabilograms.

Power spectral density analysis of frontal and sagittal stabilograms in young male subjects with a normal vestibular function indicates the fitting of parametric time series models to stabilograms. Subjects were standing on a force platform under three different standing conditions. Stabilograms lasting for 2 minutes were processed by means of a TPAi computer with the CAMAC system. Following digital high-pass filtering, correlation functions and power spectral density distributions were estimated. Linear autoregressive models of increasing order up to 30 were fitted to stabilograms on the basis of the autocorrelation functions by means of a recursive scheme. The goodness of fit of the autoregressive models was significantly different in the standing conditions, planes and subjects. The orders of models for frontal stabilograms were higher than for sagittal ones, whereas the residual variances were lower than for sagittal stabilograms. We arrived at the conclusion that autoregressive modelling is a suitable approach for obtaining reliable spectral estimates and for characterizing the control system of body sway.

Humans↗