SEARCH · PubMed Health

Results for “Time series analysis”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 recordsLinked to original sources

PubMed1991

[Demographic and economic trends in medical schemes--a time series analysis].

A time series analysis was performed on medical scheme statistics with the aim of determining current and future demographic and economic trends. This would enable one to reach a better perspective on the current and future financial dilemma presently experienced by medical schemes. Data for the period 1978-1986 was analysed on a computer, using the Statgraphics program. The linear trend projection method, based on the regression analysis technique was used. Real values were determined by deflating nominal values against the consumer price index with 1980 as base year. There are at present 253 medical schemes in operation. Approximately 16 per cent of the economically active population are members of medical schemes. White members increased by only 3.8 per cent during the period 1978-1986, in comparison to the 87.1 per cent by black members. The beneficiaries represent 19 per cent of the total population; black beneficiaries increased by 422.1 per cent, while Whites increased only fractionally by 0.73 per cent. Membership fees increased by an average of R8.08/member/month or R1.72/member/month in real terms. Ninety five per cent of the income of medical schemes was derived from membership fees. The average real growth rate of income was 8.4 per cent, while net assets increased by only 3 per cent. An average deficit of R11.02 million/year is estimated for the recommended reserve funds in real terms. The greatest proportion of benefits paid was for professional services (47.4 per cent) followed by medicine (26.3 per cent) and hospital services (19.8 per cent). The real growth rate for benefits paid was 8.6 per cent per year.(ABSTRACT TRUNCATED AT 250 WORDS)

Economics↗

PubMed1990

Dynamic changes in cardiac vagal tone as measured by time-series analysis.

A time-series analysis of heart rate variability was evaluated as a marker of cardiac vagal tone using well-characterized autonomic interventions. Heart period (R-R interval) was recorded in 14 mongrel dogs from which the amplitude of the respiratory sinus arrhythmia (0.24-1.04 Hz) was determined. Exercise elicited significant (P less than 0.01) reductions in the index of vagal tone (control 6.3 +/- 0.3 ln ms2 vs. exercise 2.4 +/- 0.4 ln ms2) that were accompanied by significant (P less than 0.01) increases in heart rate (control 123.1 +/- 5 vs. exercise 201.0 +/- 7.7 beats/min). The vagal tone index remained greater than 0 throughout exercise. After propranolol HCl pretreatment, the vagal tone index rapidly decreased toward zero (control 6.2 +/- 0.5; exercise 0.7 +/- 0.3 ln ms2), despite significantly lower increases in heart rate (control 109.3 +/- 4.2; exercise 178.0 +/- 7.6 beats/min). Atropine given during exercise evoked significantly greater increases in heart rate in the control (+48.7 +/- 7.9 beats/min) vs. propranolol (+14.2 +/- 6.7 beats/min) conditions. These data suggest that 1) high levels of cardiac vagal tone remain during exercise; 2) vagal withdrawal is largely responsible for the heart rate increase after beta-adrenergic receptor blockade; and 3) time-series analysis of the R-R interval can provide a dynamic and noninvasive index of cardiac vagal tone.

Adrenergic beta-Antagonists↗

PubMed1990

The treatment of tension headache by acupuncture: a controlled single case design with time series analysis.

A single case design, with time series analysis, was employed to evaluate the efficacy of acupuncture in the treatment of tension headache. Fourteen patients were given eight weekly treatments, four of true acupuncture and four of sham in random order. Mean pain in medication scores were reduced by 52% and 54% respectively at initial follow-up. Reductions in pain scores of over 50% were achieved by half the patients and the significance of these changes confirmed by time series analysis. The majority of patients maintained their gains at four month follow-up. True acupuncture was shown to be significantly superior to sham, demonstrating a specific therapeutic action, in four patients. In the remainder no difference was observed. Possible mechanisms for these effects are discussed. Acupuncture is a potentially valuable treatment for tension headache but further research is needed.

Acupuncture Analgesia↗

PubMed1991

Time series analysis of knowledge of results effects during motor skill acquisition.

Time series analysis was used to investigate the hypothesis that during acquisition of a motor skill, knowledge of results (KR) information is used to generate a stable internal referent about which response errors are randomly distributed. Sixteen subjects completed 50 acquisition trials of each of three movements whose spatial-temporal characteristics differed. Acquisition trials were either blocked, with each movement being presented in series, or randomized, with the presentation of movements occurring in random order. Analysis of movement time data indicated the contextual interference effect reported in previous studies was replicated in the present experiment. Time series analysis of the acquisition trial data revealed the majority of individual subject response patterns during blocked trials were best described by a model with a temporarily stationary, internal reference of the criterion and systematic, trial-to-trial variation of response errors. During random trial conditions, response patterns were usually best described by a "White-noise" model. This model predicts a permanently stationary, internal reference associated with randomly distributed response errors that are unaffected by KR information. These results are not consistent with previous work using time series analysis to describe motor behavior (Spray & Newell, 1986).

Adolescent↗

PubMed1991

Environmetric time-series analysis: modelling natural systems from experimental time-series data.

Using the modelling of solute transport in flowing media as an example, this paper outlines the main aspects of a systematic approach to the modelling of natural systems from experimental time-series data. The objective of the approach, which exploits sophisticated methods of recursive parameter estimation, is to produce a parametrically efficient, data-based model which is both physically meaningful and statistically well defined. Although the proposed methodology has its origins in systems and control theory and may be unfamiliar to some natural scientists, it has been developed and refined for use with natural environmental systems over the past 20 years, and has wide application potential in areas such as biology and ecology. In this sense, the paper is intended to introduce the more general reader to the topic, in the hope that the tutorial review and practical examples will stimulate interest and encourage reference to the many publications cited in the paper. The practical examples are concerned with the modelling of pollutant dispersion in stream channels: phloem translocation and carbon partitioning in plants: and rainfall-streamflow modelling in a river catchment.

Algorithms↗

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↗

PubMed1991

Responders and non-responders to metoprolol, propranolol and nifedipine treatment in migraine prophylaxis: a dose-range study based on time-series analysis.

The aim of the present study was to ascertain, on the basis of single case statistics and time-series analysis, responder and non-responder rates for metoprolol, propranolol and nifedipine in migraine prophylaxis. In addition, an attempt was made to identify the dose relationship for the various drugs on headache parameters. In a double-blind dose-finding study, 58 patients were treated in five consecutive dosage steps each lasting 1-3 months. All patients kept a headache diary before, during and after treatment. Serum drug levels were also determined. The data were assessed by time-series analysis, as well as by multiple regression and analysis of variance. A significant improvement was noted in 54.4% of patients with migraine during treatment with metoprolol. The study did not confirm the high success rates in migraine prophylaxis of nifedipine and propranolol quoted in the literature. Administration of nifedipine led to an increase in migraine attacks in 71% of the patients. Nifedipine was of no value in the prophylaxis of migraine. Only 32% of patients showed a reduction in frequency of migraine attacks during administration of propranolol. The analysis of variance failed to show any significant difference between the responder rates for metoprolol and propranolol. Higher doses of propranolol and metoprolol were more effective. Multiple regression analysis explained a considerable part of variance for propranolol (but not for metoprolol) as a result of reduced intake of ergotamine preparations and analgesics. It can therefore be concluded that part of the prophylactic effect of propranolol is attributable to a reduction in the use of migraine medication.

Adolescent↗

PubMed1990

The dramatic increase in the rate of low birthweight in New York City: an aggregate time-series analysis.

This paper uses monthly time-series data from 1968 through 1988 to test whether the observed increase in the incidence of low birthweight in New York City represents a reversal of the downward trend that existed prior to 1984. We find that the trend has shifted for both Whites and Blacks. We estimate that between July 1984 and December 1988 there were 3,110 additional low-birthweight births to Blacks and 1,385 additional low-birthweight births to Whites above what would have been expected had the rate of low birthweight not shifted upwards. The incremental costs of treating these infants in their first year of life is estimated at over $22,000,000 in 1986 dollars.

Black People↗

PubMed1991

Time series analysis of obsessional behavior and mood during self-imposed delay and response prevention.

Time series analysis of more than a year of daily self-report of three subjects showed that self-imposed delay and response prevention was effective in decreasing obsessions and compulsions. The subject-controlled treatment had a varied effect on mood-anxiety decreased in two subjects, but depression increased in one. (A similar worsening of mood after elimination of obsessional behavior was found in a previous case study.) Apparently, successful treatment of obsessional behavior will not necessarily lead to an improvement in mood. Concurrent mood symptoms need to be targeted separately; and, plans should be made to deal with mood symptoms that may occur once obsessional behavior is removed.

Adolescent↗

PubMed1990

Time-series analysis. Use of autocorrelation as an analytic strategy for describing pattern and change.

Although graphic representation of time-series data is one method to describe patterns of phenomena, autocorrelations, correlograms, and plots of the autocorrelation function provide descriptive and statistical methods that reveal the structure of a deterministic cycle component within the time-series. The autocorrelation function provides a method for the investigator to test hypotheses about the nature and pattern of relationships between measured and latent variables. Patterns of phenomena can be analyzed statistically using objectively provided criteria. The autocorrelation function can also be used to understand the change in response or behavioral patterns following an experimental intervention. Traditional group comparison designs, using cross-sectional data collection strategies cannot identify differences within the individual nor can they identify patterns of behavior or structural patterns within the data. Autocorrelation and cross-correlation become threats to statistical validity when conventional methods are used; however, in time-series analysis, autocorrelation allows close scrutiny of the pattern of response within an individual across a time-dimension.

Data Interpretation, Statistical↗

PubMed1992

Fertility and suicide rates: a time series analysis in the United States.

In a time series study of the USA from 1933 to 1984, fertility rates were associated with the suicide rates of those aged 15-44. The higher the fertility rate the lower the suicide rate for these age groups, for both whites and non-whites, and for both men and women. The results were seen as supporting Durkheim's theory of suicide.

Adolescent↗

PubMed1992

[Time-series analysis applied to nosocomial infection].

BACKGROUND: In this study we introduce a new view of hospital infection, to apply time series techniques to it. Our objective is to complement hospital infection's epidemiological surveillance by means of obtaining alert and alarm thresholds that make easy to the epidemiologist the decision of intervention, in case they are exceeded. METHODS: We have used the classic time series analysis described by Rumeau-Rouquette, and ARIMA (Autoregresive Integrated Moving Average) models developed by Box and Jenkins. The study focus on three hospital units: one intensive care, one long term care and one surgical unit. The nosocomial infection intervals have been calculated with a 68% (1SD) and 95% (2SD) confidence levels. RESULTS: We detect an ascending general trend in the last two units, without the detection of seasonal variations. Two ARIMA (1, 0, 0) models we obtained for surgery and long term care, discarding other better adjusted models, more complex and difficult to obtain, but with no real advantage in prediction power. Confidence intervals were calculated with both methods. We did not find general trend and seasonal variations for intensive care unit. No model was considered valid, because of its high random component. The nosocomial infection intervals have been calculated with mean +/- 1SD and mean +/- 2SD. CONCLUSIONS: We think that more precise knowledge of hospital infection, with a high random component in our study, can be in addition useful to assign priority to human and material resources.

Analysis of Variance↗

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↗

PubMed1990

Time-series analysis--spectral analysis and the search for cycles.

In summary, spectral analysis is one analytic strategy for analyzing time-series data. Specifically, spectral analysis enables researchers to detect cyclicity and determines the variance in the data accounted for by cyclic activity. Results describe cycle frequency, period, and amplitude. Unlike cosinor analysis (Lentz, 1990b), spectral analysis does not directly determine peak time nor directly indicate time-ordered relationships, as does autocorrelation (Taylor, 1990). Cyclic relationships between time-series data can be detected using coherency (Gottman & Ringland, 1981), an extension of spectral analysis which is beyond the scope of this article. A word of caution is in order for the uninitiated researcher. Spectral analysis, as well as autocorrelation and cosinor analysis, entails within-subject analysis of single variables. Currently, means of determining relationships between time series, such as cross-correlation and coherency, are bivariate. The need to analyze the pattern of individual variables within-subject, followed by examination of bivariate relationships between pairs of variables, is wisely balanced by limited numbers of variables and small sample size.

Nursing Research↗

PubMed1990

Application of time series analysis to circadian rhythms: effect of beta-adrenergic blockade upon heart rate and transient myocardial ischemia.

Circadian variations of transient myocardial ischemia and heart rate have been identified, but the rhythms and their response to beta blockade have not been fully characterized. Time-series analysis, a mathematical technique to describe oscillatory activity occurring within a continuous data set was used, to address these issues. Nine men with coronary artery disease underwent 72 hours of ambulatory electrocardiographic monitoring during therapy with placebo or metoprolol. During administration of placebo, ischemic time and heart rate showed a primary peak with a periodicity of approximately 24 hours with a tight coupling between the 2 variables and a secondary peak with a periodicity of 5 to 8 hours. During metoprolol therapy, heart rate and ischemic variation were reduced and the 24-hour periodicity for heart rate only remained. The 24-hour periodicity for ischemia was eliminated, but the data with 5- to 8-hour periodicity became the major component of the signal.

Angina Pectoris↗

PubMed1991

A time-series analysis of longitudinal weight changes in two adult women.

This study was conducted to examine individual longitudinal serial trends in body weight of two moderately obese adult women. Self-measured daily weights (over 5000 data points for subject 1 and over 3500 for subject 2) were averaged for each month and analyzed using a time-series analysis approach. The best statistical model for both women indicated a significant upward trend (gain 30 and 22 lb, respectively) interrupted by linear decreases (P less than 0.05) during weight loss programs over the 16- and 10-year observation periods, respectively. The women participated in six and eight weight control programs, respectively, and consistently lost weight, averaging 9.17 +/- 1.85 lb and 8.00 +/- 3.57 lb. Both subjects regained weight after dieting, in a period approximately 2.25 times as long as the diet. Numerous weight fluctuations occurred and one subject lost and then regained 10 percent of her body weight during two 5-year periods. Results are examined in terms of a possible weight increase protection benefit, as well as the deleterious medical potential that may occur with numerous weight loss attempts. Suggestions for future research are provided regarding weight cycling, seasonal variations, set point theory, aging effects, and the use of self-directed weight loss initiatives in conjunction with formal weight reduction programs. This study may serve as a prototype for exploring weight fluctuation using time-series analyses and for further investigating the etiology and clinical management of obesity.

Body Mass Index↗

PubMed1990

Time-series analysis of myoelectric cycling of sphincter of Oddi: evidence of cycling during fed state.

The sphincter of Oddi (SO) in the fasted opossum exhibits spontaneous cyclic spikeburst activity that is temporally related to the interdigestive migrating myoelectric complex (MMC) of the small intestine. After feeding, the cyclic activity is apparently disrupted. Our aim was to use time-series analysis to mathematically describe the periodic behavior of the fasted state and to determine whether this periodicity is present after feeding. Five opossums were chronically prepared with bipolar electrodes secured to the SO. With the animals fasted and conscious, myoelectric activity was recorded for at least two MMC cycles after which they were fed 170 kcal of cream. Spikeburst frequency data were analyzed by fast Fourier transform (FFT) and by digital band-pass filtering. Results from FFT analysis showed an intense low-frequency peak during the fasted state which persisted but was markedly depressed during the fed state. Analysis of the data after filtering also showed persistent sinusoidal activity at the MMC frequency after feeding, although the waveform was significantly depressed by both peak-to-peak amplitude and root mean square amplitude analysis. Recovery to normal fasting cyclic behavior with recovery of both FFT and filtered data was observed. We conclude that in the opossum the cyclic nature of the SO myoelectric activity observed during the fasted state persists after feeding, but is inhibited and masked by an increase in overall spikeburst activity.

Ampulla of Vater↗

PubMed1978

Crisis intervention and the prevention of institutionalization: an interrupted time series analysis.

In the context of the community mental health movement in Illinois, the evolution and development of a crisis intervention program aimed at avoiding state hospitalization and bringing more appropriate and efficacious resources to bear on the difficulties of the individual and/or family is described. This intervention program is characterized by a more active-seeking style of delivering mental health services. With the novel application of interrupted time series analysis to both the targeted and matched nonequivalent control communities the efficacy of this more active intervention in reducing the number of state hospital administrations diagnosed as "mentally ill" is highlighted. The cost/benefit to the taxpayer is also discussed.

Community Mental Health Services↗