Methods for determining "reference changes" from serial measurements: plasma lipid-bound sialic acid.

1989 ◽  
Vol 35 (6) ◽  
pp. 972-974 ◽  
Author(s):  
S Shahangian ◽  
H A Fritsche ◽  
J I Hughes ◽  
D A Johnston
Keyword(s):  
Time Series ◽  
Sialic Acid ◽  
Healthy Subjects ◽  
Plasma Lipid ◽  
Autoregressive Time Series ◽  
The Mean ◽  
One Year ◽  
Mean Variance ◽  
Serial Measurements ◽  
Colorectal Adenocarcinomas

Abstract Lipid-bound sialic (neuraminic) acid (LSA) was measured in EDTA-treated plasma of 26 healthy subjects at three-month intervals for up to one year. The change in LSA concentration for consecutive measurements ranged from -54 to 42 mg/L (mean, -2.1 mg/L; SD, 19.6 mg/L; n = 56). The "reference change" for plasma LSA (+/- 2 SD), calculated from distribution of the differences, was +/- 39 mg/L. The 88th percentile of the intra-individual variance was 338 mg2/L2 and the mean variance was 159 mg2/L2. Using the homeostatic, autoregressive time-series model, a reference change of +/- 51 mg/L between two consecutive measurements was determined to be statistically significant (i.e., expected by chance no more than 5% of the time) in 88% of the healthy subjects. Only 73% of the healthy subjects would have had intra-individual variances corresponding to the reference change of +/- 39 mg/L according to the autoregressive model. The concentration of LSA in plasma was significantly decreased upon surgery in five of 10 patients with colorectal adenocarcinomas of Dukes stages A-C when we used +/- 39 mg/L as the reference change, but in only two of the 10 when we used +/- 51 mg/L as the reference change.

Plasma protein-bound sialic acid in patients with colorectal polyps of known histology

1991 ◽  
Vol 37 (2) ◽  
pp. 200-204 ◽  
Author(s):  
Shahram Shahangian ◽  
Herbert A Fritsche ◽  
John I Hughes ◽  
Richard S Foemmel ◽  
Nonda Katopodis
Keyword(s):  
Colorectal Cancer ◽  
Sialic Acid ◽  
Cancer Patients ◽  
Healthy Subjects ◽  
Mean Value ◽  
Colorectal Polyps ◽  
Hyperplastic Polyps ◽  
The Mean ◽  
Colorectal Cancer Patients ◽  
Colorectal Adenocarcinomas

Abstract Protein-bound sialic acid (PBSA) was measured in serial plasma specimens from 62 healthy subjects, 48 patients with colorectal polyps, and 30 patients with colorectal adenocarcinomas. The mean plasma PBSA concentration in healthy smokers was significantly greater than that in healthy nonsmokers and healthy ex-smokers (P less than 0.0001). Villoglandular polyps were associated with higher plasma PBSA values than were the most benign hyperplastic polyps (P less than 0.025). Patients with the most neoplastic villoglandular and villous polyps had significantly greater (P less than 0.010-0.050) plasma PBSA values than healthy subjects. Polypectomy decreased the mean PBSA value significantly to the mean value for healthy subjects only for patients with villoglandular (P less than 0.010) or villous (P less than 0.050) polyps. Colorectal cancer patients had mean plasma PBSA concentrations significantly greater than those for the healthy subjects (P much less than 0.001) and the polyp patients (P much less than 0.001). Surgery significantly reduced (P less than 0.025) the mean PBSA value for the cancer patients to the mean PBSA value observed for the healthy subjects.

Zooplankton Sample Variation on the Scotian Shelf

1978 ◽  
Vol 35 (9) ◽  
pp. 1207-1222 ◽  
Author(s):  
D. D. Sameoto
Keyword(s):  
Time Series ◽  
Fish Larvae ◽  
Geographic Area ◽  
Scotian Shelf ◽  
Tidal Cycles ◽  
Zooplankton Sample ◽  
Single Station ◽  
The Mean ◽  
One Year ◽  
Abundance And Distribution

Zooplankton sampling experiments on the Scotian Shelf during September 1973 and August 1974 using vertical tows demonstrated that numbers of many zooplankton species had a periodic fluctuation over 26 h. The fluctuations appeared related to the tide during 1974 but not in 1973. The periodic fluctuations accounted for a major portion of the sample variation in many species during both years. The mean numbers of small forms of zooplankton (copepods) obtained from the 26-h time series on a single station were very similar to means obtained during the same cruise over a wide area of the shelf. This suggested that a single station sampled over a period of two tidal cycles may be representative of the sample variation encountered over a wide geographic area of many hundreds of kilometres. Only Calanus and Pseudocalanus were correlated during all the experiments and from year to year. The abundance and distribution of the other species of zooplankton compared from one year to the next were not significantly correlated. This suggested the species populations were independent of one another. Key words: zooplankton, sample variation, time series, Scotian Shelf, fish larvae, Copepoda, tide

scholarly journals Une méthode asymptotique pour tester la validité du modèle d’équilibre d’actifs financiers (MEDAF) avec pour exemple la bourse de Paris

2009 ◽  
Vol 57 (2) ◽  
pp. 225-243
Author(s):  
Emmanuel Apel
Keyword(s):  
Time Series ◽  
Sample Size ◽  
Stock Exchange ◽  
Rate Of Return ◽  
Residual Variance ◽  
Cross Sectional ◽  
Market Portfolio ◽  
The Mean ◽  
Squared Residuals ◽  
Mean Variance

ABSTRACT One of the problems in testing the validity of the two-parameter CAPM is the determination of an efficient proxy market portfolio to represent the true market portfolio. We test the mean-variance efficiency of a pre-specified market portfolio by using a method proposed by Roll (1976) for testing the linear relation between the rate of return of an asset and its beta, and hence the mean-variance efficiency of a proxy market portfolio. This procedure exploits the asymptotic exact linearity condition of the rate of return and beta by measuring the rate of decrease of cross-sectional residual variance with respect to increasing time-series sample size. The technique is applied to samples of companies on the Paris Stock Exchange for the period 1969-1978: 144 companies and twenty-nine different time series. The results indicate that although the sum of the squared residuals of a CAPM-type regression declines as the number of time observations increases, the sum of the squared residuals does not approach zero as the temporal sample size increases, as would be required for the market proxy of our pre-specified sample to be efficient.

scholarly journals Time Series Analysis of Mean Monthly Temperature in the Far Western Ethiopia, Assosa District

2020 ◽  
Author(s):  
Tigabu Hailu Kassa ◽  
Shewayiref Geremew Gebremichael
Keyword(s):  
Time Series ◽  
Arima Model ◽  
Descriptive Statistics ◽  
Mean Annual Temperature ◽  
Temperature Pattern ◽  
First Order ◽  
Monthly Temperature ◽  
The Mean ◽  
One Year ◽  
Western Ethiopia

Abstract BackgroundThis study investigated the mean monthly temperature pattern of the Assosa district, Western Ethiopia. The objective of this study was to analyze the mean monthly temperature patterns in the Assosa district for the period from January 2012 to December 2016 based on data from meteorological stations in the Assosa district.MethodsDescriptive statistics and univariate Box-Jenkins methodology to build the seasonal ARIMA model were used.ResultsThe results showed that the mean annual temperature of Assosa was 28.025 degree Celsius. The original series was found to be seasonally non-stationary, as indicated by the ACF plot of the series. After using first-order seasonal differencing, the series was found to be stationary. A time-series model for the Assosa station was adjusted, processed, diagnostically checked, and finally, an ARIMA (3.0.1) model is established and this model is used to forecast one-year mean monthly temperature values. ConclusionThe forecasted mean temperature values showed a similar pattern to previous recordings.

scholarly journals Time-variability of the fraction of young water in a small headwater catchment

2019 ◽  
Author(s):  
Michael P. Stockinger ◽  
Heye R. Bogena ◽  
Andreas Lücke ◽  
Christine Stumpp ◽  
Harry Vereecken
Keyword(s):  
Time Series ◽  
Time Window ◽  
High Sensitivity ◽  
Annual Runoff ◽  
Nutrient Loss ◽  
Time Variability ◽  
Short Term ◽  
Sampling Campaign ◽  
The Mean ◽  
One Year

Abstract. The time precipitation needs to travel through a catchment to its outlet is an important descriptor of a catchment's susceptibility to pollutant contamination, nutrient loss and hydrological functioning. The fast component of total water flow can be estimated by the fraction of young water (Fyw) which is the percentage of streamflow younger than three months. Fyw is calculated by comparing the amplitudes of sine waves fitted to seasonal precipitation and streamflow tracer signals. This is usually done for the complete tracer time series available neglecting annual differences in the amplitudes of longer time series. Considering inter-annual amplitude differences, we here employed a moving time window of one-year length in weekly time steps over a 4.5-years δ18O tracer time series to calculate 189 Fyw results. The results were then tested against the following null hypotheses, defining 2 % difference in Fyw as significant based on results of previous studies: (1) Fyw does not deviate more than ±2% from the mean of all Fyw results indicating long-term invariance. Larger deviations would indicate either flow path changes or a change in the relative contribution of different flow paths; (2) for any four-week window Fyw does not change more than ±2 % indicating short-term invariance. Larger deviations would indicate a high sensitivity of Fyw to a 1–4 weeks shift in the start of a one-year sampling campaign; (3) for a given calendar month Fyw does not change more than ±2 % indicating seasonal invariance of Fyw. In our study, all three null hypotheses were rejected. Thus, the Fyw results were time-variable, showed a high variability in the chosen sampling time and had no pronounced seasonality. Based on high short-term variability of Fyw when the mean adjusted R² was below 0.2 we recommend that a low R2 should be regarded as indicating potentially highly uncertain Fyw results. Furthermore, while investigated individual meteorological factors could not sufficiently explain variations of Fyw, the runoff coefficient showed a moderate negative correlation of r = −0.54 with Fyw. This indicated that when annual runoff exceeded precipitation the catchment received the water deficit from storage which is old water causing a decrease in Fyw. The results of this study suggest that care must be taken when comparing Fyw of catchments that were based on different calculation time periods.

scholarly journals Robustness of Forecasting for Autoregressive Time Series with Bilinear Distortions

2016 ◽  
Vol 37 (1) ◽  
Author(s):  
Yuriy Kharin ◽  
Olga Radzieuskaya
Keyword(s):  
Time Series ◽  
Time Series Model ◽  
Mean Square ◽  
Autoregressive Time Series ◽  
Risk Criterion ◽  
The Mean ◽  
Stochastic Time Series ◽  
Stochastic Time

The paper is devoted to the investigation of bilinear stochastic time series model BL(p, 0, 1, 1). The linear autoregressive forecasting statistic is considered under the mean-square risk criterion; its robustness under bilinear distortions is evaluated.

Influence of Platelet Membrane Sialic Acid and Platelet-Associated IgG on Ageing and Sequestration of Blood Platelets in Baboons

1993 ◽  
Vol 70 (04) ◽  
pp. 676-680 ◽  
Author(s):  
H F Kotzé ◽  
V van Wyk ◽  
P N Badenhorst ◽  
A du P Heyns ◽  
J P Roodt ◽  
...  
Keyword(s):  
Sialic Acid ◽  
Life Span ◽  
Blood Platelets ◽  
Senescent Cell ◽  
Platelet Membrane ◽  
Antigen Complex ◽  
The Mean ◽  
Aggregation Of Platelets

SummaryPlatelets were isolated from blood of baboons and treated with neuraminidase to remove platelet membrane sialic acid, a process which artificially ages the platelets. The platelets were then labelled with 111In and their mean life span, in vivo distribution and sites of Sequestration were measured. The effect of removal of sialic acid on the attachment of immunoglobulin to platelets were investigated and related to the Sequestration of the platelets by the spleen, liver, and bone marrow. Removal of sialic acid by neuraminidase did not affect the aggregation of platelets by agonists in vitro, nor their sites of Sequestration. The removal of 0.51 (median, range 0.01 to 2.10) nmol sialic acid/108 platelets shortened their life span by 75 h (median, range 0 to 132) h (n = 19, p <0.001), and there was an exponential correlation between the shortening of the mean platelet life span and the amount of sialic acid removed. The increase in platelet-associated IgG was 0.112 (median, range 0.007 to 0.309) fg/platelet (n = 25, p <0.001) after 0.79 (median, range 0.00 to 6.70) nmol sialic acid/108 platelets was removed (p <0.001). There was an exponential correlation between the shortening of mean platelet life span after the removal of sialic acid and the increase in platelet-associated IgG. The results suggest that platelet membrane sialic acid influences ageing of circulating platelets, and that the loss of sialic acid may have exposed a senescent cell antigen that binds IgG on the platelet membrane. The antibody-antigen complex may then provide a signal to the macrophages that the platelet is old, and can be phagocytosed and destroyed.

EFFECTS OF SYNTHETIC LH/FSH-RELEASING HORMONE (LRH) ON PLASMA LH AND FSH IN AMENORRHOEIC WOMEN

1974 ◽  
Vol 75 (4) ◽  
pp. 647-652 ◽  
Author(s):  
G. Rannevik ◽  
J. Thorell
Keyword(s):  
Urinary Excretion ◽  
Initial Response ◽  
Releasing Hormone ◽  
The Mean ◽  
The Difference ◽  
Serial Measurements

ABSTRACT Eight amenorrhoeic women were given 100 μg synthetic LRH (Hoechst) iv and im, respectively, at an interval of 2 weeks. Four of the women received the iv injection first and four the im injection. The urinary excretion of oestrogens and pregnanediol was low and unaltered throughout the test weeks. The effects of LRH were compared by serial measurements of the plasma LH and FSH during 8 h. The initial response of LH for up to 25 min and that of FSH for up to 60 min were equal whether LRH was given iv or im. The difference appeared later. Four hours after the injection the mean increase of LH to iv injection was 0.5 ng/ml (N. S.), while that to im injection was 1.9 ng/ml (P < 0.01). The corresponding values for FSH were 1.3 (P < 0.05) and 3.2 (P < 0.001). The effect of LRH administration im was thus found to be larger and more prolonged.

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