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Results for “Population Size--statistics”

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PubMed1999

Statistical power of MRI monitored trials in multiple sclerosis: new data and comparison with previous results.

OBJECTIVES: To evaluate the durations of the follow up and the reference population sizes needed to achieve optimal and stable statistical powers for two period cross over and parallel group design clinical trials in multiple sclerosis, when using the numbers of new enhancing lesions and the numbers of active scans as end point variables. METHODS: The statistical power was calculated by means of computer simulations performed using MRI data obtained from 65 untreated relapsing-remitting or secondary progressive patients who were scanned monthly for 9 months. The statistical power was calculated for follow up durations of 2, 3, 6, and 9 months and for sample sizes of 40-100 patients for parallel group and of 20-80 patients for two period cross over design studies. The stability of the estimated powers was evaluated by applying the same procedure on random subsets of the original data. RESULTS: When using the number of new enhancing lesions as the end point, the statistical power increased for all the simulated treatment effects with the duration of the follow up until 3 months for the parallel group design and until 6 months for the two period cross over design. Using the number of active scans as the end point, the statistical power steadily increased until 6 months for the parallel group design and until 9 months for the two period cross over design. The power estimates in the present sample and the comparisons of these results with those obtained by previous studies with smaller patient cohorts suggest that statistical power is significantly overestimated when the size of the reference data set decreases for parallel group design studies or the duration of the follow up decreases for two period cross over studies. CONCLUSIONS: These results should be used to determine the duration of the follow up and the sample size needed when planning MRI monitored clinical trials in multiple sclerosis.

Adolescent↗
PubMed2003

Multimodal particle size distributions emitted from HFA-134a solution pressurized metered-dose inhalers.

The purpose of this research was to investigate the measurement and in vitro delivery implications of multimodal distributions, occurring near or in the respirable range, emitted from pressurized metered-dose inhalers (pMDIs). Particle size distributions of solution pMDIs containing hydrofluoroalkane-134a (HFA-134a) and ethanol were evaluated using 2 complementary particle-sizing methods: laser diffraction (LD) and cascade impaction (CI). Solution pMDIs were formulated from mixtures of HFA-134a (50%-97.5% wt/wt) and ethanol. A range of propellant concentrations was selected for a range of vapor pressures. The fluorescent probe, Rhodamine B, was included for chemical analysis. The complementary nature of LD and CI allowed identification of 2 dominant particle size modes at 1 and 10 micro m or greater. Increasing propellant concentrations resulted in increases in the proportion of the size distributions at the 1- micro m mode and also reduced the particle size of the larger droplet population. Despite significant spatial differences and time scales of measurement between the particle-sizing techniques, the fine particle fractions obtained from LD and CI were practically identical. This was consistent with LD experiments, which showed that particle sizes did not decrease with increasing measurement distance, and may be explained by the absence of significant evaporation/disintegration of larger droplets. The fine particle fractions (FPFs) emitted from HFA-134a/ethanol solution pMDI can be predicted on the basis of formulation parameters and is independent of measurement technique. These results highlight the importance of presenting particle size distribution data from complementary particle size techniques.

Aerosols↗
PubMed2004

Centile charts II: alternative nonparametric approach for establishing time-specific reference centiles and assessment of the sample size required.

BACKGROUND: Reference intervals, and more generally centile estimates, are used to characterize a reference population for the purposes of interpreting an individual patient's clinical measurement. We describe methods of calculating reference intervals where these centiles vary with a covariate, usually age or time. METHODS: The US Food and Drug Administration and the IFCC have made recommendations on two approaches: the parametric approach, which models the structural characteristics of the data set with a theoretical distribution, and the nonparametric approach, which makes no particular assumption about this structure. In this report we propose a nonparametric procedure that relies on the principles of regression and show how sample size determination can be assessed. We also show how the sample size calculation is influenced by the distribution of the times measured. RESULTS: We illustrated our method on three data sets and compared the results for our proposed nonparametric method with parametric estimates. We showed that the bias is reduced and that the nonparametric method is less likely to produce fluctuating profiles. CONCLUSIONS: To achieve adequate precision the sample size needs to be larger than 120, as has often been recommended. If there is doubt about the parametric model, then threshold sample sizes may need to be as high as 500.

Adolescent↗
PubMed2000

Examination of hemolytic potential with the On-X(R) prosthetic heart valve.

BACKGROUND AND AIM OF THE STUDY: Mechanical valves are known to produce chronic, subclinical hemolysis in most patients. Generally, haptoglobin is reduced to below normal in most patients, while lactate dehydrogenase (LDH) is increased to as much as 200% above the upper normal, sometimes resulting in anemia. The study was designed to investigate the clinical hemolysis of the On-X(R) prosthetic heart valve in a multicenter experience with a standard protocol and a single clinical laboratory. METHODS: Between September 1996 and August 1998, 248 patients underwent isolated valve replacement at 10 European centers. Blood samples were collected from these preoperatively and at 3-6 months and one year postoperatively. All samples were analyzed at a central laboratory, thus assuring poolability of the data. In total, 151 patients were tested at 3-6 months, and 62 at one year. Blood parameters measured were LDH, haptoglobin, hematocrit, total hemoglobin, red cell count and reticulocyte count. Paired analysis was used to compare preoperative baseline values with 3-6-month and one-year values. Data were analyzed with regard to both valve position and size. RESULTS: At 3-6 months and one year after surgery, average values for hematocrit, hemoglobin, red cell count and reticulocyte count were all near the center of the normal range, regardless of valve position or size. Statistically significant increases in red cell count and decreases in reticulocyte count occurred after both aortic valve replacement (AVR) and mitral valve replacement (MVR). These changes were of no clinical importance, but indicate that anemia has not occurred in these patients. At 3-6 months, haptoglobin was reduced to below normal in 86% of both AVR and MVR patients; this also occurred after one year and was statistically significant. Postoperatively, the mean LDH value in AVR was 228 U/l (91% of upper normal, 250 U/l) at 3-6 months, and 246 U/l (98% of upper normal) at one year. In MVR, these LDH values were 271 U/l (108% of upper normal) and 265 U/l (106% of upper normal). CONCLUSIONS: These results indicate that the On-X valve causes lower levels of chronic hemolysis in the immediate postoperative period and up to one year after surgery, especially when compared with reports of LDH elevations up to 200% of upper normal. Hemolytic anemia has not occurred in this patient population.

Aortic Valve↗
PubMed1981

Families in Israel, 1980.

This publication "presents data on families (households) in Israel for the year 1980. The data are based on the series of civilian Labour Force Surveys conducted since 1954, and relate to the characteristics of families in Israel with regard to size of family, population group, age, continent of birth, years of schooling, type of locality of residence and sex of family head."

Age Factors↗
PubMed1978

Age at marriage.

Explore the source record for details and available documents.

Age Factors↗
PubMed1993

[Demographic review of the Netherlands, 1992].

Demographic trends in the Netherlands during 1992 are reviewed. Among the findings, the author notes that "in 1992 the Dutch population grew by 110 thousand.... The number of births fell by some 2 thousand, immigration by 3.5 thousand. The number of deaths remained unchanged. Emigration increased by 1.5 thousand.... Twelve per cent of the population live in a one person household. Thirty years ago this was only 3%. Due to the decreased average number of children per family the proportion of children fell from 44% in 1960 to 30% in 1992. The number of people who were born abroad shows an annual growth of 4.4%. The growth of the native population is 0.44% per year.... Fertility is highest for 30 year old women. In 1970 this was the case for those who were 26 years of age." (SUMMARY IN ENG)

Age Factors↗
PubMed1991

Problem of weights in the analysis of demographic phenomena in territorial arrangement.

The author attempts to eliminate the influence of the size of a territorial unit on the results of demographic analysis, using data for Poland as an illustration. She concludes that "the inclusion of weights in statistical analysis allows us to eliminate the impact of the sizes of studied units on the values of counted parameters as well as on the measures of correlation and regression. The existence of a close connection between the results obtained and the sizes of the studied groups within the same population should be always taken into account."

Developed Countries↗
PubMed1992

[Detection of the safety depth on human chest by computer tomographic scanning].

Knowledges of acupuncture has played a major role in the treatment of human diseases, and has been mentioned in ancient Chinese medical literature for thousands of years. The loci which are most commonly used as treatment sites are points on the Ren Channel, kidney Channel, Stomach Channel, Pericardium Channel, Lung Channel, Spleen Channel and Gallbladder Channel for those loci on the human chest, insertion depth beyond safety level, can create serious consequences other such as pneumothorax, internal organ bleeding or other damage. This study was designed to determine the real safety depth for each locus by using a current scientific approach. The study was carried out at Tri-Service General Hospital and Mackay General Hospital. The sample patient population was 120. According to their body weight and height, patients were divided into six groups with various body sizes, i.e. normal, over and under-weight adults, and by sex differences. After computer tomographic scanning chest, the relative acupuncture loci should be measured according to anatomical position, then the distance between surface of the chest and thoracic pleura can be defined as its safety depth. For each locus of the groups, the mean and its interval of confident can be found. The analysis of variance (ANOVA), t-test, and multiple regression were also calculated by computer. The results show that there are significant differences in body chest loci within the same sex but, for different body sizes, statistically significant differences for each locus appear, so the safety depth for each chest locus has actually been proved. Not only does his data provide useful information for clinical practices, but also the standard safety depth for each loci on the chest could this be established.

Acupuncture Points↗
PubMed2004

A new quality control method based on a moving average of "latent reference values" selected from patients' daily test results.

The average of normals(AON) method is a quality control(QC) method that uses measured values of patients' samples instead of QC samples. Because this method is easily affected by fluctuations in the patient population and is insensitive to short-term changes in test values, we developed an alternative method based on the moving average(MA) of latent reference values(LRVs) which are the test results of patients whose other related test results are all within reference intervals. We evaluate the new methodology(MALRV) using seven commonly measured biochemical tests. The LRV of each test were selected with reference to four other items that had the highest coincidences of abnormality. The optimum amount of data needed to compute the MA is determined as that making the coefficient of variation(CV) of the consecutive MA over a study period less than 5.0%. The MALRV is computed each time a new LRV is encountered to monitor quality status continuously. The MALRV CV was within 5.0% when sample sizes were between 20 and 110. When shift and trend simulations were performed with the patient data, the corresponding alterations were detected. MALRV is a useful measure for detecting short-term alterations in patient test results, supplementing the conventional QC chart method.

Clinical Laboratory Techniques↗