Comparaison de différentes approches, modèles et tailles d'échantillons pour l'établissement de relations hauteur-diamètre locales

1995 ◽  
Vol 25 (8) ◽  
pp. 1303-1312 ◽  
Author(s):  
Jean Bégin ◽  
Frédéric Raulier
Keyword(s):  
Sample Size ◽  
Residual Variance ◽  
Sample Plot ◽  
Sample Sizes ◽  
Total Height ◽  
Breast Height ◽  
Mean Diameter ◽  
The Mean ◽  
The Individual ◽  
Model Approach

This study compares the predictability of 3 approaches, 4 models, and 10 different sample sizes to determine local relationships between total height and diameter at breast height in balsam fir stands less than 50 years old. The results show that a system of height–diameter curves based on the mean diameter and mean height of the sampled trees (approach 3) gives the most precise estimations in comparison with curves resulting from pooling all sampled trees in a single height–diameter model (approach 1) and with those resulting from the application of a height–diameter model for each of the combinations of sample plot–measurement periods (approach 2). Depending on the sample size, the residual variance of the total height or the total volume is reduced 2 to 2.5 times for the individual stems and 2 to 15 times for the mean stem, when using approach 3 instead of approach 1. Approach 3 is more precise than approach 2 for sample sizes that vary between three and five sampled trees per plot. However, this gain in precision becomes negligible when the sample size approaches 10 sampled trees per plot.

scholarly journals The Probability That a Measurement Falls within a Range of Standard Deviations from an Estimate of the Mean

2012 ◽  
Vol 2012 ◽  
pp. 1-8 ◽  
Author(s):  
Louis M. Houston
Keyword(s):  
Confidence Interval ◽  
Sample Size ◽  
General Equation ◽  
Sample Sizes ◽  
The Mean ◽  
Standard Deviations ◽  
Intermediate Value ◽  
Theoretical Results

We derive a general equation for the probability that a measurement falls within a range of n standard deviations from an estimate of the mean. So, we provide a format that is compatible with a confidence interval centered about the mean that is naturally independent of the sample size. The equation is derived by interpolating theoretical results for extreme sample sizes. The intermediate value of the equation is confirmed with a computational test.

scholarly journals Modelling Bark Thickness of Norway Spruce (Picea abies Karst)

2019 ◽  
Vol 10 (2) ◽  
pp. 125-135
Author(s):  
Jusuf Musić ◽  
Velid Halilović ◽  
Jelena Knežević ◽  
Admir Avdagić ◽  
Aida Ibrahimspahić ◽  
...  
Keyword(s):  
Norway Spruce ◽  
Bosnia And Herzegovina ◽  
Timber Harvesting ◽  
Bark Thickness ◽  
Optimal Model ◽  
Breast Height ◽  
Starting Point ◽  
Mean Diameter ◽  
The Mean ◽  
Actual Method

Background and Purpose: Bark thickness and its share in the volume of roundwood are the most important characteristics of the bark, particularly in the process of timber harvesting, and during scaling of processed logs. Therefore it is very important to have at disposal relatively accurate data regarding these characteristics of bark for particular tree species. The main goal of this paper is to investigate the thickness of the bark and its share in the volume of roundwood of Norway spruce. Materials and Methods: The research was carried out in the area of the Canton 10 of the Federation of Bosnia and Herzegovina and it encompassed 393 trees of Norway spruce from 10 cm to 115 cm of thickness at breast height. Measuring of the mean diameter and double thickness of bark was conducted by section method. In total, 4,647 diameters and bark thicknesses were measured in different relative lengths of stems or in average 10.6 measurements per one stem. Results: As an optimal model for the evaluation of double thickness of the bark of Norway spruce depending on mean diameter of roundwood the function with designated determination coefficient of 0.7142 was selected. The obtained results have confirmed the previously defined relations of investigate characteristics, which are as following: a) with the increase of mean diameter of roundwood (section) double bark thickness is increased from 9.26 mm (thickness class 12.5 cm) to 31.65 mm (thickness class 92.5 cm); b) with the increase of mean diameter of roundwood the share of bark in its volume decreased from 14.26% (thickness class 12.5 cm) to 6.73% (thickness class 92.5 cm). Conclusions: By the actual method of estimating bark thickness or the share of bark in the volume of roundwood of Norway spruce in the forestry of the Federation of Bosnia and Herzegovina a significant error was created which increases with the increase of mean diameter. The obtained results point to the necessity of investigation of these bark characteristics in Bosnia and Herzegovina and represent an inevitable starting point for making adequate tables of bark thickness and its percentage share in the volume of roundwood of Norway spruce.

scholarly journals Productivity of black locust (Robinia pseudoacacia L.) stands on chernozem in Vojvodina

2014 ◽  
pp. 9-31
Author(s):  
Sinisa Andrasev ◽  
Savo Roncevic ◽  
Petar Ivanisevic ◽  
Sasa Pekec ◽  
Martin Bobinac
Keyword(s):  
Soil Type ◽  
Black Locust ◽  
Robinia Pseudoacacia ◽  
Diameter Growth ◽  
Sample Plot ◽  
Considerable Variability ◽  
Aeolian Sand ◽  
Breast Height ◽  
The Mean ◽  
Robinia Pseudoacacia L

This paper presents the elements of growth of black locust trees and stands in 15 sample plots in Vojvodina, at the age of 21-68 years. In each sample plot, based on soil profile horizons the determined soil type was chernozem as well as its lower systematic units (subtype, variety and form), according to the Skoric et al. (1985) classification. On the basis of the mean stand heights (hL), the stands on the subtype of chernozem on loess and loesslike sediments belong to height classes I-IV, and stands on calcareous aeolian sand to classes II-V (according to R e d e i et al. 2014), which indicates their considerable variability with respect to productivity within the determined subtypes of chernozem. Significant differences at the level of chernozem subtypes were found between the mean heights (p = 0.032), but not between the mean diameters (p = 0.083). The mean diameters at breast height in the studied black locust stands were on average lower than the models of diameter growth for the appropriate height classes and determined by a larger number of trees per hectare than in the tables (R e d e i et al, 2014). The volume per hectare is higher than in the tables also being conditioned by the large number of trees per hectare.

scholarly journals Sample Size to Estimate the Mean and Median of Traits in Canola

2018 ◽  
Vol 10 (11) ◽  
pp. 123
Author(s):  
Alberto Cargnelutti Filho ◽  
Cleiton Antonio Wartha ◽  
Jéssica Andiara Kleinpaul ◽  
Ismael Mario Marcio Neu ◽  
Daniela Lixinski Silveira
Keyword(s):  
Sample Size ◽  
Aerial Part ◽  
Dry Matter ◽  
Central Tendency ◽  
Sample Sizes ◽  
Brassica Napus L ◽  
Fresh Matter ◽  
The Mean ◽  
Productive Traits ◽  
Larger Sample

The aim of this study was to determine the sample size (i.e., number of plants) required to estimate the mean and median of canola (Brassica napus L.) traits of the Hyola 61, Hyola 76, and Hyola 433 hybrids with precision levels. At 124 days after sowing, 225 plants of each hybrid were randomly collected. In each plant, morphological (plant height) and productive traits (number of siliques, fresh matter of siliques, fresh matter of aerial part without siliques, fresh matter of aerial part, dry matter of siliques, dry matter of aerial part without siliques, and dry matter of aerial part) were measured. For each trait, measures of central tendency, variability, skewness, and kurtosis were calculated. Sample size was determined by resampling with replacement of 10,000 resamples. The sample size required for the estimation of measures of central tendency (mean and median) varies between traits and hybrids. Productive traits required larger sample sizes in relation to the morphological traits. Larger sample sizes are required for the hybrids Hyola 433, Hyola 61, and Hyola 76, in this sequence. In order to estimate the mean of canola traits of the Hyola 61, Hyola 76 e Hyola 433 hybrids with the amplitude of the confidence interval of 95% equal to 30% of the estimated mean, 208 plants are required. Whereas 661 plants are necessary to estimate the median with the same precision.

scholarly journals A Study on the X ¯ and S Control Charts with Unequal Sample Sizes

Mathematics ◽  
2020 ◽  
Vol 8 (5) ◽  
pp. 698
Author(s):  
Chanseok Park ◽  
Min Wang
Keyword(s):  
Sample Size ◽  
Control Charts ◽  
Weighted Average ◽  
Missing Observations ◽  
Population Parameters ◽  
Sample Sizes ◽  
Cost Constraints ◽  
The Mean ◽  
True Population ◽  
Average Sample

The control charts based on X ¯ and S are widely used to monitor the mean and variability of variables and can help quality engineers identify and investigate causes of the process variation. The usual requirement behind these control charts is that the sample sizes from the process are all equal, whereas this requirement may not be satisfied in practice due to missing observations, cost constraints, etc. To deal with this situation, several conventional methods were proposed. However, some methods based on weighted average approaches and an average sample size often result in degraded performance of the control charts because the adopted estimators are biased towards underestimating the true population parameters. These observations motivate us to investigate the existing methods with rigorous proofs and we provide a guideline to practitioners for the best selection to construct the X ¯ and S control charts when the sample sizes are not equal.

Post-stratified estimation: within-strata and total sample size recommendations

2011 ◽  
Vol 41 (5) ◽  
pp. 1130-1139 ◽  
Author(s):  
James A. Westfall ◽  
Paul L. Patterson ◽  
John W. Coulston
Keyword(s):  
Sample Size ◽  
Forest Inventory ◽  
Total Sample ◽  
Standard Errors ◽  
Sample Sizes ◽  
Total Sample Size ◽  
Survey Statistics ◽  
Population Structures ◽  
The Mean ◽  
Volume Estimates

Post-stratification is used to reduce the variance of estimates of the mean. Because the stratification is not fixed in advance, within-strata sample sizes can be quite small. The survey statistics literature provides some guidance on minimum within-strata sample sizes; however, the recommendations and justifications are inconsistent and apply broadly for many different population structures. The impacts of minimum within-strata and total sample sizes on estimates of means and standard errors were examined for two forest inventory variables: proportion forestland and cubic net volume. Estimates of the means seem unbiased across a range of minimum within-strata sample sizes. A ratio that described the decrease in variability with increasing sample size allowed for assessment of minimum within-strata sample requirements to obtain stable estimates of means. This metric indicated that the minimum within-strata sample size should be at least 10. Estimates of standard errors were found to be biased at small total sample sizes. To obtain a bias of less than 3%, the required minimum total sample size was 25 for proportion forestland and 75 for cubic net volume. The results presented allow analysts to determine within-stratum and total sample size requirements corresponding to their criteria for acceptable levels of bias and variability.

An evaluation of Merino wool quality:II. An estimate of the incidence of coarse fibres in Australian Merino wool

1970 ◽  
Vol 74 (1) ◽  
pp. 99-102 ◽  
Author(s):  
J. R. Gallagher
Keyword(s):  
Full Range ◽  
Fibre Diameter ◽  
Merino Wool ◽  
Coefficients Of Variation ◽  
Wide Range ◽  
Mean Diameter ◽  
The Mean ◽  
The Individual ◽  
Australian Merino

SUMMARYEstimates of the incidence of coarse fibres and medullation were made from 1014 bales of Merino greasy wool, from the five major wool-selling centres in Australia. A full range of wool types was represented from the fault-free spinners types to the burry, dusty, inferior topmakers' types. The wool consisted of 36 processors' lots ranging from 1 to 120 bales.The mean diameter of the 36 lots was 20·7 ± 5·3 μ 2·4% of the fibre population exceeded 30 μ the incidence of medullation was 1·1%.Mean diameters of the individual lots ranged from 14·7 to 25·3 μ Twenty-one of the 36 lots had coefficients of variation of mean fibre diameter which exceeded 23%. The range of clean, oven-dried yield was 49·4–69·1%. The between-lot variation in fibre medullation was 0–3·1%.It is concluded that fibre coarseness as measured by diameter was not a problem in the wide range of wool sampled. However, the incidence of medullation is an increase on previous estimates and should be a cause of concern to breeders.

scholarly journals Sampling of cashew nuts from cashew tree clones

2020 ◽  
Vol 42 (1) ◽  
Author(s):  
Adroaldo Guimarães Rossetti ◽  
Francisco das Chagas Vidal Neto ◽  
Levi de Moura Barros
Keyword(s):  
Sample Size ◽  
Genetic Improvement ◽  
Morphological Study ◽  
Stratified Sampling ◽  
Anacardium Occidentale ◽  
Sample Sizes ◽  
Margin Of Error ◽  
The Mean ◽  
Cashew Tree

Abstract The aim of this work was to estimate sample sizes to assist the genetic improvement of the cashew tree (Anacardium occidentale L.). Stratified sampling, comprising five strata (S5, S4, S3, S2, and S1) of five cashew clones (BRS 274, BRS 275, BRS 226, BRS 189 and CCP 76), was effective for estimating the different sample sizes of the nut. Sample size for each clone depends on the weight-nut variance, the margin of error B permitted in the estimates and the desired precision of the results. The increases in sample size with clone variance, lowered the permitted margin of error B, and increased the desired precision of the results. These clones required different sample sizes for a morphological study of the nuts. Larger nuts require larger samples for the same margin of error B. For an error B of 0.2g, the sample size for clones S5, S4 and S3 were n5 = 84, n4 = 49 and n3 = 37 nuts. For clones BRS 274 (S5) and BRS 275 (S4), with better nut classification, the mean weights were respectively 16.79 and 12.78g. Clones BRS 189 (S2) and CCP 76 (S1), with smaller nuts, have a smaller variances, s22 = 0.7638 and s12 = 1.0712, where the mean weight was 8.29 and 7.81g respectively.

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