Analysis and comparison of nonlinear tree height prediction strategies for Douglas-fir forests

2008 ◽  
Vol 38 (3) ◽  
pp. 553-565 ◽  
Author(s):  
H. Temesgen ◽  
V. J. Monleon ◽  
D. W. Hann
Keyword(s):  
Relative Position ◽  
Fixed Effects ◽  
Stand Density ◽  
Tree Height ◽  
Predictive Performance ◽  
Douglas Fir ◽  
Fixed Effects Model ◽  
Nonlinear Mixed Effects Models ◽  
Data Set ◽  
Height Prediction

Using an extensive Douglas-fir data set from southwest Oregon, we examined the (1) performance and suitability of selected prediction strategies, (2) contribution of relative position and stand-density measures in improving tree height (h) prediction values, and (3) effect of different subsampling designs to fill in missing h values in a new stand using a regional nonlinear model. Nonlinear mixed-effects models (NMEM) substantially improved the accuracy and precision of height prediction over the conventional nonlinear fixed-effects model (NFEM) that assumes the observations are independent, particularly when a few trees are subsampled for height. The predictive performance of a correction factor on a NFEM with relative position and stand-density measures was comparable to that of a NMEM when four or more trees were subsampled for height. When two or more heights were randomly subsampled, the NMEM efficiently explained the differences in the height–diameter relationship because of the variations in relative position of trees and stand density without having to incorporate them into the model. When only one height was subsampled, selecting the largest diameter tree in the stand would result in a lower predicted root mean square error (RMSE) than randomly selecting the height, regardless of the model form or fitting strategy used.

A big data approach to examining social bots on Twitter

2019 ◽  
Vol 33 (4) ◽  
pp. 369-379 ◽  
Author(s):  
Xia Liu
Keyword(s):  
Big Data ◽  
Fixed Effects ◽  
Latent Dirichlet Allocation ◽  
User Generated Content ◽  
Fixed Effects Model ◽  
Data Set ◽  
Information Distortion ◽  
Content Type ◽  
Related Information ◽  
Brand Reputation

Purpose Social bots are prevalent on social media. Malicious bots can severely distort the true voices of customers. This paper aims to examine social bots in the context of big data of user-generated content. In particular, the author investigates the scope of information distortion for 24 brands across seven industries. Furthermore, the author studies the mechanisms that make social bots viral. Last, approaches to detecting and preventing malicious bots are recommended. Design/methodology/approach A Twitter data set of 29 million tweets was collected. Latent Dirichlet allocation and word cloud were used to visualize unstructured big data of textual content. Sentiment analysis was used to automatically classify 29 million tweets. A fixed-effects model was run on the final panel data. Findings The findings demonstrate that social bots significantly distort brand-related information across all industries and among all brands under study. Moreover, Twitter social bots are significantly more effective at spreading word of mouth. In addition, social bots use volumes and emotions as major effective mechanisms to influence and manipulate the spread of information about brands. Finally, the bot detection approaches are effective at identifying bots. Research limitations/implications As brand companies use social networks to monitor brand reputation and engage customers, it is critical for them to distinguish true consumer opinions from fake ones which are artificially created by social bots. Originality/value This is the first big data examination of social bots in the context of brand-related user-generated content.

scholarly journals The Negative Effect of Smartphone Use on Academic Performance May Be Overestimated: Evidence From a 2-Year Panel Study

2020 ◽  
Vol 31 (11) ◽  
pp. 1351-1362
Author(s):  
Andreas Bjerre-Nielsen ◽  
Asger Andersen ◽  
Kelton Minor ◽  
David Dreyer Lassen
Keyword(s):  
Academic Performance ◽  
Fixed Effects ◽  
Panel Study ◽  
Student Characteristics ◽  
Fixed Effects Model ◽  
Data Set ◽  
Course Characteristics ◽  
Negative Effect ◽  
Smartphone Use ◽  
The Relationship

In this study, we monitored 470 university students’ smartphone usage continuously over 2 years to assess the relationship between in-class smartphone use and academic performance. We used a novel data set in which smartphone use and grades were recorded across multiple courses, allowing us to examine this relationship at the student level and the student-in-course level. In accordance with the existing literature, our results showed that students’ in-class smartphone use was negatively associated with their grades, even when we controlled for a broad range of observed student characteristics. However, the magnitude of the association decreased substantially in a fixed-effects model, which leveraged the panel structure of the data to control for all stable student and course characteristics, including those not observed by researchers. This suggests that the size of the effect of smartphone usage on academic performance has been overestimated in studies that controlled for only observed student characteristics.

scholarly journals Regional Height–Diameter Equations for Major Tree Species of Southwest Oregon

2007 ◽  
Vol 22 (3) ◽  
pp. 213-219 ◽  
Author(s):  
Hailemariam Temesgen ◽  
David W. Hann ◽  
Vincente J. Monleon
Keyword(s):  
Relative Position ◽  
Tree Species ◽  
Basal Area ◽  
Stand Density ◽  
Tree Height ◽  
Individual Tree ◽  
Fit Statistics ◽  
Alternative Measures ◽  
Southwest Oregon ◽  
Accuracy Of Prediction

Abstract Selected tree height and diameter functions were evaluated for their predictive abilities for major tree species of southwest Oregon. Two sets of equations were evaluated. The first set included four base equations for estimating height as a function of individual tree diameter, and the remaining 16 equations enhanced the four base equations with alternative measures of stand density and relative position. The inclusion of the crown competition factor in larger trees (CCFL) and basal area (BA), which simultaneously indicates the relative position of a tree and stand density, into the base height–diameter equations increased the accuracy of prediction for all species. On the average, root mean square error values were reduced by 45 cm (15% improvement). On the basis of the residual plots and fit statistics, two equations are recommended for estimating tree heights for major tree species in southwest Oregon. The equation coefficients are documented for future use.

Trend surface analysis of a Douglas-fir provenance–progeny transfer test

1988 ◽  
Vol 18 (5) ◽  
pp. 515-520 ◽  
Author(s):  
A. J. Thomson ◽  
Y. A. El-Kassaby
Keyword(s):  
Surface Analysis ◽  
Transfer Test ◽  
Block Design ◽  
Tree Height ◽  
Douglas Fir ◽  
Average Height ◽  
Trend Surface Analysis ◽  
Test Installation ◽  
Data Set ◽  
Trend Surface

Spatial variability in heights of 8-year-old Douglas-fir in a IUFRO provenance–progeny transfer test was analyzed using trend surface analysis to differentiate genetic and environmental effects on tree height. The test installation was located in the University of British Columbia Research Forest, and was a randomized incomplete block design with three replications. Only the 25 provenances that were replicated in each block and had a balanced data set (eight families, five trees per family) were used. Trends were fitted to the average height of each replicate of each provenance, and also to the average size of the largest and smallest families per replicate. Interpretation was based on the assumption that the effects of microsite (mainly grass invasion of one block) were defined by the trend surface, while genetic effects were represented by the residuals from the trend. The data had previously been analyzed by ANOVA methods and these results were contrasted with the results using trend surface analysis. Trend surface analysis generally gave results similar to ANOVA, but in some cases resulted in different conclusions. Additional insights into the interaction of genotype and environment were obtained. Trend surface analysis is proposed as a useful supplement to analysis of variance in provenance transfer studies. Potential problems in using the method are discussed.

scholarly journals COMPOSITION OF THE JOB-SEEKER STOCK IN LABOUR MARKET MATCHING :A STOCHASTIC FRONTIER APPROACH

2016 ◽  
Vol 3 (1) ◽  
pp. 63
Author(s):  
Sanna Mari Hynninen
Keyword(s):  
Labour Market ◽  
Technical Efficiency ◽  
Fixed Effects ◽  
Labour Force ◽  
Stochastic Frontier ◽  
Matching Function ◽  
Fixed Effects Model ◽  
Job Seekers ◽  
Data Set ◽  
Local Labour

This paper investigates the technical efficiency of labour market matching taking a stochastic frontierapproach. The data set consists of monthly data from 145 Local Labour Offices (LLOs) in Finland over theperiod 1995/01-2004/09. The true fixed-effects model is utilised in order to separate cross-sectionalheterogeneity from inefficiency. According to the results, there are notable differences in matching efficiencybetween regions, and these differences contribute significantly to the number of filled vacancies. If all regionswere as efficient as the most efficient one, the number of total matches per month would increase by over 10%. If inefficiency had no role in the matching function, the number of matches would increase by almost 24 %.The weight of the composition of the job-seeker stock and other environmental variables in the determinationof matching inefficiency is on average 61 %. In particular, job seekers out of the labour force and highlyeducated job seekers improve technical efficiency in the matching function

scholarly journals Media and Economic Growth: Country Groups Difference via Panel Data

2020 ◽  
Vol 5 (5) ◽  
Author(s):  
Viktoriia Ahapova
Keyword(s):  
Economic Growth ◽  
Panel Data ◽  
Fixed Effects ◽  
Panel Data Analysis ◽  
Press Freedom ◽  
Foreign Direct Investments ◽  
Fixed Effects Model ◽  
Data Set ◽  
The Press ◽  
Per Capita

The present article investigates the link between economic growth, namely GDP per capita, and the media activity represented with the indicator of the press freedom alongside other factors such as infrastructure, institutional conditions, and foreign direct investments. A panel of 179 countries was used for the period from 2000 to 2015. In particular, we run two panel data analysis models, fixed effects and random effects models, and examined their output with Hausman’s specification test, which pointed the fixed effects model as more efficient for the presented data set. However due to the presence of serial correlation, heteroskedastic, and cross-panel dependence, a Prais-Winsten regression with panel corrected standard errors (PCSE) was implemented. The comparative analysis of models of four country groups, divided by GNI per capita, was conducted. Both statistically significant correlation coefficients and models’ output provided evidence of an association between economic growth and the press activity.

scholarly journals Governance and Domestic Investment in Africa

2019 ◽  
Vol 8 (1) ◽  
pp. 63-80 ◽  
Author(s):  
Chimere Okechukwu Iheonu
Keyword(s):  
Fixed Effects ◽  
Principal Component ◽  
Domestic Investment ◽  
Fixed Effects Model ◽  
African Countries ◽  
Cross Sectional ◽  
Data Set ◽  
Governance Indicators ◽  
World Governance Indicators ◽  
The Impact

The study empirically examined the impact of governance on domestic investment in 16 African countries with a balanced panel data set, between the years 2002 and 2015. The study employed six unbundled governance indicators from the World Bank, World Governance Indicators and constructed three bundled governance indicators using the Principal Component Analysis. The Driscoll and Kraay Fixed Effects model which accounts for serial correlation, groupwise heteroskedasticity and cross-sectional dependence were employed with empirical results revealing that all the indicators of governance positively and significantly influence domestic investment in Africa, except for government effectiveness which happens to be insignificant. Also, Voice/Accountability and the Control of Corruption exert more influence on domestic investment as indicated by their coefficient values. Furthermore, economic growth is also an important factor in explaining domestic investment in Africa. Policy recommendations are discussed.

scholarly journals Do White Police Officers Unfairly Target Black Suspects?

2022 ◽  
Vol 4 (2) ◽  
pp. p12
Author(s):  
John R. Lott, Jr ◽  
Carlisle E. Moody
Keyword(s):  
Panel Data ◽  
Police Officers ◽  
Fixed Effects ◽  
The United States ◽  
Fixed Effects Model ◽  
Discrimination Test ◽  
Data Set ◽  
Unique Data ◽  
Fbi Data ◽  
The City

Using a unique data set we link the race of police officers who kill suspects with the race of those who are killed across the United States. We have data on a total of 2,706 fatal police killings for the years 2013 to 2015. This is 1,333 more killings by police than is provided by the FBI data on justifiable police homicides. We conducted three tests of discrimination. The results of these tests are different. In the first test we find some evidence that white officers are more likely to kill a black suspect who is later found to be unarmed than they are to kill an unarmed white suspect. However, this result could not be confirmed using a fixed effects model on panel data aggregated to the city level. In the second test, we find that white police officers are no more likely to kill an unarmed black suspect than are black or Hispanic officers. The results of this test are confirmed by the panel data version of the test. The third discrimination test indicated that black suspects, whether armed or not, are no more likely to be killed by a white officer than they are to be killed by black or Hispanic officers. Similarly, Hispanic suspects are no more likely to be killed by white offices than officers of other races. These results are also confirmed by panel data analyses. We find that when there is more than one officer on the scene, unarmed black suspects are not more likely to be killed by white police officers than unarmed white suspects. This could be evidence supporting a policy of reducing the number of officers working alone. Also, we find no evidence that body cameras affect either the number of police killings or the racial composition of those killings.

scholarly journals Effect of Rotation Age and Thinning Regime on Visual and Structural Lumber Grades of Douglas-Fir Logs

Forests ◽  
2018 ◽  
Vol 9 (9) ◽  
pp. 576
Author(s):  
Eini Lowell ◽  
Eric Turnblom ◽  
Jeff Comnick ◽  
CL Huang
Keyword(s):  
Stand Density ◽  
Tree Height ◽  
Douglas Fir ◽  
Timber Species ◽  
Market Demand ◽  
Rotation Age ◽  
The Impact ◽  
Grade Yield ◽  
Structural Lumber ◽  
Lumber Grade

Douglas-fir, the most important timber species in the Pacific Northwest, US (PNW), has high stiffness and strength. Growing it in plantations on short rotations since the 1980s has led to concerns about the impact of juvenile/mature wood proportion on wood properties. Lumber recovered from four sites in a thinning trial in the PNW was analyzed for relationships between thinning regime and lumber grade yield. Linear mixed-effects models were developed for understanding how rotation age and thinning affect the lumber grade yield. Log small-end diameter was overall the most important for describing the presence of an appearance grade, generally exhibiting an indirect relationship with the lower quality grades. Stand Quadratic Mean Diameter (QMD) was found to be the next most uniformly important predictor, its influence (positive or negative) depending on the lumber grade. For quantity within a grade, as log small-end diameter increased, the quantity of the highest grade increased, while decreasing the quantity of the lower grades differentially. Other tree and stand attributes were of varying importance among grades, including stand density, tree height, and stand slope, but logically depicted the tradeoffs or rebalancing among the grades as the tree and stand characteristics change. Structural lumber grade presence was described best by acoustic wave flight time, log position (decreasing presence in upper logs), and an increasing presence with rotation age. A smaller set of variables proved useful for describing quantity within a structural grade. Forest managers can use these results in planning to best capture value in harvesting, allowing them to direct raw materials (logs) to appropriate manufacturing facilities given market demand.

Abstract MP37: Macroeconomic Growth is Associated with Increases in Cardiovascular Mortality in Countries with Lower Social Protection Spending

Circulation ◽  
2015 ◽  
Vol 131 (suppl_1) ◽  
Author(s):  
Usama Bilal ◽  
Manuel Franco ◽  
Thomas A Glass
Keyword(s):  
Economic Growth ◽  
Cardiovascular Mortality ◽  
Fixed Effects ◽  
Social Protection ◽  
Welfare States ◽  
Time Varying ◽  
Fixed Effects Model ◽  
Data Set ◽  
Macroeconomic Growth ◽  
Cvd Mortality

Background: Macroeconomic growth has been shown to be associated with increases in cardiovascular (CVD) mortality. However, it is unclear whether concurrent social protection policies may mitigate the observed associations. Objective: To study if social protection expenditure modifies the association between macroeconomic growth and cardiovascular mortality. Methods: We included 21 OECD countries from 1980 to 2010 with available data in the Comparative Welfare States Data Set and the WHO Mortality Database. Gross Domestic Product (GDP) was used as a proxy for economic growth. Age-adjusted cardiovascular mortality rates were calculated. Countries were divided into tertiles of average Social Protection expenditure. We used fixed-effect models to study the association of GDP growth with CVD mortality stratified by tertile of social protection expenditure. We included four lagged GDP terms to account for the cyclical nature of GDP. A second fixed-effects model was fitted with time-varying linear and quadratic social protection expenditure and its interaction with GDP. Results: Overall, a 1% increase in GDP was associated with an increase in CVD mortality of 0.5% (95% CI: 0.21-0.83%, p=0.001). In countries with high and medium social protection expenditure, GDP increases were not associated with changes in CVD mortality (p=0.80 and p=0.52 respectively). In countries with the lowest social protection expenditure, a 1% GDP increase was associated with a significant increase in CVD mortality of 0.7% (95% CI: 0.04-1.32% p=0.03). These results were consistent in analysis using time-varying social protection expenditure (Figure). Conclusion: Our results highlight the need for social protection policies to accompany economic growth to mitigate its potential deleterious effects on cardiovascular diseases. Further research should study specific policies that mitigate the harmful effects of macroeconomic growth.

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