scholarly journals Investigating possible changes of extreme annual rainfall in Zimbabwe

2008 ◽  
Vol 5 (4) ◽  
pp. 1765-1785 ◽  
Author(s):  
D. Mazvimavi
Keyword(s):  
Global Warming ◽  
Regression Analysis ◽  
Water Resources ◽  
Quantile Regression ◽  
Rainy Season ◽  
Kendall Test ◽  
Annual Rainfall ◽  
Management Approach ◽  
Average Rainfall ◽  
Quantile Regression Analysis

Abstract. There is increasing concern about the perceived decline in rainfall which is sometimes attributed to global warming. Some studies have concluded that average rainfall in Zimbabwe has declined by 10% or 100 mm/yr during the last 100 yrs. This paper investigates the validity of the assumption that rainfall is declining in Zimbabwe. Time series of annual rainfall, and total rainfall for a) the early party of the rainy season, October-November-December (OND), and b) the mid to end of the rainy season, January-February-March (JFM) are analysed for the presence of trends using the Mann-Kendall test, and changes in extreme rainfall using quantile regression analysis. The analysis has been done for 40 rainfall stations with records starting during the 1892–1940 period and ending in 2000, and representative of the major rainfall regions. The Mann-Kendal test did not identify a significant trend at all the 40 stations, and therefore there is no proof that the average rainfall at each of these stations has changed. Quantile regression analysis revealed a decline in annual rainfall less than the tenth percentile at only one station, and increasing rainfall for rainfall greater than the ninetieth percentile at another station. All the other stations revealed no changes over time in both the extreme low and high rainfall at the annual interval. Therefore, there is no evidence that the frequency and severity of droughts has changed during the 1892 to 2000 period. The general perception about declining rainfall is likely shaped by a comparison of the recent drought years (1980's–1990's) to recent wet periods (1970's). There have however been periods with similar dry years beyond the recallable memory, e.g. 1926–1936, 1940's. Crop failures and livestock losses attributed to declining rainfall are most likely due to poor agricultural practices such as production of crops in unsuitable climatic regions, degradation of rangelands partly due to increasing livestock populations. Rainfall in Zimbabwe has high inter-annual variability, and currently any change due to global warming is not yet statistically detectable. The annual renewal rate of water resources from rainfall has therefore not changed, and an adaptive water resources management approach is called to overcome problems arising from increasing water demand, and variability of available water resources.

scholarly journals Investigating changes over time of annual rainfall in Zimbabwe

2010 ◽  
Vol 14 (12) ◽  
pp. 2671-2679 ◽  
Author(s):  
D. Mazvimavi
Keyword(s):  
Time Series ◽  
Regression Analysis ◽  
Quantile Regression ◽  
Rainy Season ◽  
Annual Rainfall ◽  
Rainfall Time Series ◽  
Average Rainfall ◽  
Quantile Regression Analysis ◽  
Changes Over Time ◽  
Over Time

Abstract. There is increasing concern in southern Africa about the possible decline of rainfall as a result of global warming. Some studies concluded that average rainfall in Zimbabwe had declined by 10% or 100 mm during the last 100 years. This paper investigates the validity of the assumption that rainfall is declining in Zimbabwe. Time series of annual rainfall, and total rainfall for (a) the early part of the rainy season, October-November-December (OND), and (b) the mid to end of the rainy season, January-February-March (JFM) are analysed for the presence of trends using the Mann-Kendall test, and for the decline or increase during years with either high or low rainfall using quantile regression analysis. The Pettitt test has also been utilized to examine the possible existence of change or break-points in the rainfall time series. The analysis has been done for 40 rainfall stations with records starting during the 1892–1940 period and ending in 2000, and representative of all the rainfall regions. The Mann-Kendal test did not identify a significant trend at all the 40 stations, and therefore there is no proof that the average rainfall at each of these stations has changed. Quantile regression analysis revealed a decline in annual rainfall less than the tenth percentile at only one station, and increasing of rainfall greater than the ninetieth percentile at another station. All the other stations had no changes over time in both the low and high rainfall at the annual interval. Climate change effects are therefore not yet statistically significant within time series of total seasonal and annual rainfall in Zimbabwe. The general perception about declining rainfall is likely due to the presence of multidecadal variability characterized by bunching of years with above (e.g. 1951–1958, 1973–1980) and below (e.g. 1959–1972, 1982–1994 ) average rainfall.

scholarly journals Association between leukocyte telomere length and sex by quantile regression analysis

2021 ◽  
Author(s):  
Fernanda Gutierrez-Rodrigues ◽  
Raquel M. Alves-Paiva ◽  
Natália F. Scatena ◽  
Edson Z. Martinez ◽  
Priscila S. Scheucher ◽  
...  
Keyword(s):  
Regression Analysis ◽  
Quantile Regression ◽  
Telomere Length ◽  
Leukocyte Telomere Length ◽  
Quantile Regression Analysis

Determinants of liquidity in Malaysian SMEs: a quantile regression approach

2018 ◽  
Vol 67 (9) ◽  
pp. 1566-1584 ◽  
Author(s):  
Shaista Wasiuzzaman
Keyword(s):  
Regression Analysis ◽  
Quantile Regression ◽  
Emerging Market ◽  
Developed Countries ◽  
Data Availability ◽  
Firm Level ◽  
Liquidity Management ◽  
Ols Regression ◽  
Content Type ◽  
Quantile Regression Analysis

PurposeThe management of liquidity has always been seen as a critical but often ignored issue in finance. Despite the abundance of studies on liquidity management, these studies mainly focus on developed countries and on large firms. Liquidity is critical for the small firm but studies on liquidity management in small and medium enterprises (SMEs) are lacking. The purpose of this paper is to examine the firm-level determinants of liquidity of SMEs in Malaysia.Design/methodology/approachData are collected for a total of 986 small firms in Malaysia from 2011 to 2014, resulting in a total of 2,683 observations. Firm-specific variables and the effect of the economy are considered as the possible determinants of liquidity. Ordinary least squares (OLS) regression analysis with standard errors adjusted for firm-level clustering and quantile regression analysis are used for this purpose.FindingsAnalysis using OLS regression technique indicates that a firm’s profitability, its growth, asset tangibility, size, age and firm status are significant factors in influencing its liquidity decision. Leverage and economic condition are not found to have any significant influence on liquidity. However, quantile regression analysis provides a different picture especially for SMEs with liquidity at the quantile levels ofθ=0.10 and 0.90. Atθ=0.10, only profitability, tangibility and firm status are significant, while atθ=0.90, tangibility, size, firm status and, to some extent, age are significant in influencing liquidity levels.Originality/valueTo the author’s knowledge, this is the first study analyzing the liquidity decision of SMEs in an emerging market such as Malaysia. Most studies on liquidity management of SMEs are focused on developed countries due to data availability but these studies are also only a handful. Additionally, this study uses quantile regression analysis which highlights the need to analyze financial decisions at different levels rather than at the aggregate level as done in OLS regression analysis.

Absenteeism and performance in a quantitative module A quantile regression analysis

2016 ◽  
Vol 8 (3) ◽  
pp. 376-389 ◽  
Author(s):  
Pranab Kumar Pani ◽  
Pallavi Kishore
Keyword(s):  
Regression Analysis ◽  
Academic Performance ◽  
Learning Styles ◽  
Quantile Regression ◽  
United Arab Emirates ◽  
Classroom Environment ◽  
Negative Impact ◽  
Content Type ◽  
Quantile Regression Analysis ◽  
And Performance

Purpose – There is growing evidence that learning is faster, measurably better and more productive in a classroom setting when a student attends classes regularly. Each student brings in his/her experience, skills, and unique learning styles to a class – thus a classroom environment can potentially create positive externalities through which a student can gain substantially from various strengths of his/her peers. However, students do remain absent from their classes for a variety of reasons. One of the measurable effects of regular non-attendance in a university class, where students from various cultures and regions interact, is the academic performance. The purpose of this paper is to determine if there is any potential causal link between absenteeism (attendance) and academic performance. Design/methodology/approach – Data were culled from the records of three batches of students in a British university campus in the Middle East. Quantile regression methods were used to establish the causal relationship between absenteeism and academic performance. Findings – A quantile regression analysis reveals that absenteeism has negative impact on academic performance. This also suggests that low performers are worse affected by absenteeism as compared to the high performers. Research limitations/implications – Inclusion of some other factors, such as study habits, additional hours spent on quantitative modules, student’s ethnicity background, particularly in the context of United Arab Emirates, could have emboldened the robustness of the study. Non-availability or paucity of this information, to some degree, has limited the conclusions of this study. Originality/value – Proponents of mandatory attendance argue that there is a positive correlation between attendance and performance. But, one very important issue which gets overlooked is who actually benefits more by attending classes – are the shirkers who have a poor attendance record or the ones who are more sincere, more regular, and active participants in a class? This study uses quantile regression analysis to address this issue.

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