Physical Sciences and Mathematics Commons^™

The Power Of Structured Designs And Mixed Models In A Real World Experiment, J. C. Galland, G. A. Milliken, D. R. Hyatt, M. Hornback, K. Cudjoe

Conference on Applied Statistics in Agriculture

Justifications usually given for adopting an automated system pertain to a reduction in labor and an improvement in quality control. A manufacturer of a prototype instrument that automated some of the steps for culturing bacteria wanted to compare the automated system to the manual system. The manufacturer wanted to compare the two systems in 1) Total time needed to isolate the target bacteria, 2) Ability to isolate the target bacteria, 3) Amount of interference from background (non-target) bacterial growth, and 1) Extent of cross (sample to sample) contamination.

This paper presents the experimental design used to make these comparisons and …

Investigating Power Of Analysis Of Covariance Methods, James R. Schwenke, J. Mark Donovan

Conference on Applied Statistics in Agriculture

Analysis of covariance is a well-utilized statistical methodology. The procedure involves a series of statistical tests to first construct a most significant analysis model to characterize the effect of the covariate on response. Pairwise comparisons among treatments are then based on the finalized model.

For traditional Normal error assumptions, each step of the process is based on exact statistical tests. However, the series of statistical tests defines a conditional probability scheme with possible multiplicity issues. The question then becomes if the analysis of covariance methodology considered in entirety is able to maintain a nominal level of significance with good power. …

Starting Values For Proc Mixed With Repeated Measures Data, J. C. Recknor, W. W. Stroup

Conference on Applied Statistics in Agriculture

A major advantage of PROC MIXED for repeated measures data is that one could choose from many different correlated error models. However, MIXED uses default starting values that may cause difficulty obtaining REML estimates of the covariance parameters for several of the models available. This can take the form of excessively long run times or even failure to converge. We have written a program to obtain initial covariance parameter estimates that result in greatly improved performance of the REML algorithm. We will use two covariance models frequently of interest in animal health experiments, the first-order ante-dependence model [ANTE(l)] and the …

Analysis Of Genotype-By-Environment Interaction With Ammi Models Using Sas Proc Mixed, Raul E. Macchiavelli, James S. Beaver

Conference on Applied Statistics in Agriculture

Genotype-by-environment (GE) interaction can be analyzed using different approaches. Among these, the additive main effects and multiplicative interaction model yields useful interpretations and can be applied successfully to plant breeding programs. In this paper we review fitting strategies for this model and show how to combine the capabilities of the Mixed and IML procedures in SAS to fit this model. This permits straightforward use of likelihood-based inference in standard and non standard situations like complex experimental designs. The proposed procedures were applied to data from red mottled bean variety trials conducted in the Dominican Republic and Puerto Rico in 9 …

The Analysis Of Count Data In A One-Way Layout, Yuhua Wang, Dallas E. Johnson, Linda J . Young

Conference on Applied Statistics in Agriculture

An efficient score statistic for testing the equality of the means of several groups of count data in the presence of a common dispersion parameter is introduced and a new approximation to its distribution is given. The performance of the efficient score statistic using this approximation, the original efficient score statistic approximated by X ² (t -1), the likelihood ratio statistic and four more ANOVA methods based on raw data or transformed data are compared in terms of size and power by using Monte Carlo simulations. The efficient score statistic with its new approximation is recommended. An application is given.

Hydrological Normalization Of Nutrient Deliveries From Agricultural Catchments, Per Stalnacke, Anders Grimvall

Conference on Applied Statistics in Agriculture

Nutrient deliveries from agricultural catchments are strongly influenced by natural fluctuations in water discharge. Hydrological normalization of such data may therefore facilitate estimation of human impact on the environment. In the present study, we compared conventional statistical normalization techniques with a recently proposed, semi-parametric regression technique, which can accommodate time-dependent relationships between nutrient deliveries and water discharge. Case studies of agricultural catchments in Sweden and Norway demonstrated that all of the tested normalization techniques were able to remove a substantial fraction of the interannual variation in nitrogen deliveries, whereas normalization of phosphorus loads was problematic. Semi-parametric regression models were found …

A Computationally Efficient Method For Determining Significance In Interval Mapping Of Quantitative Trait Loci, Dan Nettleton

Conference on Applied Statistics in Agriculture

This paper provides a brief introduction to the mapping of quantitative trait loci (QTL). An example on mapping QTL for root thickness in rice is presented to illustrate popular statistical methods used in QTL mapping. Interval mapping is used in conjunction with permutation testing techniques to detect significant associations between genetic positions and quantitative traits while controlling overall type I error rate. A review of a recent technique that can greatly reduce the computational expense of permutation testing in QTL mapping is discussed. Theory is provided for an extension of recent results that may lead to more powerful methods of …

An Improved Estimator For Assessing The Measure Of Agreement With A Gold Standard, Brent D. Burch, Ian R. Harris, Roy T. St. Laurent

Conference on Applied Statistics in Agriculture

St. Laurent (1998, Biometrics 54, 537-545) developed a measure of agreement for method comparison studies in which an approximate method of measurement is compared to a gold standard method of measurement. The measure of agreement proposed was shown to be related to a population intraclass correlation coefficient. This paper develops a family of estimators for the measure of agreement based on pivotal quantities. A blend of two particular members of the family is suggested as an estimator itself. In general, this estimator outperforms the maximum likelihood estimator in terms of bias and mean-squared error.

Nonlinear Models For Multi-Factor Plant Nutrition Experiments, R. D. Landes, W. W. Stroup, E. T. Paparozzi, M. E. Conley

Conference on Applied Statistics in Agriculture

Plant scientists are interested in measuring plant response to quantitative treatment factors, e.g. amount of nutrient applied. Response surface methods are often used for experiments with multiple quantitative factors. However, in many plant nutrition studies, second-order response surface models result in unacceptable lack of fit. This paper explores multi-factor nonlinear models as an alternative. We have developed multi-factor extensions of Mitscherlich and Gompertz models, and fit them to data from experiments conducted at the University of Nebraska-Lincoln Horticulture department. These data are typical of experiments for which conventional response surface models perform poorly. We propose design selection strategies to facilitate …

Using Isotonic Regression To Improve Estimation In Factorial Experiments With Ordered Factor Levels, Matt Strand, Jim Higgins

Conference on Applied Statistics in Agriculture

In many designed experiments in agriculture and the life sciences, a researcher can anticipate the direction that responses will take when treatments are varied. For example, in a 2-way factorial, a researcher may know that increasing the levels of nitrogen and phosphorus will increase yields of a crop. Classical analysis of variance does not take into account a known ordering among population means. However, it can be shown that by restricting the estimates of means to have the same ordering as the anticipated ordering of population means, a reduction in mean-squared errors of estimators will likely occur, often by more …

Characterizing The Statistical Distribution Of Organic Carbon And Extractable Phosphorus At A Regional Scale, John J. Brejda, David W. Meek, Douglas L. Karlen

Conference on Applied Statistics in Agriculture

Greater awareness of potential environmental problems has created the need to monitor total organic carbon (TOC) and extractable phosphorus (P) concentrations at a regional scale. The probability distribution of these soil properties can have a significant effect on the power of statistical tests and the quality of inferences applied to these properties. The objectives of this study were to: (1) evaluate the probability distribution of TOC and extractable P at the regional scale in three Major Land Resource Areas (MLRA), and (2) identify appropriate transformations that will result in a normal distribution. Both TOC and extractable P were non-normally distributed …

Analysis Of Nuclei Fluorescence Histograms Using Non-Linear Functions Or Wavelets, Susanne Aref, Maria Kocherginsky, Carrie A. Northcott, Lane A. Rayburn

Conference on Applied Statistics in Agriculture

Histograms based on 5,000 nuclei from cells (Chinese hamster ovary cells, bone marrow cells) are used to determine the coefficient of variation (CV) of observations surrounding the highest peak. The cells are subjected to various treatments, for example exposure to herbicides. By eyeballing the histogram, an interval under the highest peak is determined. The CV calculated from the histogram on the eyeballed interval is the response variable in an ANOVA. To avoid the subjectivity of eyeballing the histogram, non-linear functions such as the Gaussian density function can be used to model the histogram. The CV may then be determined from …

On Using Proc Mixed For Longitudinal Data, Walter W. Stroup

Conference on Applied Statistics in Agriculture

PROC MIXED has become a standard tool for analyzing repeated measures data. Its popularity results from a wide choice of correlated error models compared to other software, e.g. PROC GLM. However, PROC MIXED's versatility comes at a price. Users must take care. Problems may result from MIXED defaults. These include: questionable criteria for selecting correlated error models; starting values that may impede REML estimation of covariance components; and biased standard errors and test statistics. Problems may be induced by inadequate design. This paper is a survey of current knowledge about mixed model methods for repeated measures. Examples are presented using …

Modeling The Fate Of Toxic Chemicals In Soils, Anabayan Kessavalou, Anne M. Parkhurst

Conference on Applied Statistics in Agriculture

Studies on the fate of toxic chemicals in soils are often reported with a minimum of descriptive statistics. Use of modeling techniques to describe the kinetics of chemical degradation provides a better understanding of the fate of chemicals in soil systems. When modeling nonlinear systems, assumptions made about the error term greatly influence the parameter estimation. Inappropriate use of linearization and failure to account for autocorrelated errors may result in inaccurate models. Information is also needed about the effects of the magnitude of autocorrelation on parameter estimation. The exponential decay function was chosen to fit the data obtained from a …

Estimating The Likelihood Of Yellow Starthistle Occurrence Using An Empirically Derived Nonlinear Regression Model, Bahman Shafii, William J. Price, Lawrence W. Lass, Donn C. Thill

Conference on Applied Statistics in Agriculture

Yellow starthistle is a noxious weed common in the semiarid climate of Central Idaho and other western states. Early detection of yellow starthistle and predicting its infestation potential have important scientific and managerial implications. Weed detection and delineation are often carried out by visual observation or survey techniques. However, such methods may be ineffective in detecting sparse infestations. The distribution of yellow starthistle over a large region may be affected by various exogenous variables such as elevation, slope and aspect. These landscape variables can be used to develop prediction models to estimate the potential invasion of yellow starthistle into new …

Statistics In The New Millennium: Some Personal Views, Bryan F.J. Manly

Conference on Applied Statistics in Agriculture

In this paper I discuss three topics that I believe are relevant to the subject of statistics in the new millennium: (a) the impact of computers, and the state of computer-intensive methods as far as practical applications of statistics are concerned; (b) methods for the analysis of the extremely large data sets that are now becoming available; and (c) the use of statistics by scientists in general. For the first topic I suggest that the main advantage of computer-intensive methods is that they can under certain circumstances give simple and believable answers to questions when other methods fail. However, I …

Editor's Preface And Table Of Contents, George A. Milliken

Conference on Applied Statistics in Agriculture

These proceedings contain papers presented in the eleventh annual Kansas State University Conference on Applied Statistics in Agriculture, held in Manhattan, Kansas, April 25-27, 1999.

Marketing Alfalfa Hay: What The Consumer Demands, Tom Keene

Kentucky Alfalfa and Stored Forage Conference

Anytime we address selling a product to the consumer; our first objective should always be to sell a quality product. However before we get into quality, I think we need to back up and understand that quality can vary from customer to customer depending upon the type of livestock he is feeding. For instance, if you are selling hay to a dairy operation, how is the hay being utilized? Is it being fed free choice? Is it going into a milking TMR (total mixed ration)? Is it going to feed young stock, breeding heifers, or sick animals? Each group of …

How I Produce And Market Alfalfa Hay, John Nowak

Kentucky Alfalfa and Stored Forage Conference

John Nowak was born March 22, 1947, in New York City and was raised in Westchester County, just north of New York City. After graduating from Colorado State University with a B.S. degree in farm and ranch management, he entered the U.S. Army. John served on active duty from 1969 until 1978. In 1975, his Army career brought him to Fort Campbell, Kentucky, and he began farming part-time in Christian County in 1976. As with many "start-from-scratch" farmers, John's first farming efforts involved producing burley tobacco during the years 1976 through 1979. In 1979, he began a cow-calf and backgrounding …

Grazing Alfalfa, Garry D. Lacefield, Jimmy C. Henning

Kentucky Alfalfa and Stored Forage Conference

Alfalfa is a high yielding, high quality, deep-rooted, versatile forage legume well adapted throughout the U.S. Gains per animal and per acre can be excellent with acceptable stand persistence when present technology is used. Is grazing alfalfa right for everyone? No. Is grazing alfalfa right for you? Only you can answer that question. This presentation attempts to give you information that will hopefully help you with that answer.

What I Have Learned From 4 Years Of Alfalfa Grazing Tolerance Variety Trials, Jimmy C. Henning, Robert Spitaleri, Garry D. Lacefield, Charles T. Dougherty

Kentucky Alfalfa and Stored Forage Conference

There has been interest in alfalfa varieties that would tolerate grazing for some time. The spreading type alfalfas (such as Rambler, Spredor 2, Travois) have long been generally promoted as being tolerant of grazing. Over the years, most selection for tolerance to grazing was done using frequent clipping to simulate grazing.

Studies conducted at the University of Georgia in the 1980's found that alfalfa varieties performed differently when grazed frequently compared to clipping frequently. This line of research eventually led to the release of 'AlfaGraze' alfalfa which was the first variety ever to be selected primarily by overgrazing by livestock. …

Practical And Economical Ways To Increase Alfalfa Hay Drying Rates, Michael Collins

Kentucky Alfalfa and Stored Forage Conference

Hay stores well for long periods and is better suited to cash sale and transportation than silage and remains the most popular method for harvesting the alfalfa crop. Rapid drying reduces field losses by reducing respiration and by reducing the incidence of rain damage during curing. Because of these factors, harvest losses are greatest for very dry forage and are low for very wet material like direct cut silage. However, the latter is subject to excessive storage losses due to seepage and to quality deterioration. Storage losses are generally minimized by harvesting at low moisture levels.

Alfalfa Following Alfalfa: What Works And What Doesn't Work?, Monroe Rasnake

Kentucky Alfalfa and Stored Forage Conference

Farmers often would like to go directly back into alfalfa when an old stand plays out. However, research has shown that it is often difficult to get new stands established when this is done. Some of the problems may be attributed to weeds, insects and diseases that build up over time and become difficult to control. Another reason is that alfalfa plants have been shown to produce chemical compounds that can inhibit germination and growth of new seedlings. This effect is called allelopathy or autotoxicity.

Secrets To Getting A Good Stand Of Alfalfa, Jimmy C. Henning, Garry D. Lacefield

Kentucky Alfalfa and Stored Forage Conference

Getting a good stand of alfalfa quickly is very important to Kentucky because it is the highest yielding, highest quality forage crop. In addition, it can be used in many different ways. Cool wet springs and hot dry falls have caused alfalfa seedings to fail in recent years. It would be easy to begin to believe that there was some 'magic' step or ingredient that has been missing. There are no magic steps to getting a good stand. Attention to a few major details can help maximize your chances of success.

What Grasses Work Best With Alfalfa?, Timothy D. Phillips

Kentucky Alfalfa and Stored Forage Conference

Alfalfa is the "queen" of forages, but many situations exist where it is desirable or necessary to grow alfalfa in a mixture with a forage grass rather in monoculture. Some of the reasons to grow grass with alfalfa are: improved yield (in terms of tons of dry matter produced), better seasonal yield distribution, better weed control, potential pest reduction, erosion prevention, bloat risk reduction, and accelerated hay-drying rates. Conversely, there are some factors that favor alfalfa monoculture. These include: lower forage quality, especially in terms of protein content; more difficult management requirements (herbicide use, fertilization, and harvest timing); and, lower …

Foreword [1999], Garry D. Lacefield

Kentucky Alfalfa and Stored Forage Conference

This is the front matter of the proceedings.