Principles and Procedures of Statistics
About: This article is published in Agronomy Journal.The article was published on 1961-09-01. It has received 5583 citations till now.
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TL;DR: The effects of violation of the assumptions underlying the fixed-effects analyses of variance (ANOVA) and covariance (ANCOVA) on Type-I and Type-II error rates have been of great concern to researchers and statisticians.
Abstract: The effects of violating the assumptions underlying the fixed-effects analyses of variance (ANOVA) and covariance (ANCOVA) on Type-I and Type-II error rates have been of great concern to researchers and statisticians. The major effects of violation of assumptions are now well known, after nearly four decades of research. Early summaries and reviews by Hey (1938), Garret and Zubin (1943), Grant (1944), and Gourlay (1955) and more recent reviews by Bradley (1963), Atiqullah (1967), Elashoff (1969) and Scheffe (1959, Ch. 10) can be extended and updated with recent research which provides closure to an area of active inquiry. (For a review of the effects of violation of the assumptions of the randomeffects ANOVA-a subject not reviewed here-the reader is directed to Scheffe, 1959, pp. 334-337 and Box & Anderson, 1962.) Asking whether ANOVA and ANCOVA assumptions are satisfied is not idle curiosity. The assumptions of most mathematical models are always false to a greater or lesser extent. The relevant question is not whether ANOVA assumptions are met exactly, but rather whether the plausible violations of the assumptions have serious consequences on the validity of probability statements based on the standard assumptions. Applied statistics in education and the social sciences experienced a largely unnecessary hegira to non-parametric statistics during the 1950s. Increasingly during the 1950s and early 1960s the fixed-effects, normal theory ANOVA was replaced by such comparable nonparametric techniques as the Wilcoxon test, Mann-Whitney U-test, Kruskal-Wallis one-way ANOVA, and the Friedman two-way ANOVA for ranks (Siegel, 1956). The flight to non-parametrics was unnecessary principally because researchers asked "Are normal theory ANOVA assumptions met?" instead of "How important are the inevitable violations of normal theory ANOVA assumptions?"
1,719 citations
TL;DR: MABA is sensitive, rapid, inexpensive, and nonradiometric and offers the potential for screening, with or without analytical instrumentation, large numbers of antimicrobial compounds against slow-growing mycobacteria.
Abstract: In response to the need for rapid, inexpensive, high-throughput assays for antimycobacterial drug screening, a microplate-based assay which uses Alamar blue reagent for determination of growth was evaluated. MICs of 30 antimicrobial agents against Mycobacterium tuberculosis H37Rv, M. tuberculosis H37Ra, and Mycobacterium avium were determined in the microplate Alamar blue assay (MABA) with both visual and fluorometric readings and compared to MICs determined in the BACTEC 460 system. For all three mycobacterial strains, there was < or = 1 dilution difference between MABA and BACTEC median MICs in four replicate experiments for 25 to 27 of the 30 antimicrobics. Significant differences between MABA and BACTEC MICs were observed with 0, 2, and 5 of 30 antimicrobial agents against H37Rv, H37Ra, and M. avium, respectively. Overall, MICs determined either visually or fluorometrically in MABA were highly correlated with those determined in the BACTEC 460 system, and visual MABA and fluorometric MABA MICs were highly correlated. MICs of rifampin, rifabutin, minocycline, and clarithromycin were consistently lower for H37Ra compared to H37Rv in all assays but were similar for most other drugs. M. tuberculosis H37Ra may be a suitable surrogate for the more virulent H37Rv strain in primary screening of compounds for antituberculosis activity. MABA is sensitive, rapid, inexpensive, and nonradiometric and offers the potential for screening, with or without analytical instrumentation, large numbers of antimicrobial compounds against slow-growing mycobacteria.
1,525 citations
Cites methods from "Principles and Procedures of Statis..."
...mine differences between the BACTEC system and the MABA either fluorometrically or visually for determination of MIC (18)....
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TL;DR: The efficiency of pigment extraction forms the crux of the spectrophotometric analysis of chlorophyll a and the alcoholic solvents, methanol and ethanol, proved to be superior to acetone and acetone with DMSO.
Abstract: The efficiency of pigment extraction forms the crux of the spectrophotometric analysis of chlorophyll a. The alcoholic solvents, methanol and ethanol, proved to be superior to acetone and acetone with DMSO. Homogenisation and sonication did not improve the extraction in the alcoholic solvents. Boiling at 100°C had an adverse effect whereas complete extraction of the pigments was obtained at the solvents boiling point and allowing the samples to stand for 24 h in the dark.
833 citations
01 Jan 1994
TL;DR: In this article, the authors describe protocols for testing freshwater organisms in the laboratory to evaluate the toxicity or bioaccumulation of contaminants associated with whole sediments, including the amphipod Hyalella azteca and midge Chironomus tentans.
Abstract: Procedures are described for testing freshwater organisms in the laboratory to evaluate the toxicity or bioaccumulation of contaminants associated with whole sediments. Sediments may be collected from the field or spiked with compounds in the laboratory. Toxicity methods are outlined for two organisms, the amphipod Hyalella azteca and the midge Chironomus tentans. The toxicity tests are conducted for 10d in 300-mL chambers containing 100 mL of sediment and 175 mL of overlying water. Overlying water is renewed daily and test organisms are fed during the toxicity tests. The endpoint in the toxicity test with H. azteca is survival and the endpoints in the toxicity test with C. tentans are survival and growth. Procedures are primarily described for testing freshwater sediments; however, estuarine sediments (up to 15% salinity) can also be tested with H. azteca. Guidance for conducting 28-d bioaccumulation tests with the oligochaete Lumbriculus variegatus is provided in this manual. Overlying water is renewed daily and test organisms are not fed during bioaccumulation tests. Methods are also described for determining bioaccumulation kinetics of different classes of compounds during 28-d exposures with L. variegatus.
819 citations
Cites background or methods from "Principles and Procedures of Statis..."
...The experimental unit is defined as the smallest physical entity to which treatments can be independently assigned (Steel and Torrie, 1980) and to which air and water exchange between test chambers are kept to a minimum....
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...4 The recommended procedure for pairwise comparisons that have a comparison-wise a error rate and equal replication is to do an ANOVA followed by a one-sided Fisher’s Least Significant Difference (LSD) test (Steel and Torrie, 1980)....
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...14.2.4.9.4 The recommended procedure for pairwise comparisons that have a comparison-wise a error rate and equal replication is to do an ANOVA followed by a one-sided Fisher’s Least Significant Difference (LSD) test (Steel and Torrie, 1980)....
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...The statistical methods discussed in this section are described in general statistics texts such as Steel and Torrie (1980), Sokal and Rohlf (1981), Dixon and Massey (1983), Zar (1984) and Snedecor and Cochran (1989)....
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...The experimental unit is defined as the smallest physical entity to which treatments can be independently assigned (Steel and Torrie, 1980) and to which air and water exchange between test chambers are kept to a minimum....
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TL;DR: This study focuses on the screening of effective PGPR strains on the basis of their potential for in-vitro auxin production and plant growth promoting activity under gnotobiotic conditions.
Abstract: A . K H A L I D , M . A R S H A D A N D Z . A . Z A H I R . 2004. Aims: Plant growth promoting rhizobacteria (PGPR) are commonly used as inoculants for improving the growth and yield of agricultural crops, however screening for the selection of effective PGPR strains is very critical. This study focuses on the screening of effective PGPR strains on the basis of their potential for in vitro auxin production and plant growth promoting activity under gnotobiotic conditions. Methods and Results: A large number of bacteria were isolated from the rhizosphere soil of wheat plants grown at different sites. Thirty isolates showing prolific growth on agar medium were selected and evaluated for their potential to produce auxins in vitro. Colorimetric analysis showed variable amount of auxins (ranging from 1AE 1t o 12AE 1m g l )1 ) produced by the rhizobacteria in vitro and amendment of the culture media with L-tryptophan (L-TRP), further stimulated auxin biosynthesis (ranging from 1AE 8t o 24AE 8m g l )1 ). HPLC analysis confirmed the presence of indole acetic acid (IAA) and indole acetamide (IAM) as the major auxins in the culture filtrates of these rhizobacteria. A series of laboratory experiments conducted on two cv. of wheat under gnotobiotic (axenic) conditions demonstrated increases in root elongation (up to 17AE3%), root dry weight (up to 13AE5%), shoot elongation (up to 37AE7%) and shoot dry weight (up to 36AE3%) of inoculated wheat seedlings. Linear positive correlation (r ¼ 0AE99) between in vitro auxin production and increase in growth parameters of inoculated seeds was found. Based upon auxin biosynthesis and growth-promoting activity, four isolates were selected and designated as plant growth-promoting rhizobacteria (PGPR). Auxin biosynthesis in sterilized vs nonsterilized soil inoculated with selected PGPR was also monitored that revealed superiority of the selected PGPR over indigenous microflora. Peatbased seed inoculation with selected PGPR isolates exhibited stimulatory effects on grain yields of tested wheat cv. in pot (up to 14AE7% increase over control) and field experiments (up to 27AE5% increase over control); however, the response varied with cv. and PGPR strains. Conclusions: It was concluded that the strain, which produced the highest amount of auxins in nonsterilized soil, also caused maximum increase in growth and yield of both the wheat cv. Significance and Impact of Study: This study suggested that potential for auxin biosynthesis by rhizobacteria could be used as a tool for the screening of effective PGPR strains.
785 citations
Cites methods from "Principles and Procedures of Statis..."
...The experimental data were analysed statistically according to Steel and Torrie (1980) and means were compared by Duncan’s Multiple Range Test (Duncan 1955)....
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...Correlations between in vitro auxin production by PGPR and effect on growth parameter(s) were also calculated (Steel and Torrie 1980)....
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