Principles and procedures of statistics: McGraw-Hill Book Company, Inc. New York Toronto London.
01 Jan 1960-
About: The article was published on 1960-01-01 and is currently open access. It has received 5154 citations till now.
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TL;DR: Suggestions are offered to statisticians and editors of ecological journals as to how ecologists' under- standing of experimental design and statistics might be improved.
Abstract: Pseudoreplication is defined. as the use of inferential statistics to test for treatment effects with data from experiments where either treatments are not replicated (though samples may be) or replicates are not statistically independent. In ANOVA terminology, it is the testing for treatment effects with an error term inappropriate to the hypothesis being considered. Scrutiny of 176 experi- mental studies published between 1960 and the present revealed that pseudoreplication occurred in 27% of them, or 48% of all such studies that applied inferential statistics. The incidence of pseudo- replication is especially high in studies of marine benthos and small mammals. The critical features of controlled experimentation are reviewed. Nondemonic intrusion is defined as the impingement of chance events on an experiment in progress. As a safeguard against both it and preexisting gradients, interspersion of treatments is argued to be an obligatory feature of good design. Especially in small experiments, adequate interspersion can sometimes be assured only by dispensing with strict random- ization procedures. Comprehension of this conflict between interspersion and randomization is aided by distinguishing pre-layout (or conventional) and layout-specifit alpha (probability of type I error). Suggestions are offered to statisticians and editors of ecological j oumals as to how ecologists' under- standing of experimental design and statistics might be improved.
7,808 citations
TL;DR: In this paper, the effect of age on optimal body weight is controversial, and few studies have had adequate numbers of subjects to analyze mortality as a function of body-mass index across age groups.
Abstract: Background The effect of age on optimal body weight is controversial, and few studies have had adequate numbers of subjects to analyze mortality as a function of body-mass index across age groups. Methods We studied mortality over 12 years among white men and women who participated in the American Cancer Society's Cancer Prevention Study I (from 1960 through 1972). The 62,116 men and 262,019 women included in this analysis had never smoked cigarettes, had no history of heart disease, stroke, or cancer (other than skin cancer) at base line in 1959–1960, and had no history of recent unintentional weight loss. The date and cause of death for subjects who died were determined from death certificates. The associations between body-mass index (defined as the weight in kilograms divided by the square of the height in meters) and mortality were examined for six age groups in analyses in which we adjusted for age, educational level, physical activity, and alcohol consumption. Results Greater body-mass index was as...
1,513 citations
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
TL;DR: Comparison of neonatal production with ingestion and assimilation suggests that larger mammals put proportionately less effort into reproduction.
Abstract: Patterns in life history phenomena may be demonstrated by examining wide ranges of body weight. Positive relationships exist between adult body size and the clutch size of poikilotherms, litter weight, neonate weight life span, maturation time and, for homeotherms at least, brood or gestation time. The complex of these factors reduces r
max in larger animals or, in more physiological terms, r
max is set by individual growth rate. Comparison of neonatal production with ingestion and assimilation suggests that larger mammals put proportionately less effort into reproduction. Declining parental investment and longer development times would result if neonatal weight is scaled allometrically to adult weight and neonatal growth rate to neonatal weight. Body size relations represent general ecological theries and therefore hold considerable promise in the development of predictive ecology.
753 citations