Missing Values in Experiments Analysed on Automatic Computers

Healy, M. J. R.; Westmacott, M. H.

doi:10.2307/2985421

Cited by 147 publications

(73 citation statements)

References 2 publications

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“…Perfect homogeneity-would give an e of one, but the e values were all less than one, causing an increase in the critical i^-value. The ANOVA was modified for missing values using the method of Healy & Westmacott (1956, Genstat 5 Committee, 1989, …”

Section: Discussionmentioning

confidence: 99%

Physiological integration among tillers of Holcus lanatus: age‐dependence and responses to clipping and competition

1994

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S L" M M . A R YThe ecolQgical consequences of physidlogical ititegraticin among tillers were examined in a glasshouse experiment on the clonal grass Holcus Itinatu! L. We measured the effects of se\ ering the internode connettion hetween a tilier and its parent on the growth and survival of this marked tiller. 7'he effects of three factors on the response to severing were determined using this procedure •. competition with the parent plant, by cotnpating tillers repotted in isolation with tillers remaining in the neighhourhood of the parent; clipping treatment, comprising no clipping, clipping only the marked tiller and its daughter tiliers or clipping the whole parent plant, including the marked tiller; and the change in the response with tiller age at severing, using four tiller ages (1, 2, 4-and 8 wk). These age, clipping and sL'\ering treatments were applied factorially.After K wk of growih the responses to se\ ering of the marked tillers were dependent on the age and clipping treatmetits. Severttig always decreased sur\i\"al atid growth (ttller production, biomass and tiller extension) of the youngest tillers (ages 1 and 2 wk), indicating that they were dependent on the parent to support their early growth. Age 4 tillers were able to support their own growth and grew best in isolation; but when grown in the parent's neighbourhood competition with the parent reduced growth, aithough parental support ameliorated these effects. Some of the oldest tillers (age 8 wk) showed decreased growth when unsevered. This indicated an outflow of resources to the parent and suggested that integration allowed the control and coordination of tiller growth.The pattern of the severing effects was similar in all clipping treatments, \arying only in degree. There was little evidence of increased support for clipped tillers or for a change in the pattern of integration when the whole plant was clipped, except that age 8 tillers showed a continued henefirof the connection, in contrast to the positive effect of severing in the other tw o clipping treatmetits. The extension rate of the marked tiller showed complex responses to clipping and se\ eritig treatments, including effects of integration on regrowth after clipping. This experiment has shown that the growth of tillers in H. lanatus is highly integrated hut that this mtegratinn is extremely plastic in response to tiiler age and, to a lesser extent, clipping treatment.

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Section: Discussionmentioning

confidence: 99%

Physiological integration among tillers of Holcus lanatus: age‐dependence and responses to clipping and competition

1994

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“…Entry means and error mean squares were used for further combined analyses of variance (Cochran and Cox, 1957). Outliers were detected according to Anscombe and Tukey (1963) and if significant at P= 0.05, they were declared to be missing values and estimated using the iterative method of Healy and Westmacott (1956). There were less than 1% of outliers in the whole data set.…”

Section: Methodsmentioning

confidence: 99%

Manganese and zinc concentrations in maize genotypes grown on soils differing in acidity

Rastija

Kovačević

Rastija

et al. 2010

Acta Agronomica Hungarica

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Drought and soil acidity are two major abiotic stress factors limiting maize production worldwide, generating imbalances in the manganese (Mn) and zinc (Zn) status in plants. This study was conducted to determine the effects of drought stress on the Mn and Zn status in maize genotypes grown on acid and non-acid soils and how the Mn and Zn status affects the changes in grain yield caused by drought stress and soil acidity. Seventeen genotypes were grown at two locations differing in soil acidity in Eastern Croatia in 2003 and 2004. Positive values of an aridity index indicated drought stress in 2003. The genotypes had much higher Mn and Zn concentrations on acid soil than on nonacid soil: more than twice as high in both seasons for Zn and about 6 and 9 times higher in normal and in dry seasons, respectively, for Mn. This demonstrates that drought combined with soil acidity led to the excessive accumulation of Mn in maize plants. However, variation was observed between the maize genotypes for the Mn accumulation on soils differing in acidity when drought occurred. Some genotypes accumulated Mn on acid soil irrespective of drought. The Mn and Zn status had no discernible effect on the changes in grain yield caused by drought stress and/or soil acidity.

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“…In some articles such as those concerned with the multivariate normal (Afifi & Elashoff, 1966; Anderson, 1957;Hartley & Hocking, 1971;Hocking & Smith, 1968;Wilks, 1932), "missing at random" seems to mean that each item in the data matrix is equally likely to be missing. In other articles such as those dealing with the analysis of variance (Hartley, 1956;Healy & westmacott, 1956;Rubin, 1972;Wilkinson, 1958), "missing at random" seems to mean that observations of the dependent variable are missing without regard to the actual values that would have been observed. Similarly, "missing at random lt apparently can mean missing according to a preplanned experimental design (Hocking & Smith, 1972-;Trawinski & Bargmann, 1964).…”

Section: "Missing At Random" As Used In the Literaturementioning

confidence: 99%

Missing at Random ‐ What Does It Mean?

Rubin

1973

ETS Research Bulletin Series

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Most articles on missing values assume the missing data are “missing at random” and ignore the process that “caused” the missing values. The condition under which this procedure is justified is explored here: the concept of missing at random is precisely defined, several examples are discussed, and two simple conditions are given which are sufficient to assure that the missing data are missing at random.

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Missing Values in Experiments Analysed on Automatic Computers

Cited by 147 publications

References 2 publications

Physiological integration among tillers of Holcus lanatus: age‐dependence and responses to clipping and competition

Physiological integration among tillers of Holcus lanatus: age‐dependence and responses to clipping and competition

Manganese and zinc concentrations in maize genotypes grown on soils differing in acidity

Missing at Random ‐ What Does It Mean?

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