Question

Regressions of the resulting (log10) cob dry-biomass and (logo) total plant dry-biomass (cob + rest- of-plant) data produced the following: Maize Crop 1: r=0.8, p = 0.034;y-intercept = -0.23, p = 0.01; slope = 0.78, p = 0.049 Maize Crop 2:r = 0.6, p = 0.006, y-intercept = -0.031, p = 0.009; slope = 1.23, p < 0.001 An Analysis of Covariance (ANCOVA) of your data produced the following: Intercept: p < 0.13; Slope: p <0.04. Is there statistically-robust evidence of phenotypic plasticity in allocation to cobs versus the rest of the maize plant (shoots + roots) in standard maize crops? Explain. Answer:

Answer 1

First of all, the information given in this question is not complete. The following information is acking:

1. It is not given as to what is the covariate that is used in this calculation.

2. In the question above, it was clear that the regression was done by taking (log10)cob dry biomass as dependent variable and (log10)total plant dry-biomass(cob+rest of the plant). This regression was performed for maize crop 1 and maize crop 2.

3. For deciding whether the regression model fitted well or not, we need to use the r which is the correlation between x and y. A better value of the model fit could have been R^2 which is not given.

Maize crop 1 and 2: From the data, it is evident that the model fitted well with r=0.8(p=0.034) which indicates that there is high degree of liner relationship. Both the intercept and slope p-values are also statistically significant indicating that the intercept cannot be assumed zero and slope cannot be assumed to be 1.

4. It is not distinctly clear as to what is the covariate measurement in this case. Also, it is not clear that the results are for what crop(crop1 or crop 2).

Let us assume that the results are done for crop1. Then it is obvious that by including the covariate, the intercept p-value changed but it is still significant at 13% level of significant. In this case, the results are mostly unchanged by including the covariates. The same argument also hold good if we assume crop2 as well.

Owing to the partal or lack of information it cannot be inferred about phenotypic plasticity.