Data management

Note how the data are organised in CS15Data1 and CS15Data2. Open these files. The first column contains the plot number. This is followed by the number of the block in which the plot resides and then each of the factors: level of spacing, whether or not fertiliser was applied, and the cultivar. CS15Data1 also contains week number. These columns are followed by columns containing the values recorded for each of the variables. Both files have been entered into GenStat, tidied up and stored as Excel files. Note how many decimal places are recorded for biomass and grain yield in CS15Data2 and height and number of leaves in CS15Data1. Values have been derived from raw measurements. Thus they have been recorded with a suitable number of decimal places consistent with the likely precision of measurement. Harvest index is derived from grain yield and biomass and so shows more decimal places.

The numbers of decimal places in CS15Data1 are not fixed (* is the default in GenStat and also Excel). This means that data are presented up to the last non-zero digit. Thus, the average height of plants in plot number 8 is presented as 12, rather than 12.0. This is not a particularly useful way to present the data for it makes it more difficult to check by eye that the data have been entered correctly in the spread sheet. It would have been better for all height values to have been presented with one decimal place. GenStat has a useful Spread → Column → Attributes/Format... command (the same can be achieved by right clicking a column heading) that allows the numbers of decimal places to be changed and also the width of the column. Thus, by using this command for the variable Biomass in CS15Data2 all values can be made to have the same number of places, namely two.

CS15Data1 is presented in plot number order. The data in CS15Data2 have been sorted into factor level order. Some researchers feel that data have to be presented in treatment order for statistical analysis. This is not true, certainly in the case of GenStat. This program can handle data presented in any order. It is much better to leave the data in the order that they have been entered, as in CS15Data1, for this means that the data in the spread sheet can at any time be compared with the values written in the experimental recording sheet.