1. The basic variable: column heading
These variables refer directly to columns in the spreadsheet. The name of the variable is the heading you enter for the column in the spreadsheet.
If you have the following data in the spreadsheet:
then ID_NR, TREATMENT, AGE, HEIGHT and WEIGHT are valid variables.
Remember that a variable name should not include spaces, nor the following characters: - + / * = < > ^ ( ) [ ] $ " ' : ,. In addition, the variable name should not start with a number and it must be different from reserved words such as TRUE, FALSE, ROW and COLUMN. Finally, it should not be equal to the address of a spreadsheet cell such as A1, S1, AB35, IL6, etc.
2. Combination of variables
When performing statistical analyses or creating graphs, you can enter a combination of variables as a variable in the dialog panels:
In this example, the variables WEIGHT and HEIGHT are combined into a new variable (the Body Mass Index) with the formula WEIGHT/(HEIGHT*HEIGHT). Any of the following operators can be used to combine variables (in order of precedence):
|* /||Multiplication, Division|
|+ -||Addition, subtraction|
As shown in the example, brackets can be used to change the operators precedence.
3. Transformation of a variable
When a variable needs transformation, you can use one of the many MedCalc spreadsheet functions. For example, if a variable needs square root transformation you use the SQRT(variable) function as new variable:
- The formula WEIGHT/(HEIGHT*HEIGHT) can also be written using the POWER function as: WEIGHT/POWER(HEIGHT,2)
- there is no space between the function name SQRT, POWER, etc., and the opening bracket (.
- when a function requires more than one argument, these arguments are separated by the list separator that is selected in the Windows settings (Control panel - Regional settings - Number). Usually this is a comma (as in the examples in this help file), but in European countries the list separator commonly is a semicolon ";". In the latter case, the above example should be written as: WEIGHT/POWER(HEIGHT;2).