F values and T values
Quick reference
To calculate and print an F value and a triangle of T values for a group of columns, type:
nft
as an element in the axis.
More information
The nft element creates an F value and a triangle of T values for groups of columns. A group of columns starts at a base or n23 statement and continues until another base or n23 is read, or until the end of the axis, whichever is sooner. Columns that are non-totalizable (such as, n04, n05, n12) and columns that are not printed are ignored. Quantum also ignores any groups of columns that contain fewer than two elements that are included in the calculation.
The nft element is meaningful only in row axes and is therefore ignored in column or higher dimension axes. It is specified as nft with no row text or options.
With ordinary formatted output, the F value for a group is printed under the middle of that group. With PostScript output, it is printed under the right-most column in the group. The probability, expressed as a percentage, is printed underneath the F value.
The triangle of T values is lined up with the values in the columns to which they refer. The probability for each T value, expressed as a percentage, is printed underneath the corresponding T value. Asterisks are printed down the leading diagonal of T values.
Example
Here’s a spec and the table it produces. The spec is:
tab rating age
l rating
col 45;Base;Excellent;%fac=2-1;Very Good;Satisfactory;Poor;Very poor
nft
l age
col 9;Base;18-30;31-44;45-54;55+
g Base 18-30 31-44 45-54 55+
g ---- ----- ----- ----- ----
p x x x x x
and the table it produces is:
Base 18-30 31-44 45-54 55+
---- ----- ----- ----- ----
Base 340 65 93 76 70
Excellent 95 21 20 28 16
Very Good 21 4 5 7 5
Satisfactory 70 15 21 15 19
Poor 69 14 21 17 17
Very poor 49 11 21 9 13
F stat 2.40
F prob 6.55
T stat * -1.47 0.85 -0.95
T prob 14.03 39.30 34.06
T stat * 2.50 0.52
T prob 1.26 60.51
T stat * -1.92
T prob 5.68
T stat *
T prob |
See also