Figure 1
The 8 possible constructions of an X-mark. The points of the arrows show the stroke direction, while the size represents the stroke sequence: the heavy arrow being traced first, and the light one being traced second.
Figure 2
Illustration of the questioned X-mark.
Table 1
Results of the empirical study carried out within a population of 100 writers. #1 to #8 represent the 8 possible constructions of an X-mark, depending on the sequence and direction of the strokes (see Figure 1).
| #1 | #2 | #3 | #4 | #5 | #6 | #7 | #8 | Total | |
|---|---|---|---|---|---|---|---|---|---|
| Left-handed writers | 9 | - | - | - | 12 | 4 | - | - | 25 |
| Right-handed writers | 19 | - | 17 | - | 34 | - | 5 | - | 75 |
| Total | 28 | - | 17 | - | 46 | 4 | 5 | - | 100 |
Figure 3
The four construction classes of an X-mark, based on the direction of the strokes. The points of the arrows show the stroke direction.
Table 2
Prior counts, observations and posterior counts of the construction classes of X-marks in populations of right and left-handed writers. The observations result from the experimental study carried out for the needs of the case (see Table 1), grouping constructions #1 and #5 in class A, #2 and #6 in class B, #3 and #7 in class C, #4 and #8 in class D. Posterior counts represent the sum of the prior counts with the observations.
| Right-handed writers | Left-handed writers | ||||
|---|---|---|---|---|---|
| Outcome | Prior counts | Observations | Posterior counts | Observations | Posterior counts |
| A | 1 | 53 | 54 | 21 | 22 |
| B | 1 | 0 | 1 | 4 | 5 |
| C | 1 | 22 | 23 | 0 | 1 |
| D | 1 | 0 | 1 | 0 | 1 |
| Total | 4 | 75 | 79 | 25 | 29 |
Table 3
Probabilities of observing a given construction class if the writer is a right or a left-handed writer.
| Outcome | Probability of a given construction class if the writer is right-handed | Probability of a given construction class if the writer is left-handed |
|---|---|---|
| A | P(A|R) = 54/79 | P(A|L) = 22/29 |
| B | P(B|R) = 1/79 | P(B|L) = 5/29 |
| C | P(C|R) = 23/79 | P(C|L) = 1/29 |
| D | P(D|R) = 1/79 | P(D|L) = 1/29 |