Developmental psychology.pdf

Technology and Statistics 523
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Letters
Figure 19.10
Letter Usage. This graph represents
the average scores from the four
samples in the survey. To make
comparisons easier, all totals were
proportionately raised to the base of
one thousand for E, the most
common letter (Hoke, 1922).
These data showed that the letters are used with very different frequencies.
The letter E is employed more often than twelve other letters of the alphabet combined.
The six most common letters account for more than half of all letter usage, as is readily
apparent in a graphic display (Figure 19.10).
Numerical Data The next step, after determining the work, was to measure the
workers' capabilities, and the investigators in this instance focused only on finger
dexterity, assuming adequate mental skills. Adult males and females were tested by
having them tap in various ways on the machine and on a table, with the wrist stationary.
The first question concerned the typical scores, and therefore the mean tapping
rate was calculated for all eight fingers, excluding the thumbs. The right index
finger was found most capable, followed by the left index finger. Next were the middle
fingers, then the little fingers, and finally the ring fingers, with the right fingers superior
to the left in each instance (Hoke, 1922).
Then came the question of variability. How consistent were the different fingers?
Was one more variable than another? It turned out that consistency was not an
issue. The standard deviations showed no significant variation among the fingers
(Figure 19.11).
In describing a set of scores, the mean and standard deviation are generally
reported together, conveying information about central tendency and variability. In the
case of finger ability, the fingers differed in mean rate but not in variability of tapping
rate. No one of them was markedly more variable, or less predictable, than the others.
Finger Mean S.D.
Right index
Left index
Right middle
Left middle
Right little
Left little
Right ring
Left ring
161.2
149.9
134.3
120.8
114.8
105.9
101.4
98.6
25.0
24.6
25.9
26.0
27.5
29.7
29.9
25.5
Figure 19.11
Finger Abilities. The fingers are
ranked from fastest to slowest
according to mean rate of tapping.
There are relatively small differenceb
in variability, as indicated by the
standard deviations (Hoke, 1922)