Developmental psychology.pdf

528 Psychology and Society
Row
Figure 19.18
Dvorak Keyboard. The typing is
largely in the home row and the
hands are used alternately. Further
information is available from the
Dvorak International^Federation at 11
Pearl Street, Brandon, Vermont
05733.
Upper
Home
Lower
7 5
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A 0
I Q
3 1 9 0 2 4 6
P Y F G С R
E U I D H Т N
J К X В M
W '
r-
V
8
s
Z
—
With regard to the use of letters within the rows, it should be remembered
that there are many one-handed sequences in the standard keyboard, in which speed
is one-half the maximum pace. Here is the second change in the Dvorak keyboard.
Both hands are more often used in coordination. While one hand is moving downward
to strike a letter, the other is moving upward into position to strike the next letter. To
achieve this condition, the letters in the home row have been assigned to be struck
alternately by each hand, the time of the downstroke for one hand being used for the
upstroke of the other (Figure 19.18).
In English, consonants often follow vowels and vice versa. Thus the letters are
assigned to the hands in accordance with this consonant-vowel alternation, and they
are assigned to the rows in accordance with usage. In the Dvorak keyboard the five
vowels, used very frequently, appear in the home row of the left hand, and five most
common consonants are in the home row of the right hand. Alternation is thereby
maximized, and the amount of typing is approximately balanced between the two hands.
To assess the value of this keyboard, statistical methods are indispensable. The
basic approach is to measure productivity with the standard keyboard and with the
Dvorak method and then to make a comparison, using words per minute as the chief
criterion. However, there are thousands of keyboard operators in the United States,
and all of these people cannot be included in the test. The investigator is thus faced
with the third and final major problem in statistics—the problem of statistical inference.
Descriptive statistics are used for describing a group of scores, all of which
are available to the investigator. Certain values, such as the mean and standard deviation,
indicate the performance of the whole group. Correlational methods indicate
the relationship between two sets of scores. The aim is to show the degree of association,
if any, between one variable and another. Finally, inferential statistics enable the
investigator to make an inference, or educated guess, about scores not obtained. A
sample is used to estimate the characteristics of a larger group. In this case we would
use a sample of Dvorak operators to make an inference about Dvorak operators in
general.
Problem of Estimation
Inferential statistics enable the investigator to hypothesize about subjects not included
in the research. One form of inferential statistics is called point estimation because the
investigator decides to what extent a certain value or point obtained with a group of
subjects probably is true about people in general. If we test 10 people on the Dvorak
Simplified Keyboard, is their mean score likely to reflect the mean of all Dvorakusers?
This question involves point estimation.
Point estimation is widely used in political polls. Very few potential voters are
questioned, yet the winner of the race is usually predicted successfully. In all such cases
the accuracy of the estimate depends partly upon which subjects are included in the
poll.