(b) Calling.
Sometimes when the observer has his hands full
making the observation, he is unable to record the data. At such times, he
calls out his readings to an assistant, who records the information.
The
caller's voice should be clear and sharp, and the assistant should have good
hearing.
In more complex experiments, two observers may call readings to
one recorder, especially when simultaneous readings are needed. When a more
complete record is required, a tape recording can be made and the data
transcribed, or rechecked later.
(c) Writing. Anyone who records data of any importance should be
able to write clearly and sharply.
The characters should be legible,
uniform, and in proper alinement. This is no place for a person who makes
chicken tracks for numbers.
(d) Forms.
Many laboratory procedures have the aspect of
repetition; hence, the use of appropriate forms is a labor-saving device as
well as an error-preventing technique. Forms should be clearly titled with
spaces for all pertinent information as well as the measurement readings.
Columns should be headed with titles.
Sometimes the processes or the
mathematics involved are indicated by the layout of the form. There should
be general purpose forms as well as those specific to a particular
calibration. When a form is not available, it is better to improvise one
rather than to use a blank sheet of paper.
(4) Weighting data.
(a) At times, you may encounter a set of data which is made up of
values all of which are not equally trustworthy. It would be incorrect to
give them equal weight when averaging, yet you may not feel like
disregarding the doubtful readings. You can improve the probability of the
validity of the average by a process of weighting. The formula is:
(b) For example, let us say that the following readings were made:
81, 83, 85, 89, and 96. Due to the conditions of measurement, it is felt
that the 83 and 85 measurements are three times as likely to be accurate at
the 81 and 89, which are twice as likely to be accurate as the 96. Thus we
want to weight 83 and 85 at 6, weight 81 and 89 at 2, and weight 96 at 1.
Set it up as follows:
(c) This process allows the low-probability values to influence
the average but not as much as the high-probability values.
The
statistician can assign any weights he feels are appropriate.
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