Accuracy refers to the closeness between measurements (observations)
and their expectations ("true" values). The farther a measurement is
from its expected value, the less accurate it is.
Precision pertains to the closeness to one another of a set of
repeated observations of a random variable. Thus, if such observations
are closely clustered together, then these observations are considered
to have been obtained with high precision.
More on Precision/Repeatability:
Good repeatability of a measurement (observations vary only a little
from the previous one) may indicate a precise instrument or measurement
technique but not necessarily an accurate one. In fact, an instrument
with a high resolution (the smallest discernible subdivision of an
instrument) could have poor repeatability indicating that the
instrument is not very precise and that the resolution is in fact
misleading. Similarly, a precise instrument may have a high resolution
but this should never be confused with it being accurate.
"I am for doing good to the poor, but I differ in opinion of the
means. I think the best way of doing good to the poor, is not
making them easy in poverty, but leading or driving them out of
it. In my youth I travelled much, and I observed in different
countries, that the more public provisions were made for the
poor the less they provided for themselves, and of course became
poorer. And, on the contrary, the less was done for them, the
more they did for themselves, and became richer." -- Benjamin
Franklin, /The Encouragement of Idleness/, 1766
Consider it a public service announcement.
No question anywhere, but from a couple of posts in recent weeks where
the terms were used interchangeably I thought it might be helpful to go
over the basics.
Sorry for boring those who already know this stuff backwards and forwards.
It's worth while repeating it every now and then but it probably
won't do any good. It's like explaining the difference between
"there" and "their" or "site" and "sight" the folks that post
on newsgroups and bulletinboards don't bother with such mundane
things. Their response is nearly always "You know (sometimes no)
what I mean". :-)
I know what you mean, "they're", "their", "there", plus "cite",
"site", and "sight" can get confused. But realistically speaking,
we're metal workers not English majors so the occasional grammatical
gaffe is to be expected.
The pressing question of the moment is; should the period come after
or before the end quotation mark? LOL
Pretty cool. I bet you're the life of the party at all those grammar
From my Merriam Webster's "Guide to Punctuation and Style" 1995
edition on page 48, "A period is place within quotation marks even when
it does not punctuate the quoted material."
Personally, I sometimes put the period on the outside, sometimes on
the inside, kind of randomly. But after reading the "Guide" I better
straighten up and fly right - and put them on the inside from now on.
Given all the other grammatical boo-boos I'm surely making, an
accurate or precise period placement is probably a minor offense.
These are not exactly as I would describe it -
Accuracy - the degree to which the measured value matches the true value
Precision - the resolution of measurement - number of significant digits -
precision must be greater than or equal to accuracy
repeatability - the degree to which successive measurements of the same
exact object return the same value
so, my understanding of precision seems to differ from yours ** Posted from
I couldn't resist , as misusing words is also one of my pet peeves . To ,
too , two also comes to mind , as does cede, seed . And outta instead of
oughta really grates on the one great nerve I have left !
I did not know that the period always goes inside ... might have at some
point , but not being a wordsmith (cabinetmaker , hobby machinist) I tend to
forget things like that .
Well let's take a look at what some other sources have to say.
If you repeat a measurement several times on the same parameter over
the period of measurement, you may get a series of readings that differ
from each other. The cause may be small differences in how you use the
instrument each time. The differences could also be due to random
changes in the instrument, and they could be due to small changes in
the parameter you are measuring. Whatever the cause, you would be
inclined to take the average of the readings as the best value you can
quote or use. You can get an idea of the variability from the range of
values obtained, i.e. the difference between the largest and smallest
reading, but a better measure is likely to be the variance of the
readings. Variance, var, is a statistical measure obtained by calculating:
Accurate means "capable of providing a correct reading or
measurement." In physical science it means 'correct'. A measurement is
accurate if it correctly reflects the size of the thing being measured.
Precise means "exact, as in performance, execution, or amount. "In
physical science it means "repeatable, reliable, getting the same
measurement each time."
Accuracy refers to the agreement between a measurement and the true or
correct value. If a clock strikes twelve when the sun is exactly
overhead, the clock is said to be accurate. The measurement of the
clock (twelve) and the phenomena it is meant to measure (The sun
located at zenith) are in agreement. Accuracy cannot be discussed
meaningfully unless the true value is known or is knowable. (Note: The
true value of a measurement can never be known. Read more about this.)
Accuracy refers to the agreement of the measurement and the true value
and does not tell you about the quality of the instrument. The
instrument may be of high quality and still disagree with the true
value. In the example above it was assumed that the purpose of the
clock is to measure the location of the sun as it appears to move
across the sky. However, in our system of time zones the sun is
directly overhead at twelve O'clock only if you are at the center of
the time zone. If you are at the eastern edge of the time zone the sun
is directly overhead around 11:30, while at the western edge the sun is
directly overhead at around 12:30. So at either edge the twelve O'clock
reading does not agree with the phenomena of the sun being at the local
zenith and we might complain that the clock is not accurate. Here the
accuracy of the clock reading is affected by our system of time zones
rather than by any defect of the clock.
In the case of time zones however clocks measure something slightly
more abstract than the location of the sun. We define the clock at the
center of the time zone to be correct if it matches the sun, we then
define all the other clocks in that time zone to be correct if they
match the central clock. Thus a clock at the Eastern edge of a time
zone that reads 11:30 when the sun is overhead would still be accurate
since it agrees with the central clock. A clock that read 12:00 would
not be accurate at that time. The idea to get used to here is that
accuracy only refers to the agreement between the measured value and
the expected value and that this may or may not say something about the
quality of the measuring instrument. A stopped clock is accurate at
least once each day.
Precision refers to the repeatability of measurement. It does not
require us to know the correct or true value. If each day for several
years a clock reads exactly 10:17 AM when the sun is at the zenith,
this clock is very precise. Since there are more than thirty million
seconds in a year this device is more precise than one part in one
million! That is a very fine clock indeed! You should take note here
that we do not need to consider the complications of edges of time
zones to decide that this is a good clock. The true meaning of noon is
not important because we only care that the clock is giving a
The precision of an instrument reflects the number of significant
digits in a reading;
The accuracy of an instrument reflects how close the reading is to the
'true' value measured.
This last one above seems to support your perspective.
Here's what it says:
3. The first word of a direct quotation is capitalized. However, if
the quotation is interrupted in mid-sentence, the second part does not
begin with a capital.
Example: The President said, "We have rejected this report entirely."
"We have rejected this report entirely," the President said, "and we
will not comment on it further."
4. When a quotation, whether a sentence fragment or a complete
sentence, is syntactically dependent on the sentence in which it
occurs, the quotation does not begin with a capital.
Example: The President made it clear that "there is no room for
Geeze, no more questions that entail transcription, PLEASE!