Need Question Answered

Andrew Mitz arm at helix.nih.gov
Mon May 10 16:04:03 EST 1993

In article <9305080126.AA59210 at itsa.ucsf.EDU> jharper at ITSA.UCSF.EDU (M. Jane Harper) writes:
>On 6 May 93 ltorre at eis.calstate.edu asked:
>>Can someone out there help me distinguish between the scientific terms:
>>		-Accuracy
>>		-Reliability
>>		-Validity
>"Accuracy" is not a technical measurement term which, to my knowledge, has a
>meaning outside its common one.  "Reliability" means the extent to which an
>instrument reproduces results given the same analysand.  In other words, if
>you and I (or Machine A and Machine B) rate someone (or some thing) on a
>characteristic and we get identical or closely correlated results, the tool
>we used to perform the rating has a high reliability.  "Validity" is a related
>concept which refers to the extent to which an instrument measures what it is
>intended to measure.  If I stick a thermometer in someone's mouth, I will get
>a temperature, not a blood pressure; the thermometer is a valid measure of
>temperature and an invalid measure of blood pressure.

Good answer.  Let me add that sometimes Accuracy is used to distinguish from
precision.  In this case, precision means the same as "reliability" as defined
above.  Accuracy would mean the difference between a measurement and the
actual value being measured.  Rarely is the actual value known, but sometimes
it is.  For example, if I have 100 pennies (measured by counting), and I use
a device that measures the number of pennies by using their weight, I could
test the accuracy of the device.  

Andrew Mitz          |    NIH Animal Center  | Opinions are mine alone |
Biomedical Engineer  |    Poolesville, MD    | arm at helix.nih.gov       |

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