Need Question Answered

Steven L. Wertheim stevew at
Thu May 13 11:07:08 EST 1993

>>On 6 May 93 ltorre at asked:
>>>Can someone out there help me distinguish between the scientific terms:
>>>		-Accuracy
>>>		-Reliability
>>>		-Validity

>In article <9305080126.AA59210 at itsa.ucsf.EDU> jharper at ITSA.UCSF.EDU (M. Jane Harper) writes:
>>"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.

In article <1993May10.210403.4926 at> arm at (Andrew Mitz
) writes:>
>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.

Just one more clarification to the many excellent reponses.  Precision is the
smallest numerical gradation that a device can measure.  This says nothing
about its accuracy.  If the thermometer above has a marking every .1 degrees,
but has the wrong amount of mercury inside, it still has .1 degree precision
even though it may be (reliably) several degrees off (inaccurate).


Steven L. Wertheim, Ph.D.                       Internet: stevew at
Harvard Medical School                         Voice-net: (508) 624-8117 
New England Regional Primate Research Center         Fax: (508) 624-8075    
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