Accuracy, precision, validity and reliability

In public health the terms accuracy, precision, validity and reliability mean the following:

Accuracy: The degree to which a measurement represents the true value of something. Simply put: How close a measurement is to the true value

Precision: The degree of resemblance among study results, were the study to be repeated under similar circumstances.                                                                          Simply put: How close the measurements are to each other

Lack of precision is referred to as ‘random error‘.

Validity:  The extent to which the study measures what it is intended to measure.       Simply put: Are the values describing what was supposed to be measured?

Internal validity: Are the results valid for the study subjects?

External validity (Generalizability): Are the results valid for the population from which the sample was drawn?

Lack of validity is referred to as ‘Bias‘ or ‘systematic error‘.

Reliability: A measure of how dependably an observation is exactly the same when repeated. It refers to the measuring procedure rather than to the attribute being measured. Simply put: Will one get the same values if the measurements are repeated? 

Note: Many authors use the terms in the following sense:

Accuracy (validity): Validity and accuracy are used synonymously

Precision (reliability): Precision and reliability are used synonymously

1. https://books.google.co.in/books?id=Hb9xV2KA0m4C&pg=PA69&lpg=PA69&dq=accuracy+precision+and+reliability+public+health&source=bl&ots=8P4xaXUnsy&sig=u9-OCSQBYKML9CbKkaAxKfMmkaA&hl=en&sa=X&ei=11mJVc3SJo7JuASCrYO4Cw&redir_esc=y#v=onepage&q=accuracy%20precision%20and%20reliability%20public%20health&f=false

2. https://books.google.co.in/books?id=sXz_3_YgMFQC&pg=PA5&lpg=PA5&dq=accuracy+precision+and+reliability+public+health&source=bl&ots=5V2AljJZoh&sig=cEu5tOawpXPy5nXwlDQ_irtubyE&hl=en&sa=X&ei=11mJVc3SJo7JuASCrYO4Cw&redir_esc=y#v=onepage&q=accuracy%20precision%20and%20reliability%20public%20health&f=false

3. https://books.google.co.in/books?id=rr7UHzVid-0C&pg=PT26&lpg=PT26&dq=accuracy+precision+and+reliability+public+health&source=bl&ots=UfuliQJRwt&sig=M1H7IkPAsi77qbeT-JvQi-TOM_8&hl=en&sa=X&ei=pVeJVZy7NIGXuATyo7TADQ&redir_esc=y#v=onepage&q=accuracy%20precision%20and%20reliability%20public%20health&f=false

4. https://books.google.co.in/books?id=3Zp5AAAAQBAJ&pg=PA81&lpg=PA81&dq=accuracy+precision+and+reliability+public+health&source=bl&ots=j5tAzqmfp6&sig=ItlgXxMWlNZrRkbWVtk0nN7nTzM&hl=en&sa=X&ei=11mJVc3SJo7JuASCrYO4Cw&redir_esc=y#v=onepage&q=accuracy%20precision%20and%20reliability%20public%20health&f=false

5. https://books.google.co.in/books?id=Cpk65cya9HcC&pg=PA314&lpg=PA314&dq=accuracy+precision+and+reliability+public+health&source=bl&ots=kme4XuUu9i&sig=TmmKqgvMRHjhCfB4b5teHLjCKxY&hl=en&sa=X&ei=11mJVc3SJo7JuASCrYO4Cw&redir_esc=y#v=onepage&q=accuracy%20precision%20and%20reliability%20public%20health&f=false

However, this article should help clarify the matter:

http://www.ncbi.nlm.nih.gov/pubmed/16549250

Useful Link:

Link to YouTube video explaining the concepts:

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