Validity
a valid measurement is a quantity or dimension that corresponds to the measured variable
there are standard measurements (procedures and expressions) for common variables, but where variables must be are operationally defined, or surrogate variables used because they are more easily measured, then the validity of measurements has to be ensured
Accuracy
closeness of measurements to an expected or true value
accuracy is inversely proportional to error (i.e. high accuracy corresponds to low error)
types of error:
gross: blunders caused by carelessness of instrument failure
systematic: consistent overestimation or underestimation of the target value; usually caused by poor calibration of an instrument or a poor measurement procedure; often small enough to go undetected by results in a poor inference of a target value
random: human error randomly (normally) distributed with respect to the mean observation
Precision
the closeness of repeated measurements to one another
Sampling