Question  Answer 

Validity (or measurement)  The extent to which data obtained from measurement are directly relevant to the target behaviour of interest and to the reasons for measuring it 
Accuracy (of measurement)  The extent to which observed values, the data produced by measuring an event, match the true state, or true values, of the event as it exists in nature. 
Observed Value  A measured produced by an observation and measurement system. Observed values serve as the data that the researcher and others will interpret to form conclusions about an investigation. 
True Value  A measure accepted as a quantitative description of the true state of some dimensional quantity of an event as it exists in nature. 
Obtaining true values requires "special or extraordinary precautions to ensure that all possible sources of error have been avoided or removed? (Compare with Observed Value)  
Measurement Bias  Nonrandom measurement error; a form of inaccurate measurement in which the data consistently overestimate or underestimate the true value of the environment. 
Reliability (of measurement)  Refers to the consistency of the measurement, specifically, the extent to which repeated measurement of the same event yields the same values. 
Direct Measurement  Occurs when the behaviour that is measured is the same as the behaviour that is the focus of the investigation. 
Indirect Measurement  Occurs when the behaviour that is measured is in some way different from the behaviour of interest; considered less valid than 
direct measurement because inferences about the relation between the data obtained and the actual behaviour of interest are required  
Continuous Measurement  Measurement conducted in a manner such that all instances of the response class(es) of interest are detected during the observation period. 
Discontinuous Measurement  Measurement conducted in a manner such that some instances of the response class(es)of interest may not be detected 
Observer Drift  Any unintended change in the way an observer uses a measurement system over the course of an investigation that results in measurement error; 
often entails a shift in the observers interpretation of the original definitions of the target behaviour subsequent to being trained.  
naive observer  An observer who is unaware of the study's purpose and/or the experimental conditions in effect during a given phase or observation period. Data obtained by a naive observer are less likely to be influenced by observers' expectations. 
Observer Reactivity  Influence on the data reporter by an observer that results from the observers awareness that others are evaluating the data he reports. 
Calibration  Any procedure used to evaluate the accuracy of measurement system and, when sources of error are found, to use that information to correct or improve the measurement system 
Interobserver Agreement (IOA)  A measure of temporallocus; defined as the elapsed time between two successive responses 
Scored interval IOA  An interobserver agreement index based only on the intervals in which either observer recorded the occurrence of behaviour; 
Scored IOA
calculated by dividing the number of intervals in which the two observers agreed that the behaviour occurred by the number of intervals in which either or both observers recorded the occurrence of the behaviour and multipying by 100. 

Scored IOA
ScoredInterval IOA is recommended as a measure of agreement for behaviours that occur at low rates because it ignores the intervals in which agreement by chance is highly likely. 

Unscoredinterval IOA  An interobserver agreement index based only on the intervals in which either observer recorded the nonoccurrence of the behaviour; 
calculated by dividing the number of intervals in which the two observers agreed that the behaviour did not occur by the number of intervals in which either or both observers recorded the nonoccurrence of the behaviour and multiplying by 100.  
Unscoredinterval IOA is recommended as a measure of agreement that occurs at high rates because it ignores the intervals in which agreement by chance is highly likely  
Trialby Trial IOA  An IOA index for discrete trial data based on comparing the observers' counts (0 or 1) on a trial by trial or item by item basis; yields a more conservative and meaningful index of IOA for discrete trial data than does total count IOA 
Total Count IOA  The simplest indicator of IOA for event recording data; based on comparing the total count recorded by each observer per measurement period; calculated by dividing the smaller of the two observers' counts by the larger count and multiplying by 100 