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At the Centre for Education Statistics and Evaluation we are very keen to provide teachers and school leaders with the tools they need to scrutinise the various types of professional learning available. Please use our glossary of terms to better understand our meanings for some of the terms used throughout the Professional Learning Clearinghouse.



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Baseline – Initial collection of data which serves as a basis for comparison with subsequently acquired data.

Bias (statistics) – A systematic distortion of results away from the true value.



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Causal – Evidence that an effect is the direct consequence of an intervention.

Confidence interval – A range within which the true effect probably lies.

Control group – The group of subjects in a study that does not receive the intervention.
- For example: a group of students whose teacher does not participate in the professional development that is being evaluated.

Correlation – A measure of the strength of the relationship between two variables (expressed as a number). A correlation between two variables does not necessarily imply that one causes the other.
- For example: the strength of the relationship between attendance at school and achievement.



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Data – Measurements or observations that are collected as a source of information.
Dataset – A collection of observations.
Design – The method by which intervention and control groups are determined.



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Effect – A difference in the value of one variable (often an outcome you are interested in) that is associated with a change in one or more other variables.
Effect-size – A commonly-used measure of the strength of a phenomenon.
- For example: the degree of change in an average student’s performance in response to an intervention.
Empirical evidence – Knowledge acquired by observation or experiment.
Evidence base – Collection of robust information and data available on a topic.
Evidence-based practice – Teaching strategies and behaviours that are based on and backed up by the best available evidence.
Evidence hierarchy – A tool to classify evidence according to its quality.
Expert opinion – The views of a person generally considered to be very knowledgeable in a particular field.
External validity – The extent to which the results of a study are transferable to other students, other schools, or other countries.



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Gold standard – The highest level of quality on our evidence hierarchy.
Great Teaching, Inspired Learning (GTIL) – A NSW government reform designed to improve student outcomes through an improvement in teaching.



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Hierarchy of evidence – see evidence hierarchy.



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Internal validity – The rigour with which a study is conducted, and the extent to which the designers of a study have taken into account alternative explanations for any causal relationships they explore.
Intervention – A program, product, practice, or policy aimed at improving outcomes.
Intervention group – The group of subjects in a study that receives special treatment.
- For example: a group of students whose teacher participates in the professional development.



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Meta-analysis – A method of comparing and combining results of many other studies.
Metadata – The information that defines and describes data.
- For example: the definition and description of a population, the source of the data, or the methodology used in a study.
Methodology – The way in which a study has been designed.



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Negative effects – Evidence that an intervention harmed participants’ outcomes relative to doing nothing.



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Observation – The unit that is being examined in the study.
- For example: students, schools or classes. A study examining students might note that N=300. This means there were 300 students in the study.
Other evidence – The lowest level of quality on our evidence hierarchy.



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Population – A complete group with at least one characteristic in common.
Positive effects – Evidence that an intervention improved participants’ outcomes relative to doing nothing.
Pre-post comparison – Differences between the performances of an intervention group before and after the intervention takes place.
Professional development – Activities that develop an individual’s skills, knowledge, expertise and other characteristics as a teacher.
Professional learning – Changes in thinking, knowledge, skills and approaches to instruction that form practicing teachers’ or administrators’ repertoires.



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Quasi-experiment – A study that compares the outcomes of an intervention group with the outcomes of a control group that has not been chosen through randomisation.
- For example: a comparison of students in an intervention group at one school with a control group comprising students in neighbouring schools who have similar demographic characteristics (e.g. age, gender, race, socioeconomic status) and educational achievement levels.



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Randomised controlled trial (RCT) – A study that measures the effect of an intervention by randomly assigning individuals to an intervention group or a control group and then compares the achievement of the groups over time. These are widely considered to be the gold standard of evidence.
Reliability – The extent to which an experiment, test, or any measuring procedure yields the same result on repeated trials.



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Sample – A subset of a larger group.
Selection – The method that is used to decide which people in the population will be included in the study.
Selection bias – Error that can arise when allocating individuals to control and intervention groups.
Silver standard – Middle level of quality on our evidence hierarchy.
Standard deviation – A measure of variation across observations in a sample.
Statistical significance – A finding that the results are likely to be due to a real difference rather than chance.
Synthesis – A summary of many other studies.



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Treatment group – See intervention group.
True value – The value that is obtained if a study has been conducted without any errors or biases.



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Validity – The degree to which a study accurately reflects or assesses the specific concept that the researcher is attempting to measure.
Variable – A characteristic, number, or quantity that can be measured or counted.