A testable statement about the relationship (difference, association etc.) between two or more variables.
Bias
A systematic distortion.
Calculated value
The value of a test statistic calculated for a particular data set.
Calculated value
The value of a test statistic calculated for a particular data set.
Control
The extent to which any variable is held constant or regulated by a researcher.
Cost-benefit analysis
A systematic approach to estimating the negative and positive impact of any research.
Critical value
In an inferential test, the value of the test statistic that must be reached to show significance.
Critical value
In a statistical test the value of the test statistic that must be reached to show significance.
Degrees of freedom
The number of values that are free to vary given that the overall total values are known.
Effect size
A measure of the strength of the relationship between two variables.
Heuristic
A mental rule or short-cut allowing for more efficient decision making, but often leading to cognitive biases.
Levels of measurement
Refers to the different ways of measuring items or psychological variables; the lower levels are less precise.
Meta-analysis
A research method in which a researcher statistically analyses the findings of a number of different studies to investigate the overall effect.
One-tailed test
Form of test used with a directional hypothesis.
Open questions
Questions that invite respondents to provide their own answers. Tends to produce qualitative data.
Order effect
In a repeated measures design, an extraneous variable arising from the order in which conditions are presented, e.g. a practice effect or fatigue effect.
Order of magnitude
A means of comparing numbers by focussing on the overall size (magnitude). This may be done by expressing the number in standard form (powers of 10).
Pilot study
A small scale trial run of a study to test any aspects of the design, with a view to making improvements.
Population
The group of people that the researcher is interested in studying, from whom a sample is drawn, and about whom generalisations can be made.
Presumptive consent
A method of dealing with lack of informed consent or deception, by asking a group of people who are similar to the participants whether they would agree to take part in the study. If they consent, it is presumed that the real participants would also agree.
Probability (p)
A measure of the likelihood or chance that certain events will occur.
Probability (p)
A numerical measure of the likelihood or chance that certain events will occur. A statistical test gives the probability that a particular sample did not occur if the null hypothesis for the population was true, i.e. there was no real effect.
Random allocation
Allocating participants to experimental conditions or groups using random techniques.
Review
A consideration of a number of studies that have investigated the same topic in order to reach a general conclusion about a particular hypothesis.
Significant figures
The number of single digits (other than zero) used to represent a number. The zeros exist as place holders, to maintain the correct order of magnitude.
Standard form (or scientific notation)
A way of expressing any number in two parts, in the form A x 10n. A is a number between 1 and 10, and n can be positive (for very large numbers) or negative (for very small numbers).
Statistical test
Procedures for drawing logical conclusions (inferences) about the population from which samples are drawn.
Table of critical values
A table of numbers used to judge significance. The calculated value of the test statistic is compared to the relevant number in the table (the critical value) to see if the calculated value is significant.
Test statistic
The number calculated in statistical testing. For the sign test, the test statistic is known as S.
Test statistic
The name given to the value calculated using a statistical test. For each test this value has a specific name such as S for the sign test.
Two-tailed test
Form of test used with a non-directional hypothesis.
Two-tailed test
Form of test used with a non-directional hypothesis.
Volunteer bias
A form of sampling bias arising because volunteers have special characteristics such as higher than average motivation.