AQA GCSE Statistics key terms

The intended value for the measurement or statistic being monitored.

The group in an experiment that receives the treatment being investigated.

The probability calculated from a mathematical model rather than observed results. For a fair coin, the theoretical probability of heads is $\frac{1}{2}$.

An additional variable that may influence both variables being studied, helping to explain their correlation.

A set of observations recorded in time order, such as monthly sales figures.

A graph showing observations in time order, with time on the horizontal axis.

A mistake made when copying or entering data, such as typing an extra digit.

A branching diagram showing possible sequences of outcomes and, when labelled, their probabilities.

The general direction of change in data over time: rising, falling or approximately level.

A line on a time series graph representing the general direction of the data over time.

One repetition of a probability experiment, such as tossing a coin once.

An axis with part of its range omitted, often because it starts above zero.

A table that classifies data by two characteristics, with one shown in the rows and the other in the columns.

Data presented without combining different values into broader classes or intervals; individual recorded values remain identifiable.

The members belonging to either set or both. $A\cup B$ means ‘A or B, including both’.

The value approximately three-quarters of the way through ordered data, with about 75% of values below it.

An observation that genuinely represents what was being measured, even if it is unusual.

The extent to which a statistical method supports a sound conclusion; capture–recapture depends on its assumptions being reasonable.

A characteristic or quantity that can take different values for different people or items.

A measure of spread equal to the square of the standard deviation: $\sigma^2$.

A diagram using overlapping closed curves inside a rectangle to show membership of sets and their relationships.

A graph using separate vertical lines to show the frequencies of discrete numerical outcomes.

A graphical representation of data, such as a bar chart or scatter graph.

A horizontal control-chart line marking a limit beyond which another sample should be taken immediately. For a sample-mean chart, warning limits are $\mu \pm 2\sigma$, where $\sigma$ is the standard deviation of the sample means.

A relationship with a recognisable trend but more widely scattered points. AQA classifies coefficients from $0.2$ up to but not including $0.6$, or from $-0.2$ down to but not including $-0.6$, as weak.

A number determining how strongly a value contributes to a calculation, such as the number of items bought.

An index that combines values using weights to reflect their relative importance.