GCSE Statistics vocabulary

Hypothesis
- A statement which may or may not be true.
- A statistical investigation is used to see if there is evidence to support the hypothesis.
Population
- All items/people being investigated (e.g. all students in Year 10, all fireworks made by a factory).
Sample Frame
- A list of all members of the population (could be a register or database).

Random Sample
- All items in the population have an equal chance of being selected for the sample.
Stratified (Random) Sampling
- Population divided into strata (e.g. gender/school year), matching sample proportions to the population.
- Members are chosen randomly from each strata.
Judgment Sampling
- Non-random sampling, selecting using specific criteria (e.g. first 20 items/people).
Cluster Sampling
- Non-random sampling using all members from randomly chosen clusters (e.g. all pupils in 3 randomly chosen tutor groups).
Quota Sampling
- Non-random sampling where an interviewer selects a pre-determined number of people from different age-groups/genders.
Systematic Sampling
- Non-random sampling from a random start point at fixed intervals.

Cleaning Data
- Improving reliability and usability of data for statistical software.
- May involve dealing with outliers, missing data, and standardizing formats/units.
Anomaly
- A value that does not fit the rest of the data (e.g. far from the line of best fit).
Outlier
- A suspiciously high or low value.

Variables
- Values being investigated that vary among members of the population; can be discrete, continuous, qualitative, etc.
Multivariate Problems
- Investigating more than one linked variable (e.g. driving test performance by gender and time of day).
Categorical Data
- Data that fits into clearly defined categories (e.g. gender, voting intention).
Ordinal Data
- Data indicating a rank order (e.g. positions in a race).

Distribution
- The set of values and their frequencies or probabilities.
Extraneous Variables
- Variables not being investigated that affect outcome (e.g. time of day when comparing reaction times).

Control Group
- Used alongside a test group for comparison.
Matched Pairs
- Used to make two groups as similar as possible, reducing extraneous variable effects.

Closed Questions
- Require a choice from stated answers (easy to analyze and graph).
Open Questions
- Have no restrictions on answers (harder to analyze, often best avoided).
Pilot Survey / Pre-Test
- Testing a questionnaire on a small scale to check for necessary changes.

Used to estimate responses to sensitive questions for reliability by adding an element of chance (e.g. using dice).

Reliability
- The extent to which repeating a process leads to similar results.
Validity
- The extent to which a process measures what it intends to.

Choropleth Map
- Uses shading; darker represents higher numbers.
Central Tendency
- Means average (e.g. mean, median, mode).
Dispersion
- Measures spread (e.g. range, IQR, standard deviation, variance).
Variance
- The square of the standard deviation.

Trend
- Long-term changes over time; described as rising, falling, or level.
Seasonal Variation
- Patterns that repeat at regular intervals.
Mean Seasonal Effect
- The average of numerical differences from the trend line for a certain time.

Index Number
- New value as a percentage of the value in a base year; stated without “%.”
RPI / CPI
- Retail Price Index / Consumer Price Index, measures of inflation.
GDP
- Gross Domestic Product indicating total value of goods and services produced by a country.
Standardised Rates
Adjusts rates for age distribution comparisons.

Sample Space Diagram
- Represents all possible outcomes (e.g. table for dice rolls).
Mutually Exclusive Events
- Events that cannot happen together (P(A) + P(B) = P(A or B)).
Exhaustive Events
- All possible outcomes included; probabilities sum to 1.

B(n, p)
- Binomial distribution with n outcomes and probability p.
N(μ, σ²)
- Normal distribution with mean μ and standard deviation σ.
- Key properties include symmetry and peak at the mean.