# Statistics Key Terms

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Continuous data
Data that can take any value on a continuous numerical scale.
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Discrete data
Data that can only take particular values on a continuous numerical scale.
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Bivariate data
Pairs of related variables.
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Census
A set of data that contains information about every member of a population.
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Sample
A set of data that contains information about part of a population.
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Sampling units
People or items that are to be sampled.
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Sampling frame
A list of the people or items that are to be sampled.
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Random sample
A sample that is chosen without a conscious decision.
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Stratified sample
A type of sampling where the population is split into strata that have something in common. A random sample is taken from each stratum, in proportion to the size of each statum.
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Systematic sampling
From the sampling frame, a starting point is chosen at random. Items are then chosen at regular intervals.
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Primary data
Data that is collected by the person who is going to use them.
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Secondary data
Data that has been collected by somebody else.
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Survey
The collection of data from a given population that is used to analyse a particular issue.
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Pilot survey
A small scale survey that is used to test the design and methods of a particular survey
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Questionnaire
A set of questions designed to obtain data.
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Open question
A question that suggests no answers.
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Closed question
A question that has a set of answers for the respondent to choose from.
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Class
A group used to distinguish data if it is widely sppread
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Database
An organised collection of information.
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Cumulative frequency
A running total of frequencies
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Histogram
A type of graph that show a set of data is distributed across the class intervals.
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Frequency density
The height of a bar in a histogram. It is calculated by dividing the frequency by the class width.
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Positive skewness
Where data is more concentrated towards the right hand side of a graph. The median is closer to the upper quartile.
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Negative skewness
Where data is more concentrated towards the left hand side of a graph. The median is closer to the lower quartile.
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Mode
The value that occurs most often.
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Median
The middle number in an ordered list. It can be calculated by 1/2(n+1)
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Mean
Adding up the numbers and then dividing by how many there are.
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Modal class
The class with the highest frequency.
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Range
Where the smallest value is subtracted from the largest value.
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Lower quartile
A value that splits the lower 25% of the data. Calculated by 1/4(n+1)
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Upper quartile
A value that splits the upper 25% of the data. Calculated by 3/4(n+1)
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Interquartile range
The upper quartile - the lower quartile. Sometimes shortened to 'IQR'
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Box plot
A type of graph that can display the maximum value, the minimum value, the median, the upper quartile and the lower quartile.
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Outiler
Any value that is 1.5x the IQR below the lower quartile or 1.5x the IQR above the upper quartile.
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Variance
A measure of dispersion or spread.
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Standard deviation
A measure of the dispersion of a set of data from its mean. The more spread apart the data, the higher the deviation. It is calculated as the square root of the variance.
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Correlation
A measure of the strength of the linear association between two variables.
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Negative correlation
When one variable decreases as the other increases.
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Positive correlation
When one variable increases as the other decreases.
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Causal relationship
When a change in one variable directly causes a change in another variable.
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Interpolation
When the data point that you need lies within the range of given values.
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Extrapolation
When the data point you need lies outside of the range of given values.
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Spearman's rank
A numerical measure of the correlation between two sets of data. It tells us how close the agreement is.
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General trend
The way that the data changes over time.
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Trend line
Line that shows the general trend of the data.
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Seasonal variation
A pattern that repeats. It is calculated by the actual value - the trend value.
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Moving average
An average worked out for a given number of successive observations. They are plotted at the mid-point of the time intervals they cover.
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Trial
An act of testing / doing something.
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Outcomes
The possible results of a trial.
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Event
A set of one or more successful outcomes
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Probability
A numerical measure of the chance of an event happening. Calculated by the number of successful outcomes divided by the total number of possible outcomes.
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Simulation
The imitation of the conditions of a situation by a theoretical study.
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Sample space
A list of all possible outcomes.
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Mutually exclusive
Where outcomes or events cannot happen at the same time.
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Exhaustive
Where a set of events contains all possible outcomes.
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Independent
Where the outcome of one event does not affect the outcome of the other event.
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Conditional probability
The probability of 'A' given that 'B' has already happened.
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Probability distribution
A list of all possiblle outcomes together with their probabilities.
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Discrete uniform
A type of distribution where each outcome is equally likely.
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Binominal
A type of distribution which has a fixed number of independent trials. Each trial has only two outcomes: success (p) or failure (q).
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Normal
A type of distribution that has an equal mode, median and mean. It is symmetrical about the mean.
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Control chart
A time series chart that is used for process control.
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Warning limit
A limit set at two standard deviations from the mean. (95% of data lies within 2 s.d.)
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Action limit
A limit set at three standard deviations from the mean. (99.8% of data lies within three s.d.)
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## Other cards in this set

### Card 2

#### Front

Data that can only take particular values on a continuous numerical scale.

Discrete data

### Card 3

#### Front

Pairs of related variables.

#### Back ### Card 4

#### Front

A set of data that contains information about every member of a population.

#### Back ### Card 5

#### Front

A set of data that contains information about part of a population.

#### Back 