Data Processing, Presentation and Interpretation Key Terms
Variable: A value that varies
Random variable: A value that varies randomly
Frequency: The number of times a value occurs in a data set
Categorical data: Data in categories (also known as qualitative data)
Numerical data: Data defined in some way by numbers
Ranked data: Ordered data - Data given by their position in a group rather than by
measurements or scores
- Median: Value in the middle of the data set (for n times, median = (n+1)/2 th item).
Resistant to outliers
- Lower quartile: Value in the middle of the start and middle values
- Upper quartile: Value in the middle of middle and end values
- Interquartile range: Difference between upper and lower quartile
- Range: difference between highest and lowest value
- Semi interquartile range: Half the interquartile range
- Box plot and cumulative frequency: Used to display ranked data
Discrete variables: They can take certain particular values but not those in between
Continuous variables: They can take any particular value. You cannot list all the possible
values
Distribution: The pattern in which data is displayed or occurs
Unimodal: If there is one peak in the distribution
Bimodal: When there are two peaks in the distribution
Positive skew: When the distribution is skewed to the left (smaller values of ‘x’)
Negative skew: When the distribution is skewed to the right (larger values or ‘x’)
Grouped data: When there are many possible values for a variable, it is convenient to
allocate the data to groups
- Grouped frequency table: When individual values are not known and instead of
discrete values for the variable, there is a group the value can be put in (I.e. 0-9,
10-19, 20-29, etc for ages)
Ungrouped data: Data that is first gathered from experiments or studies, the data is raw, not
categorised, classified or otherwise sorted or grouped.
Bivariate data: When there are two variables attached to each item
Multivariate data: When there are more than two variables attached to each item
Ways of presenting categorical data: pictograms, bar charts, dot plots and pie charts
Modal class: The class with the highest frequency
Central tendency:
1. Mode: The value that occurs most commonly in a data set
2. Median: Covered above
3. Mean:
- Arithmetic: Found by adding the individual values together and dividing by
the number of values added
- Weighted mean: When the sum of the frequencies multiplied by the value of
the variable is divided by the sum of the frequencies (sigma fx / sigma f)
4. Mid range: The mean of the maximum and minimum value
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