L2 - Descriptive Statistics Flashcards
What is categorical (qualitative) data?
Typically non-numerical data that can be sorted into defined categories e.g. Gender or Nationality
What are the two types of numerical (quantitative) data? Define.
Discrete - Counted items e.g. number of children
Continuous - Measured characteristics, can be infinitely precise e.g. weight
What are the four ‘levels of measurement’?
Nominal Data, Ordinal Data, Interval Data, Ratio Data
What is nominal data?
Categorical, unrankable data e.g. marital status (you can be married or unmarried, but you can’t be ‘more married’)
What is ordinal data?
Categorical data that can be ranked - e.g. grades
What is interval and ratio data? What is the difference?
Where data is quantitative and inferences can be made based on differences e.g. you can find the average.
Difference is that with ratio data there is a true zero e.g. Kelvin is ratio data because 0K means no heat, Celcius is not.
What are the three measures of central tendency?
Mean, Median and Average
What are the three measures of variance?
Range, Variance and Standard Deviation
What are the disadvantages of the mean?
Affected by extreme values (outliers)
How do you find the median if the data set is even?
Find the average of the two middle numbers e.g. the median of 1,2,3,4 would be 2.5
What are the disadvantages of range?
It ignores the way data are distributed, with outliers have a massive impact.
What is variance? How do you calculate it?
A measure of the deviation of each value from the mean.
Calculated by squaring the difference for each value, squaring it, then finding the average for all the results
What is standard deviation? Why does it involve finding the square root?
The square root of the Variance i.e. the average difference of each value, squared, from the mean.
Because it allows Std Dev. to be expressed in the same units.
What are the advantages of standard deviation and variance?
Each value in the data set is used
Values farther from the mean are given additional weight because they are squared.
What is the coefficient of variation?
Variation expressed as a percentage by dividing the standard deviation by the mean?
