Week 1: Data Visualisation and Descriptive Stats Flashcards
Interquartile Range
the difference between the upper quartile and the lower quartile
How to find the mean from a histogram?
weighted mean as all observations are added up and divided by the total number of observations
Drawbacks of Mean as descriptive stats
sensitive to outliers – the effect of the inclusion of one piece of data can have a significant effect on the result
Interpolation method to find median
Endpoint of previous class + (class width x number of remaining observations/class frequency)
What is the skewness of data when Mean > Median
positively-skewed distribution (skewed to the right)
What does it mean in terms of skewness when Mean < Median
negatively skewed distribution (skewed to the left)
What does it look like graphically when data is positively skewed?
long tail heading towards increasingly +ve values on the x-axis
What does it look like graphically when data is negatively skewed?
long tail heading towards increasingly -ve values
Interquartile Range (IQR)
IQR = Q3 – Q1
Boxplot - what do the following represent? Middle line, upper end, lower end, whistkers
Middle line = median
Upper end = upper quartile
Lower end = lower quartile
Whiskers drawn from the quartiles to the observations furthest from the median but not by more than one and half times the IQR – whiskers terminated by horizontal lines
How do you calculate upper whisker? Boxplots
(Xn Q3 – 1.5 x IQR)
How do you calculate lower whisker? Boxplots
(X(1) Q1 – 1.5 x IQR)
Sample variance equation
Sample Standard Deviation Equation
