Averages And Spread Flashcards
What is an average also called?
Measure of central tendency
What is x̄?
The mean (x bar)
What is it called when you have two modes?
Bimodal
What is Q1?
The lower quartile
What is Q2?
The median
What is Q3?
Upper quartile
What is the median?
The middle value when the data is in order.
What is the lower quartile?
One quarter of the way through a data set.
What is the upper quartile?
Three quarters of the way through the data set.
What is a measure of spread?
A measure of how spread out the data is.
eg range, IQRange
What is the advantage and disadvantage of using the range as a measure of spread?
Takes all the data into account but can be affected by extreme values.
What is the advantage of using the interquartile range as a measure of spread?
It’s not affected by extreme values but only considers the spread of the middle 50% of the data.
What is standard deviation (σ) equal to?
The square root of variance
What do standard deviation and variance show?
The dispersion of values around the mean. Standard deviation gives a kind of ‘average’ amount by which all the values deviate from the mean.
What is the best measure of spread?
Standard deviation / variance.
What does Σx mean?
Sum of the x values.
What does Σx^2 mean?
Sum of the x^2 values.
What does σ^2 x mean?
Variance
What does σx mean?
Standard deviation
What does n mean?
Number in data set.
What does min(x) mean?
Smallest data value
What does max(x) mean?
Largest data value
What is an outlier?
An extreme value that lies outside the overall pattern of data.
What is a common definition of an outlier?
• Greater than Q3 + k(Q3 -Q1)
Or
• Less than Q1 - k(Q3 - Q1)
What is (Q3 - Q1)?
The interquartile range.
Are there sometimes outliers that are legitimate values?
Yes
When outliers are a mistake, what are they called?
Anomalies
What is the process of removing anomalies from a data set known as?
Cleaning the data.
What must you do when removing anomalies?
Justify why it is an anomalie and not just an outlier.
What does a box plot show?
•median
•quartile
• max and min values
•outliers
When comparing 2 box plots what should you consider?
• median as a measure of average
• IQR as a measure of spread
• outliers
• symmetry
What is a symmetrical box plot?
When the median is in the middle of the box, there is no skew.
Q3 - Q2 = Q2 - Q1
What is a positive skew box plot?
When the median is to the left of the box.
Q3 - Q2 > Q2 - Q1
What is a negative skew box blot?
When the median is to the right of the box.
O3 - Q2 < Q2 - Q1
In a histogram, what is the area of the bar proportional to?
The frequency in each class.
