Stats And Mechanics Chapter 2 Flashcards
What is a measure of central tendency
A number we can use to to represent what is going on in the centre of our data
What are the three measures of central tendency
Mode (modal value( most frequent value/class)
Median(value in the ‘centre’ when the data is ordered)
Mean x - (x bar) = (sum of data values) / (number of data values)
If the data is in groups then the mean equation will be - (x bar) = (sum of fx) / (sum of f)
Where f is frequency and x is midpoint
Equation to find the position of the medan within grouped data
E.g. number of items = 70
Then position of Median = (70+1) / 2 = 35.5th
What is central tendency
Measure of location, measures the central location
How do you find the position of a quartile or percentile
Do quartile/percentile x number of data values
E.g. 17 -> Q3 -> 13th value
(3/4) x 17 = 12.75 (not a whole number so round up)
If the value is a whole number, the position would be between this number and the next
What are variance and standard deviation examples of
Measured of spread
They can be used to compare the spreads of two sets of data
What is the equation for variance
Sigma² = (sum of all data)² / (number of data items) - ( (sum of all data) / (number of data items) )²
If its for a table then the equation will be
(Sum of fx)² / (sum of f) - ( (sum of fx) / sum of f) )² for tables
What is the equation for standard deviation
Sigma = all rooted (sum of x)² / (number of data items) - ( (sum of x) / (number of data items) )
If in table include the frequency before x and replace n with sum of f
Equation to work out the IQR
Q3 - Q1
Equation to work out the inter percentile range
Pa - Pb (Normally P90 - P10)
What is coding
A way of making the calculations vor the mean and standard deviation easier
The formula is y = (x - a) / b
Y is coded data
X is original data
