Averages And Measures Of Spread Flashcards
What is a median
Middle observation in set of ordered data
What is a mode
Most frequently occurring numbers
How do you calculate the median
N+1 divided by 2
This number along in the list
What is a positive and negative skew
Positive = curve peaks left of the middle
Positive = mean greater that median
What is a normal distribution
Mean and median approx equal
What should you do if both variables are categorical
Use a contingency table
What is a percentile
Value at or below which a specified percentage of the scores in the distribution fall
How do you calculate percentiles
Percentile / 100
X n+1
(N is number of digits in data set)
This answer, this number in array
What is a quintile
5 equal groups that the population can be divided into (20%s)
What is a tertile
Thirds
What is the range
Difference between highest and lowest values
What is the interquartile range
Difference between upper and lower quartile
What is the sd
Measures average deviation from the mean
What is variance
SD squared
What is a box plot
Graph of median, inter quartile range and outliers
When is SD used
When the mean is a good measure of average
What do larger/ smaller SDs mean
Larger - more spread from mean
When is sd used
When the data is not too skewed or when mean is being used as measure of average
What is a residual
Difference between particular observation and the mean
What happens if we add or subtract by a constant number in a data set
Changes the mean by the amount added or subtracted
SD remains the same
What is the variance
Standard deviation squared
What happens when you multiply or divide by a constant
Changes mean by an amount equal to multiplying or dividing by the mean
Does the same to SD
What happens to range if distribution when you multiply or divide by a constant
Shrink if less than 1, decreased range
Increase if constant more than 1, increased range
What is it called when the observations have been converted into z scores
Standardised data
What is the z score equation
Z = observation - mean / SD
What do positive and negative z scores mean
Positive = above the mean
Negative = below the mean
What does a Z score measure
The number of standard deviations an observation is from the mean
What does the mean of the z scores always equal
0
What does the sd of all the z scores always equal
1
What are z scores used for
To rank data
Can create ranking scales on several variables
Can then compare z scores for these indicators by creating an index of all variables
