Descriptive Statistics 2 Flashcards
What is skewness?
Asymmetry
What is positive skewness?
When the data ‘skews’ out to the right
What is negative skewness?
When the data ‘skews’ out to the left.
What is kurtosis?
‘pointiness’
What is the R function to get lots of descriptive stats?
describe()
If kurtosis is greater than 0 it means that
The graph is too pointy (focused around the center)
compared to normal
If kurtosis is less than 0 it means that
The graph is ‘too flat’ (compared to normal)
What does Tukey’s ‘five number summary’ consist of?
Minimum value (0th percentile)
25% percentile
Median (50th percentile)
75th percentile
Maximum (100th percentile)
A boxplot shows everything that is a part of?
Tukey’s five number summary
What do scatter plots do?
Show the relationship between numeric variables
(plot one variable on x-axis, plot two on y-axis)
What is a positive relationship?
What does a positive relationship look like in a scatter plot?
When one variable goes up, the other goes up too.
looks like going up a hill.
What is a negative relationship?
What does it look like in a scatterplot?
When one variable goes up, the other goes down.
looks like going down a hill
What does a strong correlational relationship tell us?
If we know the value of one variable it tells you a lot about the other one.
What does a weak correlational relationship tell us?
If we know the value of one variable it tells us very little about the other variable.
How do you make a scatter plot using R?
plot (x, y)
What is a Pearson’s correlation?
Measures the strength and direction of a relationship.
It assumes the relationship is linear.
Can Pearson’s work with non-linear correlations?
No
How do you do a Pearson’s correlational analysis in R?
cor.test(x, y)
What do you use Spearman correlations (Spearman’s Rho) for?
To measure non-linear relationships.
In statistics, ρ refers to?
Spearman’s rho
What are the characteristics of Spearman’s correlation?
It’s a number from -1 (perfect negative) to 1 (perfect positive)
It doesn’t assume the relationship is linear
All it assumes is monotonicity
A curve is monotonic when?
If it always goes up or always goes down.
(Doesn’t have to be linear though)
A curve is non-monotonic when?
It goes up and down at certain points.
How do you do a correlational analysis in R?
library(lsr)
correlate()
