Lecture 16: Scatter Plots And Correlations Flashcards
(21 cards)
Scatterplots
A graph used to illustrate the relationship between two quantitative variables
Scatterplots measure the relationship between 2 ______ variables
Quantitative
Measurements in scatter plot samples come in _____
pairs (usually from the same subject)
Each point on the scatterplot graph represents a _______
subject
Correlation
A number between -1 and 1 indicating the strength of the linear relationship between two variables
The more nearly the points “line up” in the scatter plot, the _____ the correlation (in absolute value)
Larger
Zero correlation
No linear relationship
Positive correlation
Points lean to the right
When one variable’s value increases the other variable’s value increases
Negative correlation
Points lean to the left
When one variable’s value increases the other variable’s value decreases
Most common way to compute a correlation is using the ______ correlation
Pearson
The symbol for the population correlation is
p (rho)
The symbol for the sample correlation is
r (an estimate of p)
Does a correlation have units? If so what are they?
They have no units it’s a number silly
Will a correlation be affected by the multiplication/division/subtraction/addition of some constant value from all the measurements?
Nope it’s not affected by linearly rescaling the units eg. correlation between height and weight is same regardless of whether height is measured in inches or meters
The sample correlation is just an estimate of the ________ _______
population correlation
Where should we compute a CI?
Around the sample correlation (the estimate)
Could we conduct a p-value for a null hypothesis test?
Yes!
CI for population proportion/population correlation isn’t perfectly symmetric around the estimate due to the hard _____ and ______ on possible values, so unlikely when estimating a population mean, there won’t be exactly the same margin ____ the estimate as _____ the estimate
Floor
ceiling
(proportion must be between 0-1 and correlation must be between -1-1)
Above
Below
Correlation means Causation true or false?
FALSE
Why does correlation not equal causation
Some third variable could be the cause
If we need strong evidence of causation that calls for an ______, not a correlational study
Experiment! –> no confounding variables/limits them
