Scatter Diagrams And Correlation (4) Flashcards
What is association
Two variables with a relationship between them
What data do scatter diagrams show
Bivariate data
Where do you plot the independent variable
On the horizontal x axis
What does the independent variable show
It shows the value you change
Where do you plot the dependent variable
On the y axis
What does the dependent variable show
The value you do not change
It depends on the explanatory variable
What is correlation
The link between two variables that shows a trend
What is positive correlation
When one variable increases another increases
What is negative correlation
When one increases the other decreases
What is linear correlation
When they lie on a straight line
(This can be positive or negative)
What is non linear correlation
Correlation that shows a curved line
What is a causal relationship
When a change in one variable directly causes a change in another variable.
E.g. The larger a fuel tank the more fuel a car uses
Does correlation directly imply causation
No
Correlation doesn’t always mean there is a causal relationship.
How many factors will cause a change in variables
Multiple.
Although a single scatter graph will show how one factor effects another there may be multiple
What is a line of best fit
A straight line drawn so the plotted points on a scatter diagram are evenly scattered either side of the line
What is a mean point used for
Drawing a more accurate line of best fit (than by eye)
How do you calculate the mean point
The mean x value and mean y value
What is interpolation
Using the line best fit within the given data values to estimate a value
What is extrapolation
Extending the line of best fit further than the given values, to estimate a data value
How reliable is interpolation or extrapolation
Interpolation - reliable as its within the known data values
Extrapolation - unreliable as it is past the known data values
What is the equation for a line / line of best fit
Y = mx + c
In statistics you are likely to see
Y = ax + b
A = gradient
B = y intercept
What is the line of best fit also called
The regression line
What does the line of best fit of a gradient show
The rate of increase of the dependent variable (response variable) to the independent (explanatory) variable
What does the y intercept show
The response variables value when the explanatory variable is 0
