Regression

Statistics — Third Secondary

Common mistakes

Comparison aspect	Main idea	Keywords
Confusing b and a	b is the slope and a is the intercept on the y-axis. Calculate b before a	slopeinterceptaxisCalculate
Forgetting the negative sign	when the correlation is negative the slope is negative as in b = −1.7 in Example 4	correlationslopeExample
Calculating a without the means	the intercept is always found by a = ȳ − b x̄ not by guessing	interceptalwaysfoundguessing
Assuming the line works for every value	predictions outside the data range may give unrealistic results	predictionsoutsidedatarange
Using the equation of y on x to predict x	the equation of y on x is used only to predict the value of y	usedvalue

Regression · 6 / 7