Bivariate Data

Bivariate data Sets of data represented by two variables. Eg. no. of electrical appliances vs Cost of electricity bill. Independent variable – no. of appliances Dependent variable – electricity bill

For each of the following, state the independent and dependent variables. 1. House prices and the no. of bedrooms in those houses 2. Gelato sales and the temperature 3. No. of hours spent studying for a Mathematics test and the score on that test.

Scatter plots - Used to display bivariate data Dependent variable Independent variable

Example

correlation Form – linear or non-linear Direction – positive or negative Strength – strong, moderate or weak Linear Non- linear

Positive Negative

Draw a scatterplot for the following data. Max temp 20 22 24 25 26 28 30 31 Gelato sales 165 180 200 223 250 271 285 300 Describe the correlation between the two variables. Linear or non-linear? Positive or negative? Strength? Make conclusions about the relationship between temperature and gelato sales.

Confidence Predicted values are only indications of what might happen Interpolation – prediction within range of points. More confidence. Extrapolation – prediction outside range of points. Less confidence.