The number of points on the graph tells us the number of subjects. It is good to remember that the points on scatter graphs represent subjects. On a graph one axis will be labelled as ‘number of TVs sold’, and the other as ‘amount of money spent on advertising’ and then each cross will indicate each year. For each year the number of TV sales and money spent on advertising has been recorded. However, you must remember that bivariate data has a subject and two variables are recorded for each subject. As the table has 3 rows of data it may appear to have 3 variables. They have recorded the year, the number of TVs sold, and the amount of money spent on advertising. ![]() For example, the table below shows information from a small independent electronics shop. Sometimes bivariate data can appear to have 3 variables and not just two. In the same way you cannot say that higher ice cream sales cause hotter temperatures. However, there is not sufficient evidence for you to make this assumption both scientifically and statistically. It might then be tempting to say that this indicates that hot weather causes higher ice cream sales. You can describe the relationship as the hotter the temperature, the greater the number of ice-creams sold. In other words, a relationship between two variables does not indicate that one variable causes another.įor example, you may find a positive correlation between temperature and the number of ice-creams sold. When interpreting scatter graphs, it is important to know that correlation does not indicate causation. Place an x at this point (5,1200).Ĭontinuing this method, we get the following scatter graph: To plot the coordinate for Car 1, we locate 5 on the horizontal axis (Age = 5 ), and then travel vertically along that line until we locate £1200 on the vertical axis (Selling price = £1200 ). Make sure you give your graph a suitable title. Plot each car as a cross on the graph one at a time. This will require drawing a break in the scale from the origin to 800. A sensible scale would be 800 to 2200 in steps of 100. This variable has the lowest value of 850 and highest value of 2200. Construct a best-fit line for the data on the plot below for the Hawaiian hotspot. One way to determine average plate motions is to use the trend of the data. location relative to Kilauea (the present active volcano). The other axis will show the selling price of the car. The graph below shows a plot of the age of volcanoes vs. A sensible scale would be 0 to 10 going up in unit steps. ![]() This variable has the lowest value of 2 and highest of 10. Two pieces of data have been recorded for each car, age and selling price.Įach axis should have one of the variables and the scale should be appropriate for the given values. In this question the subjects are the ten cars.
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