![]() ![]() In a line chart, however, the same daily rainfall and particulate values are displayed as two separate data points, which are evenly distributed along the horizontal axis. These numbers represent the values in cell A9 and B9 on the worksheet. The first data point to appear in the scatter chart represents both a y value of 137 (particulate) and an x value of 1.9 (daily rainfall). These data points may be distributed evenly or unevenly across the horizontal axis, depending on the data. The chart displays points at the intersection of an x and y numerical value, combining these values into single data points. Often referred to as an xy chart, a scatter chart never displays categories on the horizontal axis.Ī scatter chart always has two value axes to show one set of numerical data along a horizontal (value) axis and another set of numerical values along a vertical (value) axis. In a scatter chart, the daily rainfall values from column A are displayed as x values on the horizontal (x) axis, and the particulate values from column B are displayed as values on the vertical (y) axis. For example, when you use the following worksheet data to create a scatter chart and a line chart, you can see that the data is distributed differently. Since 10mm is much higher than the highest rainfall recorded, we cannot assume that the line of best fit would still follow the pattern when the rainfall is 10mm, so the value of 64 umbrellas is not a reliable estimate.The main difference between scatter and line charts is the way they plot data on the horizontal axis. This process is called extrapolation, because the value we are using is outside the range of data used to draw the scatter graph. This gives a value of approximately 64 umbrellas sold. If there was 10mm of rainfall, we could extend the graph and the line of best fit to read off the number of umbrellas sold. Draw a line by going across from 3 mm and then down.Īn estimated 19 umbrellas would be sold if there was 3 mm of rainfall. The value of 3mm is within the range of data values that were used to draw the scatter graph.įind where 3 mm of rainfall is on the graph. To estimate the number sold for 3mm of rainfall, we use a process called interpolation. For example, how many umbrellas would be sold if there was 3mm of rainfall? What if there was 10mm of rainfall? The line of best fit for the scatter graph would look like this: Interpolation and extrapolationįrom the diagram above, we can estimate how many umbrellas would be sold for different amounts of rainfall. It should also follow the same steepness of the crosses. Lines of best fitĪ line of best fit is a sensible straight line that goes as centrally as possible through the coordinates plotted. No correlation means there is no connection between the two variables. Negative correlation means as one variable increases, the other variable decreases. Positive correlation means as one variable increases, so does the other variable. Graphs can either have positive correlation, negative correlation or no correlation. If data plotted on a scatter graph shows correlation, we cannot assume that the increase in one of the sets of data caused the increase or decrease in the other set of data – it might be coincidence or there may be some other cause that the two sets of data are related to. However, it is important to remember that correlation does not imply causation. On days with higher rainfall, there were a larger number of umbrellas sold. The graph shows that there is a positive correlation between the number of umbrellas sold and the amount of rainfall. The number of umbrellas sold and the amount of rainfall on 9 days is shown on the scatter graph and in the table. Scatter graphs are a good way of displaying two sets of data to see if there is a correlation, or connection. ![]()
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