A writer for the Big Think wrote about how "Butter supply and life-satisfaction are linked". It's a dairy interesting story with perfect scatterplots for practicing correlational designs.
Writer Frank Jacobs used the following bullet-points to open his story:
- Haiti and other countries with low butter supply report low life satisfaction.
- The reverse is true for countries such as Germany, which score high in both categories.
- As the graph below shows, a curious pattern emerges across the globe. But is it causation or correlation?
You should click on the story and scroll down to the first scatterplot.
a) What does one dot represent on this scatterplot?
b) What kind of correlation is being represented here: positive, negative, or zero?
c) Find your own home country. Is your country above the median or below the median on butter supply? Is your country above the median or below the median on life satisfaction?
d) What would happen to the scatterplot if it were drawn with butter supply on the y-axis and happiness on the x-axis? Would it have the same shape and slope?
The writer states:
Yet as the map shows, an abundance of butter does make people happy. Or could it be a case of correlation instead of causation? In that case, something else influences both life satisfaction and the availability of butter to go up and down together.
d) In the curious paragraph above, the writer makes a clear causal claim. What is it?
e) After making the causal claim, the writer backs off, stating that "something else" could be associated with both life satisfaction and the availability of butter. He's talking about third variables here–or internal validity. What possible third variables might plausibly be correlated with both butter supply and life satisfaction in the world's countries?
To help you consider possible third variables, zoom in on the countries that are in the lower left and upper right quadrants of the butter scatterplot. What dimension seems to separate the countries in those two quadrants?
f) Take a look back at the column in Big Think. Is this data (and scatterplot result) from a published, peer reviewed study in an empirical journal?
I butter thank Sue Frantz of Highline College for sharing this story with me.