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Data and Society 9-12 / Week 09 / Thursday
4/6
Week 09 · Finding the Middle and the Pattern

Thursday

Patterns and causes
// Typical values, extreme values and what a pattern can prove
⏱ about 20 min

Thursday: Patterns and Causes

Comet has plotted six Saturdays on graph paper. Each dot shows how many workshops ran and how many people came through the door.

"Look!" she says. "More workshops, more people. Workshops bring in members. Let's run ten every Saturday!"

Wren studies the dots. They climb from left to right. "What do you notice? The pattern is real."

"But does the chart show why?" he asks.

Keeper Ines flips through her desk notes. "Two of those busy Saturdays were also street fair days in town."

Nova hovers between the graph and the notes. "Would you like a hint?" she asks. "A pattern can have more than one possible reason. How could you check?"

A pattern in two variables

Made-up SaturdayWorkshops that dayPeople through the door
Saturday 1064
Saturday 2170
Saturday 3281
Saturday 4395
Saturday 54102
Saturday 65110

Made-up data from the Commons Count story. Saturday 4 is the door count day from week 4.

An X-Y plot shows whether two things are related. If both increase at the same time, the relationship is positive.

Workshops are planned ahead, so the door count cannot change them. Workshops are the independent variable here. The door count is the dependent variable.

READ THE PLOT
  • Read the question.
  • Tap your answer.
What kind of relationship do the dots show?
How many more people came on the 5-workshop Saturday than on the 0-workshop Saturday?
Which variable depends on the other?

Correlation is not cause

Data may show a correlation, a pattern where two variables change together.

A correlation does not prove that one thing causes the other.

More research is needed to learn how the two are related.

Often one source does not hold all the data needed. You may need to combine sources before you conclude.

StatementTrue or false?
The dots show a positive relationship.?
The plot proves that workshops cause more people to come.?
Keeper Ines's notes are a second source the crew can combine with the plot.?
More research is needed to learn why the two variables move together.?
WHY THIS EXERCISESeparating a pattern from its cause keeps the crew from acting on a guess.
When two variables rise together, the relationship is ____.
A pattern where two variables change together is a ____.
FROM A PATTERN TO A CAREFUL CONCLUSION
  • ?Plot the two variables and look for a pattern.
  • ?Name the relationship: positive, negative or none.
  • ?Combine another source to test those explanations.
  • ?Write a conclusion that says what the data can and cannot show.
  • ?List other things that could explain the pattern.
WHY THIS EXERCISEThis order turns an exciting pattern into a claim the crew can defend.
On graph paper, make an X-Y plot of the six Saturdays. Put workshops on the x-axis and people on the y-axis, starting at 0.

Careful thinking, data analyst. Tomorrow is Impact Friday: the median goes to work far beyond the Commons.

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