Correlation
Correlation is when two things change together in a pattern you can track and measure.
The more slices you take from a loaf of bread, the fewer slices remain. Track both numbers and they move together in a clear pattern. One goes up, the other goes down.
Explaining correlation by grade level
Think about Big Mac prices around the world. In rich countries, a Big Mac costs more. In poorer countries, it costs less. When one thing goes up and the other goes up too, they move together. That pattern is what we call correlation.
Projects that explore correlation
Graphs of individual years show no clear pattern in earthquake data — but when you group decades of records into 5-year, 10-year, and 20-year spans, something emerges. A rise in low-magnitude earthquakes often comes before a rise in higher-magnitude ones. That’s a correlation: two measurements moving together in a trackable pattern. It suggests a general time window for larger quakes, but it is a broad trend, not an exact prediction tool.
Why does a Big Mac cost $1.26 in one country and $4.90 in another? When you plot Big Mac prices against GDP per capita across 10 countries, you can look for a pattern — do wealthier nations charge more? In poorer countries, the burger price runs high compared to average income. In wealthier ones, it runs low. The data shows a general relationship between the two measurements, but higher national wealth does not always mean a more expensive burger.