The correct answer is:

The history instructor has made an error in calculating the correlation coefficient.

Explanation:

The correlation coefficient, denoted by $r$, measures the strength and direction of the linear relationship between two variables. Its value is always between $-1$ and $+1$:

• $r = +1$: Perfect positive linear relationship.
• $r = -1$: Perfect negative linear relationship.
• $r = 0$: No linear relationship.

Since the given correlation coefficient is $1.9$, which is outside the valid range $[-1, 1]$, the instructor must have made an error in the calculation.

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Would you like to learn more about correlation coefficients or their proper interpretation? Here are some related questions:

1. What are the steps to correctly calculate a correlation coefficient?
2. How can we interpret different ranges of the correlation coefficient?
3. What tools or software can be used to calculate the correlation coefficient accurately?
4. Can you explain the difference between positive and negative correlations with examples?
5. What are some common errors when calculating correlation coefficients?

Tip: Always verify your calculations and ensure the data is clean and formatted correctly before applying statistical formulas!