Question

Joseph claims that a scatterplot in which the y-values increase as the x-values increase must have a linear association. Amy claims that the scatterplot could have a nonlinear association. Which statement about their claims is true?
Joseph is correct because only a line will increase along the whole data set. The scatterplot will have a positive, linear association.
Joseph is correct because only a line will decrease along the whole data set. The scatterplot will have a negative, linear association.
Amy is correct because a nonlinear association could increase along the whole data set, while being steeper in some parts than others. The scatterplot could be linear or nonlinear.
Amy is correct because only a nonlinear association could increase along the whole data set. A line has the same slope at any point, but a curve can get steeper at different points.

Answer 1

Answer: Choice C

Amy is correct because a nonlinear association could increase along the whole data set, while being steeper in some parts than others. The scatterplot could be linear or nonlinear.

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Explanation:

Just because the data points trend upward (as you go from left to right), it does not mean the data is linearly associated.

Consider a parabola that goes uphill, or an exponential curve that does the same. Both are nonlinear. If we have points close to or on these nonlinear curves, then we consider the scatterplot to have nonlinear association.

Also, you could have points randomly scattered about that don't fit either of those two functions, or any elementary math function your teacher has discussed so far, and yet the points could trend upward. If the points are not close to the same straight line, then we don't have linear association.

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In short, if the points all fall on the same line or close to it, then we have linear association. Otherwise, we have nonlinear association of some kind.

Joseph's claim that an increasing trend is not enough evidence to conclude the scatterplot is linear or not.