Question

Draw any scatterplot satisfying the following conditions: (a) \(n=10\) and \(r=1\) (b) \(n=8\) and \(r=-1\) (c) \(n=5\) and \(r=0\)

Short answer

The scatterplots should look like the following: (a) 10 points lying along a straight ascending line, (b) 8 points lying along a straight descending line, (c) 5 points scattered without any clear pattern or linear trend.

Step-by-step solution

Scatterplot with \(n=10\) and \(r=1\)

Draw a scatterplot with 10 points that show a perfect positive linear relationship. That means all points should be placed along an ascending line, depicting that as one variable increases, the other one also increases.

Scatterplot with \(n=8\) and \(r=-1\)

Draw a scatterplot with 8 points that show a perfect negative linear relationship. That means all points should be placed along a descending line, depicting that as one variable increases, the other one decreases.

Scatterplot with \(n=5\) and \(r=0\)

Draw a scatterplot with 5 points that shows that there is no linear relationship between the two variables. That means the points should be scattered in a way that doesn't suggest a clear pattern or trend.

Key concepts

Positive Linear Relationship

When we speak about a positive linear relationship in the context of scatterplots, we're referring to a pattern where as one variable increases, the other variable also increases in a consistent manner. This forms a line with an upward slope when graphed. Imagine plotting the hours studied against the grades received - if studying more consistently leads to higher grades, your scatterplot will likely show a line going upwards from left to right.

This relationship is quantified by the correlation coefficient (r). When we have a correlation coefficient of 1, it indicates a perfect positive linear relationship. This means all the data points would lie exactly on a straight, ascending line, leaving no room for any deviation or scatter - like an ideal scenario where every added hour of study guarantees an increase in grades by a fixed amount.

Negative Linear Relationship

In contrast, a negative linear relationship depicts an inverse connection between two variables. As one variable increases, the other decreases correspondingly. On a scatterplot, this is visualized as a line with a downward slope. A real-life example could be the relationship between the speed of a vehicle and the time it takes to reach a destination - as the speed increases, the travel time decreases.

A correlation coefficient of -1 indicates a perfect negative linear relationship, where every increase in one variable is matched by a proportional decrease in the other, without any variation. The points on the scatterplot would be evenly aligned along a descending line. This represents an idealized situation, seldom perfectly encountered in real data.

Correlation Coefficient

The correlation coefficient (r) is a statistical measure that describes the strength and direction of a linear relationship between two variables on a scatterplot. It ranges from -1 to 1 where:

• A coefficient close to 1 suggests a strong positive linear relationship.
• A coefficient close to -1 implies a strong negative linear relationship.
• A coefficient close to 0 indicates no linear relationship.

It's important to note that the correlation coefficient only measures linear relationships and doesn't imply causation. So, even if two variables show a perfect correlation, it doesn't mean that one causes the other to change - it simply describes how well they move together in a linear fashion.

No Linear Relationship

When data points on a scatterplot do not follow a clear linear pattern, we conclude that there is no linear relationship between the variables. In this situation, the correlation coefficient is close to 0, suggesting no predictable change in one variable associated with changes in the other.

This lack of trend means that, for instance, knowing the value of one variable doesn't help us predict the value of the other. The dots on the graph are scattered in a random fashion, not forming any discernible line. In real life, this could represent a scenario where one's favorite music genre has no apparent influence on their mathematical aptitude - one does not tend to increase or decrease in any consistent pattern as the other changes.