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Exercise 2.143 on page 102 introduces a study that examines the association between playing football. brain size as measured by left hippocampal volume (in \(\mu \mathrm{L}\) ), and percentile on a cognitive reaction test. Figure 2.56 gives two scatterplots. Both have number of years playing football as the explanatory variable while Graph (a) has cognitive percentile as the response variable and Graph (b) has hippocampal volume as the response variable. (a) The two corresponding correlations are -0.465 and \(-0.366 .\) Which correlation goes with which scatterplot? (b) Both correlations are negative. Interpret what this means in terms of football, brain size, and cognitive percentile.

Short Answer

Expert verified
For graph (a) and (b), the correlations are \(-0.465\) and \(-0.366\) respectively. The negative correlation indicates that with an increase in the number of years playing football, both the cognitive percentile and hippocampal volume decrease.

Step by step solution

01

Match Correlations to Scatterplots

To recognize which correlation belongs to each scatterplot, we need to understand that a more negative correlation means a stronger negative relationship between the variables. Graph (a) pairs football years with cognitive percentile, and Graph (b) pairs football years with hippocampal volume. The correlation of \(-0.465\) is more negative than \(-0.366\), hence it indicates a stronger negative relationship. We need to examine both graphs to identify which one shows a stronger negative relationship.
02

Interpret Negative Correlation

Negative correlation implies that as one variable increases, the other decreases. Here, both correlations are negative, meaning that as the number of years playing football increases, both cognitive percentile and hippocampal volume decrease. However, we can’t infer causation from correlation. It doesn’t necessarily mean football causes these decreases, there could be confounding variables.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Negative Correlation
In statistics, a negative correlation between two variables indicates an inverse relationship. This means that as one variable increases, the other tends to decrease. In the context of the exercise, the two negative correlations noted are between years of playing football and two separate outcomes: cognitive percentile and hippocampal volume.

For example, a correlation of \(-0.465\) suggests that as the number of years playing football increases, the cognitive percentile generally decreases. Similarly, a correlation of \(-0.366\) implies that a longer football career might be associated with a lower hippocampal volume. These numbers tell us the direction and strength of the relationship, with \(-0.465\) showing a stronger negative correlation than \(-0.366\).

Understanding that correlation does not imply causation is crucial here. The negative correlation merely suggests a tendency but not a direct cause-and-effect relationship. Other factors could be contributing to this observation. Exploring potential confounding variables—like age, overall health, or training intensity—could provide further insights.
Scatterplot Analysis
Scatterplots are a powerful visual tool used in statistics to examine the relationship between two variables. Each point on a scatterplot represents an observation with its coordinates determined by the two variables being analyzed. In the context of the exercise, scatterplots were used to display relationships between years of football played (explanatory variable) against cognitive performance and brain volume (response variables).

By examining scatterplots, we can visually assess the trend of the data points. When talking about a negative correlation, we often see a downward trend from left to right on the graph. In this exercise, reviewing the scatterplots allows us to identify where the correlation is more negatively inclined by spotting the steeper downward trend, which aligns with the more negative correlation value.

Utilizing scatterplot analysis to see the trend helps to intuitively understand complex statistical relationships. It provides a way to visually detect outliers or any peculiar data patterns that could influence the results, which are not always obvious in numerical data alone.
Cognitive Performance
Cognitive performance refers to the ability to perform various mental tasks, such as memory, attention, and problem-solving. It's often measured by standardized tests that provide scores in percentiles, indicating how an individual’s abilities compare to a broader population. In this exercise, cognitive performance was one of the outcomes related to years of playing football.

The negative correlation between years of playing football and cognitive percentile suggests that longer football exposure may be associated with lower scores in cognitive tests. However, this does not outright signal a decline in cognitive abilities solely due to football. It is important to consider how activities and lifestyle choices or even measurement errors might influence these scores.

Keeping an eye on different studies involving sports and cognitive outcomes is essential to understand the broader implications. Cognitive performance is influenced by many factors, including education, health conditions, and socioeconomic status, which should all be considered when interpreting findings from correlation studies.

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