For Which Scatterplot is the Correlation Strongest.
r, and it measures the strength and direction of a linear human relationship between ii variables on a scatterplot. The value of
is always between +ane and –1. To interpret its value, come across which of the following values your correlation
is closest to:
A perfect downhill (negative) linear relationship
A strong downhill (negative) linear relationship
A moderate downhill (negative) relationship
A weak downhill (negative) linear human relationship
No linear relationship
A weak uphill (positive) linear relationship
A moderate uphill (positive) relationship
A strong uphill (positive) linear relationship
A perfect uphill (positive) linear relationship
If the scatterplot doesn’t show that at that place’southward at to the lowest degree somewhat of a linear relationship, the correlation doesn’t hateful much. Why measure the amount of linear relationship if there isn’t much of one?
However, y’all can call up of this idea of no linear relationship in 2 ways: one) If no human relationship at all exists, calculating the correlation doesn’t make sense because correlation merely applies to linear relationships, and 2) If a strong relationship exists but information technology’s not linear, the correlation may be misleading, because in some cases a strong
human relationship exists. That’south why it’due south disquisitional to check out the scatterplot starting time.
Scatterplots with correlations of a) +i.00; b) –0.l; c) +0.85; and d) +0.15
The to a higher place figure shows examples of what diverse correlations look like, in terms of the force and direction of the relationship. Figure (a) shows a correlation of well-nigh +one, Figure (b) shows a correlation of –0.50, Figure (c) shows a correlation of +0.85, and Figure (d) shows a correlation of +0.15.
Comparing Figures (a) and (c), you encounter Figure (a) is nearly a perfect uphill direct line, and Effigy (c) shows a very strong uphill linear blueprint (but not as potent as Figure (a)). Figure (b) is going downhill, but the points are somewhat scattered in a wider band, showing a linear relationship is present, merely not as strong as in Figures (a) and (c). Figure (d) doesn’t bear witness much of anything happening (and it shouldn’t, since its correlation is very close to 0).
Many folks brand the fault of thinking that a correlation of –1 is a bad thing, indicating no relationship. Merely the opposite is true! A correlation of –1 means the data are lined upward in a perfect direct line, the strongest negative linear human relationship you tin get. The “–” (minus) sign but happens to indicate a negative relationship, a downhill line.
How close is close enough to –1 or +1 to bespeak a strong plenty linear relationship? Most statisticians like to see correlations across at least +0.five or –0.v before getting too excited about them. Don’t await a correlation to always be 0.99 still; remember, these are real data, and real data aren’t perfect.
About This Article
This article is from the book:
Statistics For Dummies
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For Which Scatterplot is the Correlation Strongest