But otherwise, I doubt the age gap in this relationship poses many more complexities than your average relationship.

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One of her main research projects looked at the relationship between self-control and grade-point average.

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One medical student interested in applying cold called a few finance professors and created his own valuation technique, using a formula including the relationship between the number of Facebook friends and the average product price.

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It did not test many other widely used indicators, such as the relationship between the current price of a share and its 200-day moving average.

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The relationship is strong enough, Ms Van Rijckeghem and Ms Weder reckon, to suggest that raising average civil-service pay from 100% to 200% of the manufacturing wage reduces corruption by about one unit in the corruption index.

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The findings indicated the relationship between birth weight and pollution was dose related - the higher the exposure, the lower the average birth weight.

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