他们收集的数据涉及到14种变量，包括人类身高，黄金价格，树木年轮密度，以及欧洲工业化之前公元1500年到1800年之间的温度变化。

They collected data on 14 variables, such as human height, the price of gold, tree ring width, and temperature from pre-industrial Europe between the years 1500 and 1800.

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解剖树木生长过程木材密度变化规律，研究年轮内密度的变化十分重要。

So it is very important to find out the variation regulation of wood ring density in growth process.

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