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Stats - Lesson #8

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Amanda Tippetts

on 4 September 2017

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Transcript of Stats - Lesson #8

The Beginning of Correlation and Regression
(lessons 8)

Inherited Characteristics & Genetics
Pearson refined and proved that the current method of calculating the correlation coefficient and least-squares regression line are the optimum values to reduce error.
In 1875, Galton had distributed packets of sweet pea seeds to seven friends; each friend received seeds of uniform weight (also see Galton 1894), but there was substantial variation across different packets. Galton's friends harvested seeds from the new generations of plants and returned them to him (see Appendix A). Galton plotted the weights of the daughter seeds against the weights of the mother seeds. Galton realized that the median weights of daughter seeds from a particular size of mother seed approximately described a straight line with positive slope less than 1.0
Same Correlation but different Slope
Look at the variability of the two variables... even though these data sets have the same correlation, their slope is different because x varies more than y or vice versa.
The slope is determined by the correlation & the standard deviation of the variables. y = r ( Sy / Sx ) x
The Shift from Median and IQR to Mean & Standard Deviation
The Correlation Coefficient
Can you see a z-score in there?
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