SkipCaptcha
3,995
edits
Changes
Jump to navigation
Jump to search
Line 72:
Line 72: + + + + + + + + + + + + + + + + + + + + + + + + + + +
→Correlation and Causation: an example
Additionally, correlation estimates a linear relationship between X and Y. Thus, an increase in variable X is assumed to exert the same influence on Y across all values of X and Y.
Additionally, correlation estimates a linear relationship between X and Y. Thus, an increase in variable X is assumed to exert the same influence on Y across all values of X and Y.
===Example===
Suppose a polling firm was hired to talk to voters as they voted. Each voter was asked "Are you a Republican?", "Are you a blue collar worker?", "Are you male?", "Do you live in West Virginia?", and "Did you vote for Donald Trump?" We can record that data on a spreadsheet using one for yes and zero for no:
{| class="wikitable"
|Person||Republican?||Blue collar?||Male?||Wva?||Trump?
|-
|A||1||1||1||1||1
|-
|B||1||1||1||1||1
|-
|C||1||1||1||0||1
|-
|D||0||1||1||1||1
|-
|E||0||0||1||0||0
|-
|F||0||0||0||0||0
|-
|G||0||0||0||1||0
|-
|correlation coeff||0.75||1||0.73||0.42
|}
Whether the person voted for Trump is the independent variable, and each of the other questions are dependent variables. The correlation coefficient can then be computed comparing the column of each dependent variable with the Trump column. What this data tells us is that being blue collar is a perfect predictor of voting for Trump -- the correlation coefficient is 1. The next best predictive factor would be whether the voter was a Republican, where they match 6 out of 7 times. Then comes gender and West Virginia residence. Assuming that the data sample was large enough to be statistically significant, we could build a model to predict whether other voters would vote for Trump by asking the same questions and computing a score using the formula:
.75*Republican + Blue collar + .73*Male + .42WVa
A perfect score would be 2.896, and someone with a 0 score would be most unlikely to vote for Trump. Of course, the polling firm would be using many more questions and would experiment to fine-tune the questions to get the best predictive scores. They would also use much larger data samples.
This fine-tuning process is a form of learning. When a computer does this by itself it is called [[machine learning]].
==Correlation and Causation==
==Correlation and Causation==