1. How accurate can models from social media be?

2. Why is assessing personality accuracy based on Facebook data hard?
Personality measured on an arbitrary scale
Why is assessing personality accuracy based on Facebook data hard?
Correlations are not intuitive

3. We can use age to build intuitions about accuracy
Average age in USA: 41 years old
Average SD in USA: 23.5 years old
We can simulate age data and check accuracy at different correlation levels

4. How to assess accuracy well?
Error
Actual age
Predicted age
If Mark is 40 years old, and I predict he is 30, the error is 10 years.
If Sally is 20 years old, and I predict she is 25, the error is 5 years.
If Liz is 35 years old, and I predict she is 55, the error is 20 years.
We can average this error across many people to see how accurate a prediction is on average.

5. How accurately can we predict age?
Random guess
Assume everyone is 41
On average, wrong by 27 years
On average, wrong by 19 years
Prediction with r = .3
On average, wrong by 18 years

6. But…predicted age with .3 looks unrealistic
The predicted scores are clustered heavily around the average—not usable since you would conclude most people are middle aged
So need to spread the scores out to look more like the true distribution
Average error of spread out predictions is 22 years…worse than assuming everyone is average!

7. How accurately can we predict age if we can make more accurate models?
R = 0.5 (quite hard to do)
R = 0.8 (maximum realistic accuracy ever for personality)
On average, wrong by 19 years
On average, wrong by 12 years
R = .95 (extremely unlikely to ever achieve this for anything psychological)
On average, wrong by 6 years

8. Another way to see it….
No relationship
Perfect relationship
R = 0.3

9. Such predictions are useful for understanding the population, but mind control or actual knowledge of specific people is science fiction