An Introduction to Things to Come!. Administrivia. The details on the class can be found here: www.stanford.edu/class/hrp259 Class participation plus lots of little assignments and 2 exams determines your final grade.
Weeks of Gestation Please update your virus definitions and scan everything before you send it to me.
Weight at birth
40 weeksWhat We Want….
…and express it with a simple formula like this:
lbs = weeks * something
Outcome = baseline + predictor + predictor
Impact of being a
Weeks * a number
Outcome = baseline + predictor + predictor + error
Impact being a
Weeks * a number
Histogram of actual weights at 40 week births
My model guesses
Histogram of errors at 40 weeks
I guessed way too high rarely
I guessed way too low rarely
0 error if child was 7.5 lbs
Most errors are off by just a bit
If you pretend your variability is normally distributed but your outcome has a limited range, you clearly have problems.
In theory, the variance of count data increases with the mean.
Weight = estimated weight gain each week after conception * number of weeks + weight at 0 weeks
Induced because of HUGE size your outcome has a limited range, you clearly have problems.A True Outlier
From Crawley: Statistical Computing
From Crawley Statistical Computing
Is this better than a flat line at the mean?
Flatten the line, then look up and down to see if you are systematically off.Residuals?
size = intercept + X * something + X2*something else
size = intercept +
X * something +
X2* something else +
X3 * another thing
poly2 = lm(y~poly(x,2))
poly3 = lm(y~poly(x,3))
baseline + predictor + predictor + error
Tweaked outcome =
baseline + predictor + predictor + not normalerror