05. Chance or Significant?

Class Five: Some Clean Up, Probability

• z-scores for comparison

  • SAT N(1000, 200)

  • ACT N(18, 6)

  • normal distribution table

    • so what does this do for us?

    • ok, so imagine we want to make a program that allows us to get better at SAT

      • get 10 people. have them take the SAT after doing our program

        • yes, all kinds of problems here

      • compare what they did to the average:

        • did they do better?

        • how much better?

        • is it significant?

• What Went Wrong in Michigan?

  • fivethirtyeight on the issue

  • Alex dug in and found this pretty awesome piece of information:

    • • Ended calls with anyone who responded "not sure" when asked which party's primary they were voting in.

    • And this quote from their methodology:

      • Federal law only permits us to call land lines using automated polling. Because likely Primary voters are older, 52% are 60 or older and 76% are older than 50, we believe there are sufficient land line voters to get an accurate sample. We do not have to make any assumptions of likely voter turnout.

  • redditor /u/_supernovasky_:

    • I'm going to break rank as a stats guy here: The polls were tremendously wrong. My model will end up reflecting this result and look poorly on many polls. Demographics > polls is what this race tells me, and this has been an ongoing story of the race for Clinton AND for Sanders.

    • Kent County is what flipped this entire race for Sanders. Kent county is highly non-white. Black and Hispanic votes are big here. It was hit very hard by the trade deals and lost SO many manufacturing jobs over time. I said that if Sanders criticism on trade deals was compelling, Kent County would show it. She was favored to win by 9%. She is losing by 30% here. I would say they were compelling.

• Probability (Naked Stats)

  • plinko machine

• Standard Deviations

  • coin flipping experiment

    • four choices

    • six choices

• Big Ideas:

  • things happen by chance all the time. our job is to try and figure out--is it by chance or by something else?

  • gambler's fallacy swings both ways, but only exists because we KNOW the true outcomes.

    • what happens with a die that's weighted? How do we know that a die is weighted?

    • real=c(1,2,3,4,5,6)

      • sample(real,10,replace=T)

    • weight=c(1,2,2,3,3,4,4,5,5,6,6,6)

      • sample(weight,10,replace=T)

HW:

• • • take the State Data and make something interesting that fits what we know about making good graphs

      • columns:

        • State Name,

        • Average Teacher Salary,

        • Percent of Students in the State Taking the SAT

        • Average SAT Verbal Score

        • Average SAT Math Score

    • Naked Statistics, Chapter 5 1/2: The Monty Hall Problem (which we will discuss in class)