Day 13: STA205 - Introduction to Statistical Methods

Last time

Next time

• Announcements:
  • Reminder: please hide your rectangles.

  • Your exam is returned.
    • There is a key, made up from your good work.
    • There is a curve:
      • 108 -> 90%
      • 94 -> 80%
      • 80 -> 70%
      • 66 -> 60%
      • 52 -> 50%
      There's a formula for it: \[ newscore=\frac{10*score+180}{14} \]

  • You have a new assignment, due next Wednesday.

  • We will have a quiz this week, over packet 6.

• Today:
  • I wanted to start with a little demo that illustrates the importance of $\alpha$ in an Hypothesis test.

    Here's another demo about Confidence Intervals.

  • One more example, to show you why we do this stuff:

    • Headline: Fracking linked to increased hospitalizations for skin, genital and urinary issues in Pennsylvania: Rashes, urinary tract infections, and kidney stones requiring hospital stays are more common in areas with more drilling, according to a new study

      Researchers found that the more fracking wells were in a county, the more hospitalizations the county saw for genital and urinary problems like urinary tract infections, kidney infections, and kidney stones. Fracking, another name for hydraulic fracturing, is a process of extracting oil and gas from the Earth by drilling deep wells and injecting liquid at high pressure.

    • Now let's check out the research: Unconventional natural gas development and hospitalizations: evidence from Pennsylvania, United States, 2003-2014. I want to look specifically at Table 4. This is why we're studying the things we're studying....

  • Let's get into Packet 6, which has as its major objective determining whether two (categorical) variables are independent of each other or whether they are related to each other.

    I've mentioned this issue in other packets: for example, we're studying violent behavior in KY adults, but if our sampling frame excludes felons, say, we might be skewing our results (if there is indeed a relationship between violent behavior and felon status -- so we might want to study that!).

• Links:

  • Type I and Type II errors

  • Sampling Distribution of the Sample Proportion Calculator

  • The Standard Normal Table of probabilities.