Estimating with uncertainty

M. Drew LaMar
February 1, 2017

“Absolute certainty is a privilege of uneducated minds and fanatics. It is, for scientific folk, an unattainable ideal.”

- Cassius J. Keyser

Introduction to Biostatistics, Spring 2017

In The News

In a post-truth world, statistics could provide an essential public service

John Pullinger

http://tinyurl.com/z9pwk2d

In The News

In a post-truth world, statistics could provide an essential public service

John Pullinger

Quote: Statisticians can now amass more data more quickly than ever. This could help us to make decisions based on real numbers, not prejudice.

Quote: Of course decisions are made on the basis of emotions and beliefs as well as science. Those of us who work in the world of data need some humility in what we claim. But good evidence does matter.

http://tinyurl.com/z9pwk2d

Course Announcements - Lab #3/4

  • DataCamp: Intermediate R
    • Lab #3
      • Chapter 1: Conditionals and Control Flow
      • Chapter 2: Loops
    • Lab #4
      • Chapter 3: Functions
      • Chapter 4: The apply family

Course Announcements

  • Reading Assignment for Friday - W&S, Chapter 5 (QUIZ)
  • Homework #3 is posted and due on Monday, February 6, 5:00 pm
  • START ON HOMEWORK EARLY!! Again, recommendation is to start labs before lab time (so you can ask pointed questions during lab), and use lab time as a time to work on homework.

Finishing up Descriptive Statistics...

Make sure you read the book for the following discussions

  • How to compute a mean and standard deviation from a frequency table

Question: Why is this important to know?

  • Rounding rules for displaying tables and statistics
  • Effect of changing measurement scale
  • Cumulative frequency distributions (we will cover this later as well)

My point here is that you are responsible for all book material, even if we don't cover it in lecture!

Describing data in R

Measures R commands
\( \overline{Y} \) mean
\( s^2 \) var
\( s \) sd
\( IQR \) IQR\( ^* \)
Multiple summary

\( ^* \) Note that IQR has different algorithms. To match the algorithm in W&S, you should use IQR(___, type=2). There are different algorithms as there are different ways to calculate quantiles. (for curious souls, see ?quantiles). For the HW, either version is acceptable. Default type in R is type=7.

Describing data in R

Measures R commands
\( \overline{Y} \) mean
\( s^2 \) var
\( s \) sd
\( IQR \) IQR
Multiple summary 
summary(mydata)

    breadth     
 Min.   : 1.00  
 1st Qu.: 3.00  
 Median : 8.00  
 Mean   :11.88  
 3rd Qu.:17.00  
 Max.   :62.00

IQR would be \( 17-3 = 14 \).

Online Tutorials - Estimating with Uncertainty

Sampling distributions and confidence intervals