Apr. 9 Statistic for the day: Number of times a Hummer H2 could be driven around the world on the excess calories Americans consume each year: 244 - PowerPoint PPT Presentation

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Apr. 9 Statistic for the day: Number of times a Hummer H2 could be driven around the world on the excess calories Americans consume each year: 244

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Title: Apr. 9 Statistic for the day: Number of times a Hummer H2 could be driven around the world on the excess calories Americans consume each year: 244


1
Apr. 9 Statistic for the dayNumber of times a
Hummer H2 could be driven around the world on the
excess calories Americans consume each year 244
Source Harpers index
  • Assignment
  • Review for Mondays test using practice problems,
    exercises from book, and lecture notes

These slides were created by Tom Hettmansperger
and in some cases modified by David Hunter
2
  • You should read and review the difference between
  • Categorical and measurement variables
  • Continuous measurement variables and discrete
    measurement variables

  • You should be able to distinguish among
  • Validity of a measurement
  • Reliability of a measurement
  • Bias of a measurement
  • See pp40-43 of the text

3
Categorical, discrete measurement, or continuous
measurement?
(Cat) (CM) (DM) (Cat) (CM) (DM) (Cat)
  • Eye color
  • Weight
  • Number of siblings
  • Gender
  • Time in 100-meter dash
  • Number of cigarettes smoked in a day
  • Building where your first class occurs

4
Consider a clock thats 5 minutes fast.
  • Valid or invalid?
  • Reliable or unreliable?
  • Biased or unbiased?

Answer valid, reliable and biased.
5
Consider a scale that is sometimes several pounds
too low, sometimes several pounds too high
  • Valid or invalid?
  • Reliable or unreliable?
  • Biased or unbiased?

Answer valid, unreliable and unbiased.
6
Confidence intervals
All confidence intervals look like this
Estimate of population value (multiplier)(SD of
estimate)
  • Know how to match up estimate with SD (three
    possibilities)
  • Know how to find the multiplier on p. 137 if I
    give you a confidence coefficient other than 95
    (for 95, the multiplier is 2). By the way, p.
    137 will be provided for you on the test (you
    dont need to copy it onto your sheet of notes).

7
How to create 95 CIs for
  • A population proportion
  • A population mean
  • The difference between two population means

Sample proportion 2(SD of sample proportion)
(SE mean)
Sample mean 2(SD of sample mean)
Diff of sample means 2(SD of diff of sample
means)
8
SD of sample proportion
The standard deviation of the sample proportion
is estimated by
9
SD of sample mean (SE mean)
The standard deviation of the sample mean is
estimated by
This estimate of the SD is called the STANDARD
ERROR OF THE MEAN, or sometimes SE mean or SEM.
10
SD of difference of sample means
The standard deviation of the difference between
two sample means is estimated by
(To remember this, think of the Pythagorean
theorem.)
11
The logic of confidence intervals
What does a 95 confidence interval tell us?
(Whats the correct way to interpret it?)
IF (hypothetically) we were to repeat the
experiment many times, generating many 95 CIs
in the same way, then 95 of these intervals
would contain the true population value. Note
The population value does not move the
hypothetical repeated confidence intervals do.
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