General Homework Comments

1
General Homework Comments

• Final answer for conf. interval or sig. test
  should be complete sentence in terms of context
  of problem (e.g., We are 99 confident that the
  mean healing rate for newts is 25.67 ? 3.1
  micrometers per hour.)
• WORD can insert the symbols µ and ?, and can do
  subscripts. Use these features.
• Hypotheses should be stated symbolically
• H0 µ 5 mm, Ha µ ? 5 mm (for example).

2
Meaning of Significance

• General Idea P probability of observed
  difference if null hypothesis is true.
• Large P-value means observed differences could
  easily occur by chance if null hypothesis is
  true.
• Small P-value means that observed difference have
  small probability of occurring if null hypothesis
  is true.

3
Meaning of Significance

• 14.40
• The observed difference in polyp occurrence
  between the two groups was so small that it might
  reasonably be expected to occur purely by chance
  if we assumed that diet had no effect.

14.42 While there was some difference in richness
and total stem densities between the two areas,
those differences were so small that they could
easily occur by chance if the population means
were identical.
4
Important Ideas from Chapter 15

• For statistical inference to be valid, how
  should the data be produced?

What kind of error does the margin of error in a
confidence interval account for? What kinds of
errors does it not account for?
Explain why "statistical significance" is not the
same as "practical significance." Give an example.
What are Type I and Type II errors?
5
Exam 2Comments

• The exam will cover chapters 7-15 (except for
  chapters 11 and 12).
• I recommend using the review section beginning on
  p. 389 (Exercises II.1II.21, II.24, 25, 30, 31
  would be helpful review problems.)
• You may use a calculator and the formula card
  insert from your text.
• You must take the exam at the time scheduled for
  your section unless you have made prior
  arrangements with me.