Lecture 1

Question 1

What is the purpose of descriptive statistics?

Answer 1

To reduce, summarize, and describe data.

Question 2

How do we display data?

Answer 2

First, we need to organize the data.

• Usually done by rank ordering the data from highest to lowest
  
  • See Handout #2
• Once we have rank ordered the raw scores, we can assign a rank score to each
• We can group the data into class intervals, called a grouped frequency distribution
  
  • This further reduces & summaries the data
  • Makes info more comprehensible

Question 3

What are the guiding principles of displaying data?

Answer 3

• Make data immediately comprehensible and an accurate picture of the data.
• The # beginning the first class interval is a multiple of the class width
  e. g. 42 in our example is a multiple of 7, 44 (which is the lowest score in the example) is not

Question 4

What is a grouped frequency distribution?

Answer 4

• Much like a histogram, except the point is located above the midpoint of each class interval.
• The points are then joined by a straight line
• Review Handout #4

Question 5

How do you find your class intervals?

Answer 5

• Want between 10-20 class intervals
• Good starting point is Range/10 = (Xmax - Xmin)/10
• See handout #2.1
• In our Eg = 112 - 44/10
• = 68/10
  = 6.8
  Need to change this into the closest odd number (that will result in 10 to 20 class intervals)
  So in this example, our class width is 7
• Also see Handout #3