Download
1 / 14
140 likes | 273 Views
What Are We Summarizing?. Lecture 13 Sections 4.1 – 4.2 Wed, Sep 12, 2007. What Are We Summarizing?. How can we summarize data taken from a sample? We want to reduce the data down to a single number (a statistic). What Are We Summarizing?. How best to summarize… Political affiliation?
E N D
What Are We Summarizing? Lecture 13 Sections 4.1 – 4.2 Wed, Sep 12, 2007
What Are We Summarizing? • How can we summarize data taken from a sample? • We want to reduce the data down to a single number (a statistic).
What Are We Summarizing? • How best to summarize… • Political affiliation? • Body weight? • Steak preference (rare, medium, etc.)? • Number of children? • Temperature throughout the day? • What is the difference?
Qualitative Variables • Qualitative variable. • The values of a qualitative variable may or may not have a natural order. • Examples: • Political affiliation. • Steak preference.
Summarizing Qualitative Variables • Typically, we use percentages or proportions to summarize qualitative variables. • 40% of the subjects are Democrats. • 50% of the people prefer their steak medium.
Quantitative Variables • Quantitative variable. • The values of a quantitative variable always have a natural order. • Examples: • A person’s weight. • Number of children. • Temperature.
Summarizing Quantitative Variables • Typically, we use averages to summarize quantitative variables. • The people in the sample weigh an average of 156.2 lbs. • The people in the sample have an average of 2.3 children. • The average temperature for the day was 82.7 degrees F.
Caution • Some qualitative variables may appear to be quantitative. • Rate your own sexual desire: • (1) Way below average • (2) Below average • (3) Average • (4) Above average • (5) Way above average
Caution • If one person selects (2) and another person selects (4), does that mean that the second person has twice the sexual desire as the first person?
Quantitative Variables • A quantitative variable may be continuous or discrete.
Continuous Variables • Continuous variable. • Typically these are measured quantities: length, time, area, weight, etc.
Discrete Variables • Discrete variable. • Typically these are count data • A verbal description usually contains the phrase “the number of.”
Discrete vs. Continuous • Some data may mistakenly be thought to be discrete. • Time • Weight • Clearly, all measurements must be rounded off. But that does not make the quantity itself discrete.
Discrete vs. Continuous • What about heart rate, measured in beats per minute? • It is the basic nature of the quantity that matters, not how we choose to record our observations.
