1. Introduction
What is statistics?
• Statistics as a subject provides a body of principles and methodology
for :
- (1) designing the process of data collection,
- (2) summarizing and interpreting the data,
- (3) and drawing conclusions or generalities.
Three branches of Statistics
• (1) designing the process of data collection = Experimental Design.
• (2) summarizing and interpreting the data = Descriptive Statistics.
• (3) and drawing conclusions or generalities = Inferential Statistics.
Population vs. Sample
• A (statistical) population includes each element from the set of
observations that can be made.
• A sample consists only of observations drawn from the population.
Population vs. Sample
• The population for a study of how long an infant might be all children
born in the UK in the 1980's.
• The sample might be lengths of all babies born on 7th May in any of
the years.
Population vs. Sample
• We want to know things about populations.
• But we do not have the data of population. Because:
• Collecting the population data often impractical or impossible.
• Instead, we collect a sample data.
• Example: If a company's customer service division wanted to learn
whether its customers were satisfied, it would not be practical (or
perhaps even possible) to contact every individual who purchased a
product. Instead, the company might select a sample of the
population.
Population vs. Sample
• Example:
• You want to know the mean income of the subscribers to a particular
magazine—a parameter of a population.
• You draw a random sample of 100 subscribers.
• The sample mean income is $27,500 (a statistic). You conclude that
the population mean income is likely to be close to $27,500 as well.
Sample Size
• The number of observations in a sample is its sample size.
• Usually, a sample has sample size less than or equal 30 is a small
sample, otherwise it is a large sample.
Group work - Collecting a sample
1) Determine the number of hours per day OU student plan to study.
2) Determine the number of hours per day this year freshman in OU plan to
study.
- Collect a large sample from the population.
- Describe how you collect your sample data.
- Present your sample data.
- Write some comments, or draw some conclusion, hypothesis about the
data.
- Work in group of 2 and turn in a typed-in solution.
- Due: August, 31st.