Chapter 1: The Nature of Statistics 1.1 Two Kinds of Statistics

Webster’s Definition of Statistics 1. facts or data of a numerical kind, assembled, classified, and tabulated so as to present significant information about a given subject 2. the science of assembling, classifying, and tabulating such facts or data

Descriptive Statistics Methods for organizing and summarizing information Example: baseball statistics – A great deal of time and effort is required to gather and organize statistics – Without them, baseball would be harder to understand

Inferential Statistics Methods for drawing and measuring the reliability of conclusions about a population based on information obtained from a sample of the population Example: political polling – Interviewing everyone of voting age in the US would be expensive and unrealistic – Statisticians sample the population to make inferences about the voting population’s preferences

Population and Sample Population: – The collection of all individuals or items under consideration in a statistical study Sample: – That part of the population from which information is collected

Descriptive/Inferential Stats are interrelated… If you gather information using an inferential method, you’ll use descriptive measures to organize and summarize the data Preliminary descriptive analysis of a sample will often lead you to choose the best inferential method

Descriptive or Inferential?? To classify statistical studies as descriptive or inferential, consider the intent of the study: – If it is to examine and explore the information obtained for its own intrinsic interest only….descriptive! – If it is obtained from a sample of a population and the intent is to use that info to draw conclusions about the population….inferential!

Example 1.3 Table 1.1 displays the voting results for the 1948 presidential election. TicketVotespercentage Truman-Barkley (democrat)24,179, Dewey-Warren (republican)21,991, Thurmond-Wright (states rights)1,176, Wallace-Taylor (progressive)1,157, Thomas-Smith (socialist)139,5720.3

Modern Science of Statistics Births, deaths, marriages, and taxes led naturally to the development of descriptive statistics Roman censuses Inferential statistics developed with Karl Pearson and Ronald Fisher in early 20 th century

Practice Problems P Project Find an article that uses statistics within it. Classify it as either descriptive or inferential, and explain how you reached that conclusion. Can you be 100% certain of this classification? If so, how?