July, 2001Guang Jin, Illinois State University Statistics in Applied Science and Technology Chapter 1: Variables and their Measurement

July, 2001Guang Jin, Illinois State University Important Concepts in this Chapter Meaning and Uses of Statistics Descriptive statistics Inferential statistics Variables Stimulus (independent) variable vs. outcome (dependent) variable Retrospective studies Cased-control studies Prospective studies Cohort studies Clinical trials

July, 2001Guang Jin, Illinois State University Statistics: Meaning and Uses Defined: Statistics is a body of techniques and procedures dealing with the collection, organization, analysis, interpretation, and presentation of information that can be stated numerically.

July, 2001Guang Jin, Illinois State University Statistics: Meaning and Uses What can statistics do for you? To understand and critique professional articles To understand evaluations To conduct research/management studies To become a better decision-maker To have a standard professional skill.

July, 2001Guang Jin, Illinois State University In your job, how and where are statistics reported or used? Can you think of some circumstances where you do not feel comfortable reading, critiquing, or using statistics for your job? What examples can this course provide to help you with this job-related applications? STOPTHINKAPPLY

July, 2001Guang Jin, Illinois State University Descriptive statistics vs. Inferential Statistics Descriptive Statistics deal with the enumeration, organization and graphical representation of actual data (observations) Inferential statistics are concerned with reaching general conclusions from incomplete information. It use information from a sample to say something about an entire population. (A sample is a subset of a population)

July, 2001Guang Jin, Illinois State University Variables and Data A variable is a characteristic that can change values from case to case. –Example: age, weight, height, marital status or smoking habits Data: the values of the observations recorded for variables are referred as data.

July, 2001Guang Jin, Illinois State University Variables (Cont’d) Dependent Variable (outcome variable) –described in terms of other variables –it is the thing being predicted –it is the outcome, the criterion, or the response variable Independent Variable (stimulus variable) –describes or predicts a given response variable –it is the thing being manipulated or the treatment –it is the stimulus, the predictor, or input variable

July, 2001Guang Jin, Illinois State University Survey and Experiments Survey: Data from a survey may represent observations of events or phenomena over which few, if any, controls are imposed. The “treatment” group is usually in no way controlled or assigned Experiment: The experiment imposes controls on the methods, treatment or conditions under which it is performed Surveys may be categorized as retrospective or prospective.

July, 2001Guang Jin, Illinois State University Retrospective Studies Retrospective studies (commonly referred to as case-control studies) gather past data from selected cases (individuals with a specific disease or conditions) and controls (comparable individuals without that disease or conditions) to determine differences, if any, in the exposure to a suspected factor.

July, 2001Guang Jin, Illinois State University Prospective Studies Prospective studies (usually cohort studies), in which one enrolls a group of healthy persons and follows them over a certain period to determine the frequency with which a disease develops. The group is divided statistically according to the presence of absence of a stimulus (independent) variable.