Experimental Design Data Collection Sampling Techniques

Designing a Statistical Study 1. Identify the variables of interest (the focus) and the population of the study. 2. Develop a detailed plan for collecting data. If you use a sample, make sure the sample is representative of the population. 3. Collect the data. 4. Describe the data, using descriptive statistical techniques. 5. Interpret the data and make decisions about the population using inferential statistics. 6. Identify any possible errors.

Ways to collect data. 1. Observational Study. 2. Perform an Experiment. 3. Use a Simulation. 4. Use a Survey.

Observational Study  The researcher observes and measures the characteristics are areas of interest.  It can be a population or a sample  The observer does not interact with the study participants and should not in any way influence outcomes.  Popular in scientific research.  Dr. Jane Goodall’s work started as an observational study.

Perform an Experiment  A treatment is applied (something is changed) of part of the tested group (population) and responses (changes) are noted.  Researcher deliberately changes something.  Occasionally a “placebo” is used. Discuss the “placebo affect”.  Discuss “blind” and “double blind” testing  Popular in scientific research.

Use a Simulation  A simulation is a mathematical or physical model used to reproduce conditions or situations.  Often uses technology.  Substitute for situations that are too expensive, dangerous or tedious to actually experiment on.  Myth Busters, crash dummies, and computer models.  Show Prob Sim on calculator.

Use a Survey  An investigation of one or more characteristics.  Usually asking questions.  Interview, mail, telephone or computer  Care must be taken to insure that questions are not biased.  A survey can be a Census or a Sampling.  Census is of a Population.  Sampling is of part of a population.  “How do you feel about the new schedule?”

Sampling Techniques/Random Samples A random sample is one in which every member of the population has an equal chance of being selected. We must be careful of sampling techniques to insure that inferences we make about a population is as valid as possible. Assign numbers to all elements of a population and then generate a random list of numbers for the sample size. Show Table and calculator random number generators. Explain with and without replacement.

Sampling Techniques/Techniques Stratified Sample: Members are in strata or subsets. Samples are still randomly selected from the strata. RHS FreshSophJunSen Random 5

Sampling Techniques/Techniques Cluster Sample: Population falls into naturally occurring subgroups called clusters. Select one or more clusters Care must be taken to insure groups are a representation of the population. RHS GeometryAlgebra II

Sampling Techniques/Techniques Systematic Sample: Each member of the population is assigned a number. Surveyor starts at a random point. An even interval of samples are selected. Every “nth” member Must be random. (can not be conducted in freshman hall) RHS 3rd6th9th12th

Sampling Techniques/Techniques Convenience Sample: Whoever is handy. Mall sampling. Our class of junior and seniors. Leads to biased results. RHS Basic Stats

End of the Chapter.  HW Pg 21 Questions 1-28  Next class will be review? Or project.