Presentation on theme: "Section 1 Part 1. Samples vs Population Benefits of getting data from the entire population…. You can draw a conclusion about the entire population….more."— Presentation transcript:
Samples vs Population Benefits of getting data from the entire population…. You can draw a conclusion about the entire population….more accurate Benefits of sampling… Easier to collect the data Cost effective
Good Samples A sample chosen by chance avoid bias by giving all individuals an equal chance to be chosen.
Simple Random Sample (SRS) A simple random sample of size n consists of n individuals from the population chosen in such a way that every set of n individuals has an equal chance of being selected.
Examples of SRS’ Choosing a name out of a hat or cup Using a computer to randomly select the individuals Use a random digit table to select the individuals.
Why is it so important to choose a sample Randomly? ___________________________
How do we randomly choose samples in nature? ________________________________
Bad Samples What make a sample bad? Not representative of the population Biased towards one portion of the population Too small Loaded questions Inappropriate methods of collecting data
Example LOADED Questions “Should the President have the line item veto to eliminate waste?” (97% said yes: ) “Should the President have the line item veto?” (57% said yes: )
Bias The design of a statistical survey is biased if it systematically favors certain outcomes. BIASED SAMPLING METHODS A Voluntary Response Sample chooses itself by responding to a general appeal. Write-in or call-in opinion polls are examples. Ex; Sales feedback at car dealerships Selection of whichever individuals are easiest to reach is called Convenience Sampling. Survey’s in malls
Example Bad Sampling Methods – Create BIAS 5-Star Ford house in DFW asks their customers before they leave the dealership how they would rate their buying experience. If they would give a rating of 5, then they will be placed on the call list for customer service ratings.