Statistical Reasoning for everyday life Intro to Probability and Statistics Mr. Spering – Room 113

1.4 Believing Statistics?? Check IN????  Have you ever heard an unbelievable statistic or claim? How did you react?  Research Shows????? Show me the research? When should you believe a statistical study?

1.4 Believing Statistics?? Most researchers conduct studies with honesty and integrity However, bias can arise in many ways. Thus we examine statistics carefully, looking for anything that might cause question. “BE METICULOUS!” No definitive way to ask “Should I believe a statistical study?” Nevertheless, the following guidelines can be helpful.

1.4 Believing Statistics?? Eight Guidelines for Evaluating a Study 1. Identify the goal, population, and type of study 2. Consider the source, are they biased 3. Question the sampling method, “Is it representative?” 4. Look for problems in defining or measuring variables of interest 5. Watch for confounding factors that can invalidate conclusions TO BE CONTINUED….

1.4 Believing Statistics?? Eight Guidelines for Evaluating a Study 6. Consider any survey, looking for anything that might produce inaccurate or dishonest results 7. Check that results are fairly represented in graphs and concluding statements, both researchers and media often create misleading graphics or jump to conclusions not supported by results. 8. Finally, consider the conclusions. Do the conclusions make sense? Do the results have any particular significance? Did the study achieve its goals? Use your own judgments to extend these guidelines!

1.4 Believing Statistics?? Bizarre Factoid: Statistic: 3% of pet owners give Valentine's gifts to their pets on Valentine's Day. ??? The only guy without a beard in the band ZZTOP is…. Frank Beard

1.4 Believing Statistics?? Consider the source: Help prevent problem studies by using Peer Review.  Peer review – Process in which several experts in a field evaluate a research report before the report is published.

1.4 Believing Statistics?? Examine the Sampling Method: Poor sampling methods almost guarantee bias. (GALLUP) Check for these confounding factors –  Selection bias (selection effect) – occurs when sample chosen in biased way  Participation bias – occurs when subjects in study are voluntary  Voluntary response survey – remember self-selected survey and convenience sampling

1.4 Believing Statistics?? Variable – item or quantity that can vary or take on different values Variables of interest – items or quantities that the study seeks to measure Problems in defining or measuring variables: Results of statistical studies are harder to interpret and seem viable if the variables under study are difficult to define or measure

1.4 Believing Statistics?? Watch out for confounding variables: Often, other variables that are not part of the study can make it difficult to interpret results. Confounding factors → confounding variables Confounding variables can affect a study’s results if they have not been accounted for, they are difficult to discover, and sometimes they are never discovered.

1.4 Believing Statistics?? Consider the wording of a survey: Unfortunately most people do not have a problem with lying → avoid sensitive subjects Availability error – people are more likely to choose the item that comes first in a survey because of a tendency to make judgments on what is most available in the mind.

1.4 Believing Statistics?? Stand back and consider the conclusions:  Did the study achieve its goals?  Do the conclusions make sense?  Can you rule out alternative explanations?  If conclusions make sense, do they have significance? (i.e. losing half a pound, killing 5 bacteria, saving 2 minutes) Extraordinary claims require extraordinary evidence! -Carl Sagan

1.4 Believing Statistics??

Why is a self-selected survey always prone to bias? People who feel strongly about an issue are more likely to respond, therefore the opinions of the respondents is unlikely to represent the opinions of a larger population. What are confounding variables? Confounding factors

1.4 Believing Statistics?? HOMEWORK # 4: pg 42 # 6-30 even BE INQUSITIVE!