Psyc_315_-Winter_2010_-_Class_12

Psyc_315_-Winter_2010_-_Class_12 - Chapter 15 Chance or...

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1 Chapter 15 Chance or Probability 2 Inferential Statistics • We now move on beyond mere descriptive statistics. ..to inferential statistics. • Methods used by social and behavioral scientists to go from results of research studies to conclusions about theories or applied procedures. • What most of statistics entails. – You will use this extensively if you go on to complete a degree in psychology. 3 Inferential Statistics Statistics are used to help us make decisions, based on descriptive statistics. • E.g., Does light therapy reduce symptoms of SAD? Statistics can help us estimate characteristics of populations from the scores of a sample. • E.g., Estimating the outcome of an election. www.NationMaster.com
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2 4 Randomness, Uncertainty and Probability Inference statements are everywhere around us: – “ There is a 70% chance of rain today”. “The chance of winning the 6/49 is one in 14 million”. “The chance of getting struck by lightning is one in 250,000”. “There is a 50-50 chance of getting heads when tossing a coin.” Just what is meant by „ chance ‟ in the above statements? Chance is a measure of uncertainty . We call this measure probability . 5 Randomness • The term “randomness” suggests unpredictability. • A simple example of randomness is the tossing of a coin. • The outcome could either be an head (H) or a tail (T). • Because the outcome of the toss cannot be predicted for sure, we say it displays randomness. 6 Uncertainty • At some time or another, everyone experiences uncertainty. • For Example: – Let‟s say you are approaching the traffic signal and the light changes from green to yellow. – You have to decide whether you can make it through the intersection or not. – You may be uncertain as to what the correct decision should be (i.e., “do I walk, do I run for it, or do I wait for the next green light”).
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3 7 Probability • When you ask yourself the question as to whether you believe that you can make it through the yellow light, the answer may be “probably”. • That is, you believe that you can make it across the intersection, but you still may have some doubt. • The concept of “probability” is used to quantify this measure of doubt. 8 Probability • If you believe that you have a probability of 95% getting across the intersection before it turns red, you have made a clear statement about your doubt (i.e., 5% doubt that I will not make it). • The “probability statement” provides a great deal of information. – Much more than statements such as “Maybe, I can make it across,” or “I should make it across,” or “I will probably make it across ”, etc… 9 Random or Probability Experiments • But before discussing the concept of probability, we need to introduce some terms that will be encountered later in this topic. • If we toss a coin, as mentioned earlier, we do not
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Psyc_315_-Winter_2010_-_Class_12 - Chapter 15 Chance or...

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