6_Lecture6.1_zScores & probability_0214r_Spring11

6_Lecture6.1_zScores & probability_0214r_Spring11 -...

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1 PSY207 B Spring 2011 Psychological Statistics VI. Probability Objectives You should be able to. ... •Define probability • Compute simple probabilities •Define random samples • Representativeness Finding Probabilities, Proportions, or Percentages Under the Standard Normal Curve VI. Probability 6.1 Probability Probability • What exactly is probability? • And how does probability relate to statistics? 6.1 Introduction to Probability • Research begins with a question about an entire population. • Actual research is conducted using a sample. • Inferential statistics use sample data to answer questions about the population • Relationships between samples and populations are defined in terms of probability
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2 Probability • Inferential statistics are based on probability theory • What’s the probability that the sample you obtained came from the population you thought it was coming from? Definition of Probability • Several different outcomes are possible • The probability of any specific outcome is a fraction or proportion of all possible outcomes outcomes possible of number total A as classified outcomes of number A of y probabilit = Probability • Proportion of times a particular outcome occurs • Number of ways that a particular event can occur divided by the number of ways any event can occur Probability • For the roll of one die, what are all possible outcomes or events? • All possible outcomes = 6 • So what is the probability of rolling a 4? • There is ONE way of rolling a 4, so: • Pr(4) = 1/6 • Pr (A) or p(A): Probability of outcome for event A Probability • Again, how do you make inferences about a population based on a sample? • Look at probabilities “Population”1 ♠♣♣ ♣♥♦ ♠♦♠ ♣♦♠ “Population”2 Sample Which population did this sample come from? 1/6 0/6 Infer
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3 “Population”1 ♠♣♣ ♣♥♦ ♠♦♠ ♣♦♠ “Population”2 Sample Which population did this sample come from? 1/6 3/6 Infer “Population”1 “Population”2 Sample Which population did this sample come from?
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6_Lecture6.1_zScores & probability_0214r_Spring11 -...

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