1 CHAPTER 4 CHAPTER 4 WHAT IS A CONFIDENCE INTERVAL? WHAT IS A CONFIDENCE INTERVAL? confidence interval A confidence interval estimates a population parameter from a sample statistic at a certain level of confidence: a range within which we expect – i.e., are confident, that the true value to fall. Here confidence means the probability of being right. (We also refer to it as a Confidence Statement.) confidence levelmargin of error (also called sampling error) is We take the sample’s statistic (data) and estimate what the population’s answer would be. This involves how sure we are (our confidence level) and margin of error (also called sampling error) is the margin within which we believe the population’s answer falls.

2 confidence levelmargin of error We take the sample’s statistic (data) and estimate what the population’s answer would be. Involves how sure we are (confidence level) and margin of error (the margin within which we believe the population’s answer falls. (Not required for this course) Formulas are used to calculate Confidence Statements for: A) Data given in percents/proportions. B) Data given in means. (The only difference is a change of formula)

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4 What is a Test of Significance? What is a Test of Significance? Statistical tests determine if the sample statistic (result) gives good evidence against a claim of no effect or no difference. This claim is the null hypothesis. There are two types of hypotheses. 1. Null hypothesis (Ho): There is no difference or no effect of what we are studying (and Hi, which states that there is a difference). Ho is more conservative. The statistical test assesses the strength of the evidence against the null hypothesis. This is the claim we seek evidence against.