Study GuideStatistics–Common Mistakes and Tables1.Common MistakesStatistics can feel tricky because there aremanyways to make small mistakes. But here’s the goodnews: most exam errors come from a short list of common oversights. If you learn to watch out forthese, you can greatly improve your accuracy and confidence.1. Mixing Up Standard Deviation and VarianceA very common mistake is forgetting whether a formula needsstandard deviationorvariance.•Standard deviation:(σ)or(s)•Variance:(σ2)or (s2)Quick rule:•To getvariance,squarethe standard deviation•To getstandard deviation, take thepositive square rootof the variance2. Confusing One-Tailed and Two-Tailed HypothesesChoosing the wrong type of test can throw off your entire hypothesis test.Use a one-tailed test when:•The hypothesis saysone value is greater than another•Example: “Scores will behigherafter training.”Use a two-tailed test when:•The hypothesis says values will bedifferent, but doesn’t specify the direction•Example: “Scores will bedifferentafter training.” (could be higherorlower)Important reminder:Yournull hypothesisandalternative hypothesismust coverall possibilities:Preview Mode
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