PSYC 60 Chapter Notes - Chapter 9: Variance, Null Hypothesis, Standard Deviation
Document Summary
9-1 the t statistic: an alternative to z. 9-1a the problem with z-scores: requires more information than is usually available, requires that we know the value of the population standard deviation, needed to compute standard error. In most situations, standard deviation for population isn"t known variance: use corresponding sample value in place of the unknown. 9-1b introducing the t statistic: sample variance=s2=ss/(n-1, sample standard deviation=s, using sample values, you can estimate the standard error. N: estimated standard error is used as an estimate of the real standard error when the value of is unknown. 2/n: reason for using variance instead of standard deviation: 9-1c degrees of freedom and the t statistic: to determine how well a t statistic approximates a z-score, must determine how well the sample variance approximates the population variance, degrees of freedom=df=n-1. Describes the number of scores in a sample that are independent and free to vary.
