PSYC 1010 Lecture Notes - Variance, Standard Deviation, Statistic
3 Jun 2013
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The t distributions are used when we don"t have enough information to use the z distribution. We have to use the t distribution when we don"t know the population standard deviation or when we compare 2 samples to one another. As the sample size gets bigger, the t distributions begin to merge with the z distribution because we gain confidence as more and more participants are added to our study. We don"t know the true value of the population standard deviation ( ). Our best estimate of this population parameter comes from our sample statistic (i. e. , estimate population sd using sample sd) Recall that any sample will be less variable than its parent population. Without correction for this difference, sample variance and sd would give us an underestimate of population variability. When calculating sample variance and standard deviation, use n-1 instead of n to adjust for the bias in sample variability.
