T Value And Z Value. Normally you use the t table when the sample size is small n 30 and the population standard deviation σ is unknown. As the data size increases distribution tends to be z distribution.
Z score ranges from 3 to 3 while the t score ranges from 20 to 80. Similarly for a large sample we have a high degree of freedom. For a large sample size sample variance will be a better estimate of population variance so even if population variance is unknown we can use the z test using sample variance.
As the data size increases distribution tends to be z distribution.
Z scores are based on your knowledge about the population s standard deviation and mean. Z scores are based on your knowledge about the population s standard deviation and mean. Normally you use the t table when the sample size is small n 30 and the population standard deviation σ is unknown. T scores are used when the conversion is made without knowledge of the population standard deviation and mean.
