when to use $x$-statistics vs t$-statistics what is $t$ what is standard deviation of a population what is z$ and t$ statistics when to use z-statistics when should we use $z$ statics? when is it appropriate to use $z statistics calculating confidence interval what type of statistic should i use what's the difference between $z$statistics and $t$statistics which statistic is used to calculate the confidence interval when to use $z$statistics what statistic is used to calculate confidence interval how to use z$statistics what is the difference between $z$ and $t$ does statistic use z what is $z$statistics calculating confidence interval using z$ how to calculate confidence interval when to use z$ data