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    $\begingroup$ Thanks, this was really helpful, I knew I was over-complicating it as the t-test for larger n approaches the normal. So strictly speaking, even if n was 1000 the t-test should be used if SD not known a-priori? $\endgroup$ Commented Feb 7, 2014 at 20:36
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    $\begingroup$ You're welcome. Strictly speaking, yes, but note that it will be very difficult to tell the difference between the $t$-distribution & the normal distribution at that point. $\endgroup$ Commented Feb 7, 2014 at 20:40
  • $\begingroup$ Yes, definitely. Sorry to have been so finicky, just difficult trying to think of how to explain it to others in quite a black and white way. Appreciate your help thanks! $\endgroup$ Commented Feb 7, 2014 at 20:42
  • $\begingroup$ Also note that calculating the t-test results is for all intents and purposes without meaningful extra computational cost nowadays. We are no longer looking up test statistics in some paper tables that cannot cover all the cases, we are just asking the computer. So, why bother and worry about whether you could perhaps also get the same results using a z-test? $\endgroup$ Commented Jul 17, 2017 at 11:12