<p>Can someone please explain the difference between t test and Z test and why each one is performed...describe the spread, shape, variance, etc.</p>
<p>thanks!</p>
<p>t test is when you dont know the standard deviation</p>
<p>besides that..</p>
<p>yeah... t curves are used when the standard deviation is unknown and the shape is roughly bell shaped with more "area" in the tails. as the sample size increases, it becomes more like the z distribution.</p>
<p>so the spread is smaller in a z test?</p>