When can we use the z-score? (Since it's impossible to know the population SD) Sometimes I see papers that report the z-score. I am confused because the z-score requires us to know the population standard deviation, which is impossible. What are some reasons people still report the z-score?? Can you give an example please? (The only thing I can think of is when the sample size is large enough so the t-distribution converges to a normal distribution. Also, if the sample is large enough, the sample SD will approximately converge to the population SD. However, even in that situation, shouldn't the researcher report the t-score just to be more sure and conservative?)
Thank you!

When comparing proportions, one way to compute a p-value and confidence interval is to compute a z-ratio also called a z-score. T ratios aren't used.
When comparing means, you are right, I think. The t ratio should be used.
Don't confuse the z-score with "z-factor", which is used when evaluating high-throughput screening of drugs, and has an entirely different meaning than the z-score.
