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# S1 Help watch

1. Hi guys, for Normal distribution, when do I use the normal distribution table i.e. Phi (z) and when do I use the table of percentage points?
Thanks guys =)
2. I assume you're talking about the Cumulative Normal Distribution table and the Inverse Normal Distribution table.

Each reverses what the other does.

Specifically, the Cumulative Normal Distribution table gives you the area under the curve from negative infinity to a positive z value, and the Inverse Normal Distribution table gives you the positive z value from an area from negative infinity to that z value.

You want the area when you're finding the probability given the z value, and you want the z value when you're finding the z value given a probability.

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Updated: March 25, 2013
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