conf intervals

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mrb102189

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In calculating ranges using given confidence levels, I’m confused as to what is expected from candidates…do we need to memorize the common confidence levels? As in:
-95%=1.96 or 2
-90%=1.645 or 1.65
-68%=1
I hope I am not mis-remembering here, but I belive I’ve answered some Kaplan questions that DON’T provide a snapshot of the Z table indicating we have to memorize these common Z values (which is abolutely doable), but I also beleive I’ve come across exmaples where they give you a snapshot of the Z table to use.
What should I expect on the exam? Should I have common crititcal values memorized and if so, which ones?
Thanks!
 
I wouldn’t worry too much about memorizing a lot of Z, Chi, T, F values. But assume that in statistics, knowing that 95%=1.96 or 90%=1.65 at 1-tailed distribution is like knowing 11^2 = 121 and 12^2 = 144 in algebra/arithmetics. I mean, they are too much used, almost always, that memorizing them is a lot of help.
 
That’s essentiallywhat I was thinking…thanks!
 
You do need to know the common z-table values:
  • μ ± 1σ : 68%
  • μ ± 1.645σ : 90%
  • μ ± 1.96σ : 95%
  • μ ± 2.58σ : 99%
 
Memorizing it helps me solve a question in less time.
 
Agree with S200 here, memorize the distributions from the normal distribution.
In addition I feel like more common exam questions would center on the tradeoff between precision and the size of the interval or dealing with moving from confidence intervals to the level of significance and understanding the impact of using degrees of freedom in a sample vs. population confidence interval (i.e. comparing the shape of the Student T distribution with various DOF to the normal distribution).
That said the curriculum does give a couple of equations that are more in the weeds:
Confidence Interval = Point Estimate ± (reliability factor x standard error)
and several equations for confidence intervals with normal distribution with either known or unknown variance
 
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