Estimator is a sample statistic used to approximate a population parameter
 

Comments about Sample means - pg. 289
 

Point estimate of     is 
 

Confidence Interval is a range (or interval) of values that is likely to contain the true value of the population parameter.
 

Associated with Degree of Confidence   is probability   1 -   that the confidence interval contains the true value of the population  parameter.
 
 Often use 90% (=.10),   95% (=.05),   99% (=.01)

Two-Tailed  is z value separating tails   -  and 

Look up    for most common values - Table pg. 292

        for 90% =  1.645

        for 95%   =   1.96

        for 99%   =   2.575

Do #2
 
 
 
 
 
 
 
 
 
 
 

Margin of Error  is how much  standard deviations vary from mean for sample means
   
Calculating if  is Unknown
        If n>30, use s for 
        If n<30 and population is normal, must know 
        Otherwise if n<30 in Section 6.3   t - scores

Confidence Interval
 

where

 
  Procedure in Text pg. 294

Round-off Rule for Confidence Intervals  -
   a)  If data is original Data - one more decimal than values
   b)  Summary values for data -  Same accuracy as 
 
 #8     92% confidence   n = 64 = $23,228,  s = 8779
 
        E =
 
 
 
 
 
 
 
 
 
 

INTERPRETATION of confidence interval:  If took many samples of size 64, 92% of the time the true mean of the population would be in that interval.

      Picture pg. 296   and   Overheads
 
 

#12.     95% confidence,  n = 772, = 69.7     s = 2.8
 
 
 
 
 
 
 
 
 
 

 So what does that mean?

#26       99% confidence
 
 
 
 
 
 
 
 

DETERMINING SAMPLE SIZE

        Solve    for  n to get formula for sample size
 
   
**  Always Round UP!! ***

Again:  If is unknown:  Pg. 299 bottom   Often use s  from a small pilot test
 

#18

96% confidence

E = 2

= 12.46