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#1




Calculating the Standard Error of Mean and Confidence Intervals?
A research study is designed to identify the mean body weight of women btwn the ages of 30 and 39.To obtai this,a researcher obtains the body weights of unbiased sample of 81 women in this age group.The mean body wt is 135pounds with a standard deviation of 18.
What is the estimated standard error of the mean for this population? A. 0.05 B. 0.10 C. 1.0 D. 2.0 2. What are, respectively, the 95% and 99% confidence intervals for this sample? A. 131139 AND 130140 B. 130140 AND 131139 C. 129141 AND 130135 D. 130135 AND 129141 E. 131139 AND 129141 
The above post was thanked by:  
aknz (10082011), ashishkabir (05162011) 
#2




SE = sd/sqrt(n)
D) 2.0 95% = Z alpha/2 : 1.96 (close to 2) 99% = Z alpha/2 : 2.58 (close to 2.6) CI = mean +or Z x SE mean = 135 SE = 2 95%CI : 131  139 [131.08, 138.92] 99%CI : 130  140 [129.8, 140.2] 
The above post was thanked by:  
alicante03130 (01262016), ashishkabir (05162011) 
#3




hey..what is sqrt(n)?how did u get answer 2??pls explain in detail pls......and also learn me how did u get Z value??/



#4




Quote:
sqrt = square root 2 formulas you must know: 1. SE = SD / Square root (n) 2. CI = mean + or  [Z score * SE] There is not a formula for Z scores  you have to memorize the values. for the 95% CI: mean = 135 SE = 2 Z score (5% two tailed) = 1.96 = 2.0 135  [2*2] = 131 135 + [2*2] = 139 
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BiostatisticsEpidemiology, Step1Questions 
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