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Lecture

# Lab Notes 3.13.14.docx

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Department
Sociology
Course Code
SOC 282
Professor
Dr.Mullan

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In the population H0 is… Reject H0 Do not reject H0 True Type I error (false rejection Correct decision error) False Correct decision Type II error (false acceptance error) • Need population standard deviation to calculate the standard error • A survey asks a sample of 256 respondents their ideal number of children to have; sample mean = 2.11, sample standard deviation = .95; you would like to know if the average ideal of number of children in your population is significantly different (null), or higher than 2. o Conduct one-tailed and a two tailed test to answer questions at alpha level = .05  H0= µ ≤ 2  H1= µ > 2 • We don’t know the population standard deviation so we need to use a t-test  T= xbar-µ / s of x/√n • 2.11-2/0.95/√256 • 0.11/0.059375 • T= 1.85, df=255 (n-1)  H1= µ≠2  Critical value for a one tailed test with an alpha level of 0.05 is 1.65  Critical value for a two tailed test with an alpha level of 0.05 is 1.96  We fail to reject the null hypothesis in a two-tailed test because the t score is less than the critical value • So we can say that from the results from the one-tailed test we can say that the average ideal number of children to have is significantly greater than 2 • So we can say that from the results from the two-tailed test we can say that the average ideal number of children to have is not significantly different than 2 • Questions to ask for interpretation o Did the results reject the null hypothesis? o Did the test results support your research hypothesis? o How to interpret the test results? • For a given alpha level, it’s easier for a one tailed test to reject the null hypothesis (lower critical value, lower threshold) than a two-tailed test (higher critical value, higher threshold) Hypothesis testing for difference between two means • T (n1 + n2 – 2) = ybar 1 – ybar 2 / s of ybar 1-ybar 2 (population mean 1 minus population mean 2) • When two subpopulations have unequal variances use equations of pg. 273-274 o Example: survey shows that the mean housework time per day for British women (n1=733) is 37 min., and 23 min for British men (n2=1219), s1=16 256 and s2=32 1024. Alpha level=0.05 is the mean housework time for British women is significantly greater than, and different from that of men  One tailed: mean housework time of British women is significantly greater than British men’s • H0= µ1 ≤ µ2 • H1= µ1 > µ2  Two taile
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