Chi Square GOF test
Chi square for independence/homogeneity
Comparing 2 sample proportions/means
Trivia
111
When should we use the chi-square test for goodness of fit?
When you are testing to see if the observed variables match the expected variables.
111
What is the chi square test for homogeneity?
One variable, 2 populations
111
What is the inference method for significance test for comparing 2 sample proportions and means?
2 sample z-test for difference (p1-p2)
2 sample t-test for difference (m1-m2)
111
Can a crocodile stick its tongue out?
No
222
A box of crayons contains 38 crayons of the 3 same colors. There are 18 pink crayons, 18 blue crayons and 2 purple. A random sample f 200 people is taken and what color out of the 3 colors they pull out of the box. Find the X2,DF, and p-value.
X2=4.07
DF=2
p-value=.1306
222
We surveyed 2 samples of students in different grades and asked if they would go to disneyland. What are the expected values if there is no difference?
222
How do you find pooled sample?
P1 = a/b
P2 = c/d
Pc = a+c/b+d
222
What is the bodies strongest muscle?
Tongue
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If the Ho is true, what does the p-value tell us?
If the Ho is true, then the p-value=the probability we got the sample that we did.
333
What is the chi square test for independence?
2 categorical variables that are associated, 2 variables, 1 proportion
333
In 2008, 2 students were done about who was on team Edward rather than team Jacob from the twilight franchise. The first study of an SRS of 800 teens found that 73% of teens preferred Edward, and the second study of teens of an SRS of 2253 found that 47% were team Edward. Use these results and construct a 95% Confidence Interval for the difference between the proportion of all teens who are team Edward
We are 95% confident that the interval from .223 to .297 contains the true difference in the proportion of teens who are team Edward.
333
What color were stop signs before they were red?
Yellow
444
A disneyland worker wonders if the visitors are equally likely to ride each of the 3 most popular rides at disneyland. The worker selects a random sample from all visitors who are entering the park, so that wait time for the rides does not include their answers. Find the expected values and X2.
Expected values: 155,155,155
X2= 3.46
444
The table below shows the results of a survey asking if they have all A's in school. Calculate X2, DF, and p-value?
X2=6.76
DF=3
p=.0798
444
We want to test whether there is a difference between the proportion of staff members working between Phantom of the Opera and Hamilton that have once been audience members at the show they work for. A theater addict took an SRS of 100 hamilton staff and 200 phantom staff and recorded the proportion of staff who have been audience members. FOr hamilton 70/100 of the staff have once been audience members and only 100/200 have for phantom. Hamilton and phantom each have 1000 actors/staff working full time on set. DOes this data give convincing evidence that there is a difference? Test at a .05 significance level
4.65e-4 (0) < .05
Reject Ho Conclude Ha that there is a differnece between the proportion of staff members at both shows who have once been audience members.
444
How much of your brain is fat and how much of your brain is water? (in percents)
75% water
60% fat