Equations
What is the equation for degrees of freedom?
n-1
If Ms. Chambers surveys 13 students, what would her degrees of freedom be?
12
Ms. Chambers surveys half (50%) of the students at the San Francisco Waldorf School. What t testing condition does this not meet?
10% condition
Calculate a t score for a 90% confidence interval with 4 degrees of freedom
2.132
You survey a quarter of the population. Should you use a t score or a normal confidence interval?
Confidence Interval (more than 10% of the population)
What is the equation for standard error?
s/sqrt(n)
If the survey has a sample standard deviation of 0.8 and a survey population size of 15, what is the standard error?
SE=0.207
Ms. Chambers only surveys seniors for her survey about school lunches for all students. What condition does this not meet?
Randomization Condition
Calculate a t score for a 98% confidence interval with 7 degrees of freedom.
2.998
You are working for Apple and only have the capacity to survey 100 of the 1.3 billion iPhone users. Should you use a t score or a normal confidence interval?
T score - less than 10% of the population.
What is the equation for margin of error for a t interval?
SE*t
Calculate the MARGIN OF ERROR for a survey with a standard error of 0.47 and a t score of 2.353.
1.10
The histogram of the survey data is bimodal and symmetric. What condition does this not meet for t testing?
nearly normal condition
Calculate a t score for a 95% confidence interval with a sample population size of 28.
2.052
You make a histogram of your data and the curve is not exactly a normal curve. Should you use a t score or a normal confidence interval?
T score (nearly normal okay)
What is the equation for a t confidence interval?
(ybar-ME,ybar+ME)
Calculate the MARGIN OF ERROR for 90% confidence interval for a survey of 17 people and standard error 0f 0.75
1.3095
At the zoo, they decide to survey 18 of the 76 workers. Would a t test be appropriate? Why or why not?
No, doesn't meet the 10% condition
Calculate a t score for a one tail probability of 0.10 and 20 degrees of freedom
1.325
Give an example of when a t score would be better than a traditional confidence interval.
(varies)
What is the equation for sampling distribution (hint: it's in the first page of the assignment 1 reading)
(ybar-mu)/(s/sqrt(n))
Calculate the CONFIDENCE INTERVAL for a survey with a mean of 87.25, a standard error of 11.7, and a t score of 1.282.
(172.25,102.25)
Chipotle randomly surveys 8% of all orders in their app. They make a histogram of the data and it is unimodal with a slight skew left. Would a t test be appropriate for the data? Why or why not (state conditions)?
randomization - randomly surveyed
10% - 8% is less than 10% of orders
Nearly Normal - while slightly skewed, histogram is nearly normal
Calculate a t score for a one tail probability of 0.005 and a sample population size of 15.
2.977
You are doing a survey of qualitative data. Should you use a t score or a normal confidence interval?
Trick question - neither! You need two quantitative variables for either.