Week 4 Flashcards
What is a point estimate?
Single value estimate (eg. Max temp. Tomorrow will be 15degrees)
What is an interval estimate?
Range of values (eg. Max temp. Tomorrow will be between 13 and 17 degrees)
What is a confidence interval?
Point estimate +- margin of error
Xbar +- zσ/n^0.5
How to do a confidence interval if σ is unknown and n is less than 100?
Use s to estimate σ, then use t-distribution:
Xbar +- ts/n^0.5
Use n-1 DofF
6 characteristics of t-distribution?
Continuous, symmetrical about mean, mean=0, bell shaped, standard deviations differ according to n, family of distributions
What happens as n increases for a t distribution?
The flatter, more spread out distribution approaches normal distribution as n increases
2 benefits of large samples?
Reduce biasedness
Increase efficiency
What size sample is statistically reliable?
> 100
Why do you need a lower α value for t-distribution when n is small?
Because he rails are thicker when n is small
3 ways to get a large sample?
Time-series method (1 item studied over time)
Cross-section method (many items studied at one point in time)
Panel data method (many individuals studied over time) observations = NxT
How to do a confidence interval if σ is unknown and n is greater than 100?
Xbar +- zs/n^0.5
