Session #6 -- CONFIDENCE INTERVALS
Oct 2013
TODAY’S OBJECTIVES
1. Understand what confidence intervals tell us
2. Understand how we get them
3. Know the SPSS procedure for getting confidence intervals
Terms to Know
Confidence interval
Mu (μ) t-curve normal curve
RICK’S SITUATION
Recap
His RQ:
Population:
Real population mean:
Sample:
Sample mean: 6
Sampling distribution: 2
Estimated mean = sample mean = 6
Estimated standard error =
CONFIDENCE INTERVALS
Way for rick to talk about how accurate he is
Accuracy in inferential stats
Confidence Interval Statements
Marginal error statements …show more content…
Standardized scores calculating and converting Effect of Sample Size
More accurate population estimates
Narrow confidence interval
Political reporting
increase sample size
As N gets larger, the fraction gets smaller
As the fraction gets smaller, SE gets smaller
As SE gets smaller, the sampling distribution gets narrower
As the sampling distribution gets narrower, more samples become closer to the mean
So the best 95% of the samples are closer to the mean
So the confidence interval for these samples is closer to the mean
So the confidence interval shrinks, and population estimates get more precise and accurate.
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SPSS: Confidence Intervals
This procedure finds statistics about a single variable from a sample, and estimates confidence intervals for the variable.
1. Menu bar, Analyze, Descriptive Statistics, Explore
Opens the “Explore” Box
Variable list on left
Three working areas in the middle
Ignore the second and third
Option buttons on the right
A “Display” area underneath
Five action buttons on the