Topic 1:
Results from surveys or opinion polls often report a range of values—the sample statistic plus or minus a margin of error (the resulting range is called a confidence interval). This tells us that the range is likely to contain the population parameter.
How much wiggle room we provide is based on how much confidence we wish to have that the range contains the actual population mean. That confidence level is directly related to the middle “truth” area we will accept versus the dubious tail area we will reject—also known as alpha (α). The more confidence we wish to have—the more middle ground we will need to accept (more wiggle room)—thus a smaller tail area. If we insist on a larger alpha (more dubious tail area), we narrow the middle ground we will accept and thus provide less wiggle room—so the more likely it is that we will miss the true average (and, thus, we have a lower confidence level). A 95% confidence level leaves 5% alpha. A 99% confidence level leaves 1% alpha.
