Confidence intervals

[Maxine450]

What are they, and how do I use them?

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[cham90]

You can find more information than you likely want to know from here: http://www.itl.nist.gov/div898/handbook/prc/section1/prc14.htm

and the Wikipedia page. To quote the former:

The purpose of taking a random sample from a lot or population and computing a statistic, such as the mean from the data, is to approximate the mean of the population. How well the sample statistic estimates the underlying population value is always an issue. A confidence interval addresses this issue because it provides a range of values which is likely to contain the population parameter of interest.

For example, if we randomly select one million Americans and survey their age, we could estimate a median age for the entire country (for our sake we'll say 35 years). But how sure can we be that our finding really is the exact median age when we account for the 350+ million others? Confidence intervals go hand in hand with confidence levels. Through statistical analysis well beyond the scope of the MCAT, we could figure out a range around our finding that has a certain likelihood of being indicative of the whole population. Just to further make up our example, let's say that the statistical analysis reveals a 95% confidence level is + or - 3 years. That means we are 95% sure that the median age for the entire country is between the ages of 32 and 38. A 99% confidence interval would be to be larger, and a 50% confidence interval would be smaller.

If it appears in a passage you should know that it is related to the sample size and the sampling techniques used. A smaller confidence interval for the same % confidence shows more reliable/indicative data.

But more importantly, how does this relate to your MCAT studies?

 

[Maxine450]

Ah, I see thanks. I heard from someone that there was a question about them on the MCAT, which is pretty unusual. Since when have they had statistic stuff on the exam?

 

[costales]

Confidence intervals - and P values - are used in all kinds of reports, but in medicine the range of clinical indifference is just as important.

 

[PingPongPro]

Confidence intervals are probably going to be given in passages with experiments and data of some kind.

To put it simply: It is used to quickly state whether the experiment produced significant results. They usually give you the min and max for the confidence interval. If 1 condition of the experiment has a Max that is smaller than another condition's min, than that indicates it is significant. Basically, if there is no overlap between the confidence intervals of 2 separate conditions, we can be x% confident that there is a real difference between them.