วันจันทร์ที่ 13 ธันวาคม พ.ศ. 2553

logistic regression analysis - understanding odds and probability


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to measure the probability and the same probability: the probability of a given result. People use the terms interchangeably possibilities and the chances of a casual use, but this is regrettable. It only creates confusion, because they are not equivalent. They measure the same thing on different scales. Imagine how confusing it would be if people used interchangeably Celsius and Fahrenheit. "There will be 35 degrees today" might actually wear the wrong way.

Remember meback to your introductory course in statistics back to all these problems on the probability of drawing red balls and white balls from an urn. In these problems, the probability of drawing a red ball is measured by how many balls there were in total and how many were red.

In measuring the probability of a result, we need to know two things: how many times something happened and how often it could happen. The result of interest is a success, if it is a good result orno.

The other exit is a failure. Every time you encounter the results is a process called. Since each process in the success or failure, the number of successes and failures in the number of total order must be based on the total number of attempts.

Probability of success is the number the total number of attempts has occurred with respect.

Chances are the number of successes has been the number of errors occurred in the comparison.

For example, the likelihood of accidents in a forecastparticular intersection, every vehicle that is going through an intersection as an attempt. Each study is one of two results: pass or accident. If the result we are most interested in the modeling of an incident that happened (no matter how it sounds morbid) is.

Probability (success) = number of successes / total number of units attempted (success) = number of successes / number of failures

The odds are often written as:

Number of successes: 1 failures

Read 'Number of hits for all faults 1. But often, one will be deleted.

I see a lot of learning when the researchers blocked logistic regression because they are not on the scale used probability thinking of a bet.

Equal opportunities are a first success for every failure 1. 01:01 equal probability .5. A success for all the 2 studies.

The odds are infinity to 0. Odds greater than 1 indicates success rather than failure. Rates of less than 1 indicates the failure is moreas a success.

Probability can range from 0 to 1-area. probability greater than 0.5 indicates success rather than failure. less than 0.5 indicates an error probability is more likely to be a success.

Example: In the last month, shows data from a particular intersection, a .354 that the car drove by him, 72 it was an accident.

72, 1282 incident = = Errors Safe Passage (1354-1372) Total Error = - Pr happened (accident) = 72/1354 = 0.053 Pr Safe (Passage) = 1282/1354 = 0.947 Odds (accident) = 72/1282 = 0.056 Odds (Security) = 1282/72 = 17.87

Now you get the computer because you will see how these relate to each other.

Odds (accident) = Pr (accident) / Pr (security) Odds (accident) = (72/1354) / (1282/1354) = 0.056 (the denominator cancel) Odds (accident) = 1/Odds (Safe Passage) = 1/17.87

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