qmst notes4 - Degrees of Freedom (df)-How closely the...

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Degrees of Freedom (df) - How closely the scores from a research study approximate the shape of the normal curve. When we calculate the df, we can select an appropriate value from a table of critical values to determine if we can reject the null hypothesis t-test - A basic statistical test to determine if two groups are different from each other. Used when we don't know the population standard deviation. The t-statistic is also known as Student's-t . Developed by William S. Gosset who worked for the Guinness Brewing Co. We use the t-test to determine if differences between two groups are large enough so that we can say that they are drawn from different populations - that differences are not due to sampling error alone. When the sample size increases, the t-distribution increasingly approximates the normal distribution. Note the t curve diagram. To conduct a t-test: We need data measured on an interval or ratio scale, and must assume that the populations from which the samples are drawn are normally distributed. Two major types of t-tests: One-sample t-test -To compare the mean of a sample (x-bar), to a population mean (µ) to determine if a set of observations deviates from a standard or a pattern. Ex: a pharmaceutical company wants to bring to market a new drug that treats a
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This note was uploaded on 01/26/2012 for the course QMST 2333 taught by Professor Mendez during the Spring '08 term at Texas State.

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qmst notes4 - Degrees of Freedom (df)-How closely the...

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