Psyc_315_-Winter_2010_-_Class_19

Psyc_315_-Winter_2010_-_Class_19 - 1 Sample t-Test Recap...

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1 Sample t-Test Recap and Practice Problems 2 Standard Error • Standard error provides a measure of how well a sample mean approximates the population mean. • That is how much difference is reasonable to expect between a sample mean and the population mean. • In most cases, however, SD for the population is not known. The whole point for conducting hypothesis testing is to gain knowledge about an unknown population. . M Pop SD SD n = = 3 Estimated Population Variance and Standard Deviation • One can estimate the population variance and standard deviation using the sample variance. • Use n-1 instead of n, this corrects for the bias in sample variability – because variability of samples is generally less than that found in a population. • Dividing by a smaller number produces a larger result and makes sample variance an accurate or unbiased estimate of population variance. 2 2 ( ) 1 X M SS s N df - = = - n
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4 Sample Variance and Standard Deviation • Sample mean = 5.0 • Sample Variance = 36/(7-1) = 36/6 = 6.0 • Sample Standard Deviation = 6 = 2.45 • Note: Use sample mean when calculating squared deviations. X (X-M) (X-M) 2 1 -4 16 6 1 1 4 -1 1 3 -2 4 8 3 9 7 2 4 6 1 1 X=35/7 = 5 =36 5 Estimated Standard Error • It is an estimate of the real standard error when the population variance or standard deviation is unknown. • Estimated Standard Error:
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Psyc_315_-Winter_2010_-_Class_19 - 1 Sample t-Test Recap...

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