Statistics for the Behavorial Sciences 9th Edition Chap. 9

Question Answer
(Sm) used as an estimate of the real standard error (Om), when the value of O is unknown. Computed from the sample variance or sample standard deviation and provides an estimate of the standard distance between a sample mean M and the population mean U. estimated standard error
used to test hypotheses about an unknown population mean, U, when the value of O is unknown. t statistic
describes the number of scores in a sample that are independent and free to vary. (n -1) degrees of freedom
the complete set of t values computed for every possible random sample size (n) or a specific degrees of freedom (df). Approximates the shape of normal distribution. t distribution
Under what circumstances is a t statistic used instead of a z-score for a hypothesis test? A t statistic is used instead of a z-score when the population standard deviation and variance are not known.
A sample of n=9 scores has SS = 288. Compute the variance for the sample. 36
A sample of n=9 scores has SS = 288. Compute the estimated standard error for the sample mean. 2
True or False. In general a distribution of t statistics is flatter and more spread out than the standard normal distribution. True – As sample size and df increase, the variability in the t distribution decreases, and more closely resembles a normal distribution.
A researcher reports a t statistic with df = 20. How many individuals participated in the study. n = 21
For df=15, find the value(s) of t associated with the top 5% of the distribution. +1.753
For df=15, find the value(s) of t associated with the middle 95% of the distribution. +-2.131
For df=15, find the value(s) of t associated with the middle 99% of the distribution. +-2.947
Sample = n=4, U=40 Treatment sample = M=44, variance s2=16. Is this sample sufficient to conclude that the treatment has a significant effect? No – Fail to reject H0, treatment does not have a significant effect
Sample = n=4, U=40 Treatment sample = M=44, variance s2=16. If all factors remained constant and sample size increased to n = 16, is sample sufficient to prove significant effect? Yes, Reject NO. Treatment has significant effect.
an interval or range of values, centered around a sample statistic. confidence interval
If all other factors are held constant, an 80% confidence interval is wider than a 90% confidence interval. (True or False?) False – Greater confidence requires wider interval.
If all other factors are held constant, a confidence interval computed from a sample of n=25 is wider than a confidence interal computed from a sample of n = 100. True. The smaller sample produces a wider interval.

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