Exam 10: The Hypothesis of Difference

When there is a significant difference in the population, then a powerful statistical test is likely to detect that difference.

For the independent t test, the null hypothesis states that the samples

Whenever the distribution of differences is normally shaped, and all its assumptions are met, then

When the two sample means are equal, the t ratio will always lead to an accept of the null hypothesis.

When a difference is said to be "significant", it means that the difference probably

When the alternative hypothesis is accepted, then

The estimated standard error of difference is an estimate of

As was true for the z test, the t ratio assumes that all the parameter values are known.

A group of 20 violent drug abusers, all of whom had committed homicide while under the influence of a psychostimulant, was selected from the population of a certain prison. Half the men had been cocaine abusers while the other half had been on methamphetamines. All were abstinent at the time of testing. The men were tested on the CAQ (Clinical Analysis Questionnaire) and their Factor Q1 scores were compared (Factor Q1 includes Radicalism, Hypochondriasis and Boredom & Withdrawal). Their scores, converted to T scores, were as follows: Cocaine Group: 65,58,65,62,60,61,70,71,68,75. Methamphetamine Group: 60,53,52,55,54,59,62,60,60,56 -Find the means for each group.

A researcher selects a pair of random samples. In Group 1 the scores are 20, 14, 16, 18, 16, 15, 14. In Group 2 the scores are 23, 20, 21, 24, 18, 22, 24, 22, 20, 20. Find the standard error of difference.