Extra credit

Mark W. Tengler, M.S. PSYC 2317

1

INFERENTIAL STATISTICS Extra Credit #2

Directions: Answer the questions with the data that is given and only using your formula

worksheets and the statistical tables from the class (t Distribution and F Distribution tables). Please show the complete diagram of the research design and all of your work. Please set up tables to do your calculations similarly to how we did it in class, and then plug the numbers into the correct formulas. Please work individually. This exercise is worth 10 points extra credit and is due on the final exam day.

Single Sample Design:

Numerous studies have shown that IQ scores have been increasing, generation by generation, for years (Flynn, 1984, 1999). The increase is called the Flynn Effect, and the data indicate that the increase appears to be about 7 points per decade. To demonstrate this phenomenon, a researcher obtains an IQ test that was written in 1980. At the time the test was prepared, it was standardized to produce a population mean of µ = 100. The researcher administers the test to a random sample of n = 16 of today’s high school students and obtains a sample mean IQ of M = 121 with SS = 6000. Is this result sufficient to conclude that today’s sample scored significantly higher than would be expected from a population with µ = 100? Use α = .01.

Two Independent Groups Design:

A biopsychologist studies the role of the brain chemical serotonin in aggression. One sample of rats serves as a control group and receives a placebo. A second sample of rats receives a drug that lowers brain levels of serotonin. Then the researcher tests the animals by recording the number of aggressive responses each of the rats display. For the data below, is there a significant effect of the drug on aggression? What, if any, role does serotonin has in aggression? Use an alpha level of α = .05. (Note: is this a one-tail or two-tail test?)

Lowers Serotonin Control 5 3 8 6 15 5 16 6 6 8 9 4 7

Mark W. Tengler, M.S. PSYC 2317

2

Three or More Independent Groups Design:

A developmental psychologist is examining problem-solving ability for grade school children. Random samples of 5-year old, 6-year old, and 7-year old children are obtained with n = 3 in each sample. Each child is given a standardized problem-solving task, and the psychologist records the number of errors. The data are as follows:

5-year olds 6-year olds 7-year olds 5 6 0 4 4 1 6 2 2

a. Does the data indicate whether there are any significant differences among the three age groups? Use α = .05. Show the complete design, all your work, and report your results professionally.

One Way ANOVA: Complete the matrix for the following scenario: A developmental psychologist is examining the development of language skills from age 2 to age 4. Three different groups of children are obtained, one for each age, with n = 18 children in each group. Each child is given a language-skills assessment test. The resulting data were analyzed with an ANOVA to test for mean differences between age groups. The results of the ANOVA are presented in the following table. Fill in all missing values, using your knowledge of the relationships within the table. (Hint: Start with the df values first, which you can calculate from your formula sheet.) Show your work and all calculations.

Source

SS

Df

s2 or MS

F ratio

Between groups

48

______

______

F = ______

Within groups

______

______

______

Total

252

______