Statistical Analysis

1.

 
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1. Name:
2. Explain how the standard deviation is useful for comparing the means and the spread of data between two or more samples.
3. Does the existence of a correlation always establish that there is a causal relationship between two variables? Use an example to discuss your answer.
4. What is the importance of including the following items when constructing graphs: error bars, trend lines, axis labels, appropriate scale, title, units?
5. The data shows the number of flowers per plant of a random sample from a white clover population.
36, 51, 56, 62, 62, 63, 65, 69, 73, 83
Mean = ?
Mode = ?
Standard deviation = ?
What statistical percentage of the population has between 49 and 75 flowers per plant?
6. The average leaf length of one plant is 2.5 cm with a standard deviation of 0.5 cm. What does this indicate?
A. 95% of all leaves fall within the ranges of 2.0 to 3.0 cm
B. 68% of all leaves fall within the ranges of 1.5 to 3.5 cm
C. 68% of all leaves fall within the ranges of 2.5 to 3.0 cm
D. 95% of all leaves fall within the ranges of 1.5 to 3.5 cm
7. Calculate a t-test for the following data:
Group 1: 6,7,6,8,4,11
Group 2: 3,5,3,2,7,4

t = _____
How many degrees of freedom (df) at in this study ____
What is the critical value for t (2 tailed, .05 alpha) _____
Is the t significant? _____
8. One study of grand juries in Alameda County, California, compared the demographic characteristics of jurors with the general population, to see if jury panels were representative. The results for age are shown below. The investigators wanted to know if the 66 jurors were selected at random from the population of Alameda County. (Only persons over 21 and over are considered; the county age distribution is known from Public Health Department data.) The study was published in the UCLA Law Review.

Age: 21-40
County-Wide %: 42%
# of Jurors Selected: 5

Age: 41-50
County-Wide %: 23%
# of Jurors Selected: 9

Age: 51-60
County-Wide %: 16%
# of Jurors Selected: 19

Age: over 60
County-Wide %: 19%
# of Jurors Selected: 33

Do we have evidence that grand juries are selected at random for the population of Alameda County?
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