Joe Exotic believes he can change the level of depressive symptoms among tigers with a new treatment.  He conducts a study to determine whether the treatment affects the depression levels of tiger patients who reside at the G.W. Zoo.  He knows that the average depression score of all Tigers is 85 with a standard deviation of 15 (μ=85, σ=15). He administers his treatment, which consists of playing his own country albums on loudspeakers during daylight hours, to a random sample of 20 tigers at G.W. Zoo. After the completion of the treatment the sample exhibits an average depression score of 78 with a standard deviation of 20 (X-bar = 78, s=20). Mr. Exotic would like to know if his depression treatment affects tiger depression. (Use α=.05)

1. What is the null hypothesis?

Note.  In the first field, type either "greater than" (or ">"), "less than" (or "<"), "not equal to" (or "!="), or "equal to" ("="). Do not include any quotation marks in your responses.

In the second field, you should enter the appropriate comparison value.

For example:  

H₀: µ > 0 

or 

H₀: µ greater than 0 

H₀: µ _____________

2. What is the alternative hypothesis?

Note.  In the first field, type either "greater than" (or ">"), "less than" (or "<"), "not equal to" (or "!="), or "equal to" ("="). Do not include any quotation marks in your responses.

In the second field, you should enter the appropriate comparison value.

For example:  

H₀: µ > 0 

or 

H₀: µ greater than 0 

H₀: µ _____________

4. Report the appropriate critical value for this test 

Note. If you considered this test non-directional (two-tailed) and need to report two values (a positive and negative) simply report the absolute value (the positive critical value).  

5. What is the standard error (the denominator of the z_obt or t_obt statistic)?