The raw data (in parts per thousand) are given below.
East West
Previous work stated that the eastern part of the bay had an average salinity of 37 ppt. How likely is it that WW's measurements for the eastern part of the bay were a random sample drawn from a target population with mean salinity of 35 ppt?
Calc > Test allows a t-test of Individual means. Let the null hypothesis be that the sample mean is equal to 37. The alternative is that the mean is not equal to 37. Thus, this is a two-tailed test. Evaluate this test with an alpha of 0.05. Write your interpretation if this null is rejected......if it is accepted (include an assessment of what is "missing" that you would need to make your statement). What is the rational for setting up a problem so that the null hypothesis is rejected? Interpret your results. Evaluate with an alpha of 0.01 and compare with previous results.
Perform a pooled t-test of the difference of sample means for the East and West data sets. The null hypothesis is that the two samples could have been drawn from the same target population. Evaluate with alphas of .05 and 0.01. Interpret.
One of the assumptions is that the two samples have equal variances. Evaluate this assumption. Are there any other assumptions?
WW's friend Jim Bob says that he finds the same species of clam on both sides of the bay and everyone knows that these clams are salty; therefore, he argues that there is no significant difference between the east and west side with respect to salinity.
Perhaps he is correct but we would like to have your opinion. We have been asked to suggest the best place (EOB or WOB) to install a desalination plant and it would be cheaper to start with the freshest water possible.
Your report should include answers to the parts of the questions. Write this up in a logical fashion - that is, what is the problem, what are the assumptions, what are the conclusions. Fell free to import pertinent figures and tables from Data Desk into your report.
What if you plotted the values on a map of the Bay and found that the sample locations were close to roads and beer joints? Add a paragraph discussing the importance of random sampling. How would you suggest that this area be properly sampled?
Dr. WW has undertaken a geochemical survey of the waters in Galveston Bay. Salinity measurements (ppt) were made at 20 different locations -- 10 in the eastern part of the bay and 10 in the western part. Input the following values and compute the means and standard deviations of the two sets of measurements.