Statistical Analysis Questions  Assignment

1 - Swan-Ganz Catheterization and Patient Demographics (Review Question)

Below is the abstract from the paper  "Effectiveness of Right Heart Catheterization in Critically Ill Patients"  published in JAMA, 1996, by Conners et al.

OBJECTIVE: To examine the association between the use of right heart catheterization (RHC) during the first 24 hours of care in the intensive care unit (ICU) and subsequent survival, length of stay, intensity of care, and cost of care.

DESIGN: Prospective cohort study.

SETTING: Five US teaching hospitals between 1989 and 1994.

SUBJECTS: A total of 5735 critically ill adult patients receiving care in an ICU for 1 of 9 prespecified disease categories.

MAIN OUTCOME MEASURES: Survival time, cost of care, intensity of care, and length of stay in the ICU and hospital, determined from the clinical record and from the National Death Index. A propensity score for RHC was constructed using multivariable logistic regression. Case-matching and multivariable regression modeling techniques were used to estimate the association of RHC with specific outcomes after adjusting for treatment selection using the propensity score. Sensitivity analysis was used to estimate the potential effect of an unidentified or missing covariate on the results.

RESULTS: By case-matching analysis, patients with RHC had an increased 30-day mortality (odds ratio, 1.24; 95% confidence interval, 1.03-1.49). The mean cost (25th, 50th, 75th percentiles) per hospital stay was $49 300 ($17 000, $30 500, $56 600) with RHC and $35 700 ($11 300, $20 600, $39 200) without RHC. Mean length of stay in the ICU was 14.8 (5, 9, 17) days with RHC and 13.0 (4, 7, 14) days without RHC. These findings were all confirmed by multivariable modeling techniques. Subgroup analysis did not reveal any patient group or site for which RHC was associated with improved outcomes. Patients with higher baseline probability of surviving 2 months had the highest relative risk of death following RHC. Sensitivity analysis suggested that a missing covariate would have to increase the risk of death 6-fold and the risk of RHC 6-fold for a true beneficial effect of RHC to be misrepresented as harmful.

CONCLUSION: In this observational study of critically ill patients, after adjustment for treatment selection bias, RHC was associated with increased mortality and increased utilization of resources. The cause of this apparent lack of benefit is unclear. The results of this analysis should be confirmed in other observational studies. These findings justify reconsideration of a randomized controlled trial of RHC and may guide patient selection for such a study.

Research Goal: Compare those that had a right heart catheter used vs. those that did not on the listed demographics.  Conduct an appropriate test to compare the groups on these demographics.  Summarize the results of these  tests.  You will need to use a variety of statistical tests to make these comparisons, all of them will involve using the Fit Y by X option in JMP with X = swang1 (the indicator of right heart catheterization) and Y will be the demographic of interest.

Compare the two groups on these "demographics" and summarize your findings.

a) Age

b) Sex

c) Race

d) Years of Education

e) Income

f) Ninsclass (insurance type)

g) Ca (cancer status)

2 -  Leukocyte Counts in Patients with Colorectal Cancer

Werther et al. examined the -leukocyte count (x109/L) in 51 subjects with colorectal cancer and 19 healthy controls.  The cancer patients were also classified into Duke's classification (A, B, C) for colorectal cancer that gives doctors a guide to the risk, following surgery, of the cancer coming back or spreading to other parts of the body.  An additional category (D) identified patients with disease that had not been completely resected.  The results are contained the file Leukocyte Count.JMP.  Perform an analysis of these data, determined first if the groups differ significantly in terms of mean leukocyte count.  Also if the groups do differ in terms of the mean leukocyte counts, conduct appropriate multiple comparisons to determine which groups significantly differ.  Summarize all results.

3 - EMG values and Angular Position

Eleftherios Kellis conducted an experiment on 18 pubertal males.  He recorded the electromyographic (EMG) activity at nine angular positions of the biceps femoris muscle.  The EMG values are expressed as a percent (0-100 percent) of the maximal effort exerted with the muscle and present an average in a range of flexion angles.  The nine positions correspond to testing knee flexion angles of 1-10^o, 11-20^o, 21-30^o, 31-40^o, 41-50^o, 51-60^o, 61-70^o, 71-80^o, and 81-90^o.  The results are displayed in the following table.  For subject 1, for example, the value of 30.96 presents the average maximal percent of effort in angular positions from 1 to 10 degrees.  Perform an analysis of these data, determined first if the angle ranges differ significantly in terms of mean maximal percent effort. Also if the groups do differ in terms of the mean maximal percent effort, conduct appropriate multiple comparisons to determine which angle ranges significantly differ.  Summarize all results.  The data file is called EMG values.JMP.

Attachment:- Statistical Analysis - Assignment.rar