Assignment 8 Objective: To test examine the probability of a post-operative complication following an appendectomy. Dataset: Appendicitis.sas7bdat Package: SASStudio B. Particulars: 1. The dataset is, as before, appendicitis.sas7bdat. 2. Use the "proc logistic" procedure to estimate the probability of a post-operative complication using the same model as in project 7. The dependent variable is defined as the occurrence of any post-operative complication. 3. Restrict the model to non-elderly adult patients, ages 21 to 64 years of age. The explanatory variables are the same as those you used in the previous exercise. 4. A short video clip is provided on canvas showing the use of the proc logistic procedure. 5. Your focus is "by how much do the odds of a post-operative complication increase for patients who are admitted with complicated appendicitis?" C. Turn in a structured abstract (no more than 300 words, not including the title and section headers, so 307 in total) with the format shown below. a. A point will be deducted if you exceed the word limit. Adhering to the word limit is essential as it forces you to get to the point; at the same time you have to be careful not to omit anything of importance. i. Do not include tables or graphs in the abstract (that would go in the main text or presentation - if you were to do one)! Determine which values from your test(s) are most important to the reader and report those in the abstract. ii. Since the word limit applies to everyone equally, no exceptions will be made!!! Abstract Objective: This contains a brief statement describing the general objective of the analysis. For example "The objective of this analysis is to examine ..." Data and methods: This contains a brief description of the particular dataset used to test the hypothesis. For example, concerning the dataset briefly mention the unit of measurement, whether the data is publicly available, and what types of variables it includes. Results: This contains a brief layman's description of the least squares results and whether the variables were statistically significant. In general there will be one "focus" variable that the story focuses on and is discussed in slightly more detail (this is still an abstract). Select one of the model variables with a coefficient estimate that is statistically different from zero, which you believe is the most interesting from an information stand-point, as your focus variable. Be sure to indicate how the result associated with this variable is interpreted. Conclusions: A very brief statement indicating your conclusions pertaining to the hypothesis - did your results reject the null hypothesis or not? Discussion: This is perhaps the most important section. Here you tell the story of why you believe the analysis was important - why is it "information" and not just "data"? Why would anyone within related professional or policy circles find your analysis and results interesting? How could your analysis help such individuals in terms of decision making? As part of the discussion, indicate whether you would have liked to test the influence of additional variables if they had been available. D. What is important or relevant information is by definition, at least partially, subjective. However, there are certain rules that have to be followed. i. For example, in the results section you should definitely discuss the significance of your test-statistic (at minimum you should provide the pvalue associated with the treatment variable). If you do not, at least one point will be deducted (yes, this is a big oversight). Given the word limit, you may want to group the other variables and report as such. ii. In the methods section, provide a rationalization for using the specific method

************************Data output of SAS FOR LINEAR REGRESSION **************************

Dependent Variable is Operating room Total charges

The REG Procedure

Model: MODEL1

Dependent Variable: TCHGS TCHGS

Number of Observations Read	47460
Number of Observations Used	47460

Analysis of Variance
Source	DF	Sum of Squares	Mean Square	F Value	Pr>F
Model	8	1.842725E13	2.303406E12	2473.72	<.0001
Error	47451	4.418411E13	931152403
Corrected Total	47459	6.261136E13

Root MSE	30515	R-Square	0.2943
Dependent Mean	50896	Adj R-Sq	0.2942
Coeff Var	59.95464

Parameter Estimates
Variable	Label	DF	Parameter Estimate	Standard Error	tValue	Pr>|t|
Intercept	Intercept	1	271956	2177.14211	124.91	<.0001
AGE	AGE	1	91.20939	7.26987	12.55	<.0001
black		1	5684.95352	470.91645	12.07	<.0001
otherNW		1	6813.95711	425.26911	16.02	<.0001
female		1	311.73308	284.31449	1.10	0.2729
hispanic		1	2457.95591	342.49490	7.18	<.0001
uninsured		1	1136.03849	366.21885	3.10	0.0019
complicated	complicated	1	11983	313.34904	38.24	<.0001
SeverityOverall	SeverityOverall	1	-237142	2110.40017	-112.37	<.0001

Logistic regression with Dependent variable =Emergency

The LOGISTIC Procedure

Model Information
Data Set	WORK.APPEND
Response Variable	postOperative	postOperative
Number of Response Levels	2
Model	binary logit
Optimization Technique	Fisher's scoring

Number of Observations Read	28736
Number of Observations Used	28736

Response Profile
Ordered Value	postOperative	Total Frequency
1	1	1848
2	0	26888

Probability modeled is postOperative='1'.

Model Convergence Status

Convergence criterion (GCONV=1E-8) satisfied.

Model Fit Statistics
Criterion	Intercept Only	Intercept and Covariates
AIC	13718.520	10969.309
SC	13726.786	11043.702
-2 Log L	13716.520	10951.309

Testing Global Null Hypothesis: BETA=0
Test	Chi-Square	DF	Pr>ChiSq
Likelihood Ratio	2765.2111	8	<.0001
Score	4864.3455	8	<.0001
Wald	1982.3999	8	<.0001

Analysis of Maximum Likelihood Estimates
Parameter	DF	Estimate	Standard Error	Wald Chi-Square	Pr>ChiSq
Intercept	1	7.5077	0.3847	380.8706	<.0001
AGE	1	0.0101	0.00227	19.9878	<.0001
black	1	0.1945	0.0808	5.7930	0.0161
otherNW	1	-0.1207	0.0913	1.7481	0.1861
female	1	-0.4945	0.0558	78.4029	<.0001
hispanic	1	-0.1497	0.0716	4.3635	0.0367
uninsured	1	-0.0698	0.0639	1.1918	0.2750
SeverityOverall	1	-11.3226	0.3626	975.2230	<.0001
complicated	1	1.1893	0.0551	466.5174	<.0001

Odds Ratio Estimates
Effect	Point Estimate	95% Wald Confidence Limits
AGE	1.010	1.006	1.015
black	1.215	1.037	1.423
otherNW	0.886	0.741	1.060
female	0.610	0.547	0.680
hispanic	0.861	0.748	0.991
uninsured	0.933	0.823	1.057
SeverityOverall	<0.001	<0.001	<0.001
complicated	3.285	2.949	3.659

Association of Predicted Probabilities and Observed Responses
Percent Concordant	85.6	Somers' D	0.712
Percent Discordant	14.4	Gamma	0.712
Percent Tied	0.0	Tau-a	0.086
Pairs	49689024	c	0.856

Frequency distribution of complicated versus uncomplicated Appendicitis

The FREQ Procedure

complicated
complicated	Frequency	Percent	Cumulative Frequency	Cumulative Percent
0	33068	69.68	33068	69.68
1	14392	30.32	47460	100.00