There is a great deal of debate in the medical community concerning how to treat pregnancies when the mother is pregnant with twins.
Some doctors believe that when the mother shows certain symptoms before the due date (i.e., preterm), it is best to induce labor or perform a cesarean; other doctors think that preterm births should be allowed to occur without induced labor or a cesarean. Still other doctors believe as much as possible should be done to promote a full term pregnancy.
The head of the birthing center at a large city hospital examined the hospital's twin birth records for several years. The data is summarized in the table below and is in this Excel file: Twin Births
1999 2004 2009
Preterm (induced or cesarean) 11 13 19
Preterm (without procedures) 13 14 18
Full term 27 26 32
Important Note: To arrange the data in the Excel file into a table in the worksheet, do the following:
1) click on any cell in the data;
2) click on the Insert tab;
3) click on PivotTable at the extreme left of the menu ribbon;
4) in the resulting window check that the Table/Range area shows Sheet1!$A$1:$C$10; in addition, click the radio button next to "Existing Worksheet" and specify the address of an empty cell in the "Location" area; then click OK;
5) in the PivotTable Field list, drag Duration to the Row Labels area;
6) in the PivotTable Field list, drag Year to the Column Labels area;
7) in the PivotTable Field list, drag Counts to the Values area;
8) you should now have a table showing the number of pregnancies with each duration/year combination.
Is there evidence that the way the hospital deals with pregnancies involving twins may have changed? Answer the following questions to perform the appropriate statistical test.
Question 1: What is the degrees of freedom for this test?
Question 2: What is the value of the chi-square test statistic? (use 4 decimal places)