Creating New Variables in JMP Datasets Using Formulas Exercises

Transcription

1 Creating New Variables in JMP Datasets Using Formulas Exercises Exercise 3 Calculate the Difference of Two Columns 1. This Exercise will use the data table Cholesterol. This data table contains the following variables: Clinic (ID number) Gender (1=Male, 2=Female) DOB (Date of birth) Entry_dt (Date of study entry) Height (cm) Weight (kg) Before (Cholesterol measure taken before treatment) After (Cholesterol measure taken after treatment) We want to create a new variable that is the difference of the Before and After cholesterol measurements. 2. Add a new column to the data table Cholesterol. Name the new column Difference (after-before). Its Data Type is Numeric. Its Modeling Type is Continuous. 3. Click Column properties Formula Edit Formula. 4. Within the Formula Editor window: Select After from the table columns list. Within the operator keypad, click on the minus symbol (-). Select Before from the table columns list. Click Apply and OK. 5. Click OK in the Column Info window.

2 6. Save the dataset. Exercise 4 Calculate BMI 1. This exercise will also use the data table Cholesterol. 2. Add a new column to the data table. Use the Cols Add Multiple Columns option to place the column after the Weight (kg) variable. In the Column Info window, name the column BMI and then click Column properties Formula Edit Formula. 3. BMI is calculated as weight(kg) height(m) 2 4. Within the Formula Editor window: Within the operator keypad, click on the division symbol and the following formula will appear Click on the top box (so it s in red) and select Weight (kg) from the table columns list Click on the lower box (so it s in red) and select x y operator keypad. button from the

3 2 In this same lower box, select the division symbol from the operator keypad To get height in meters, divide height (in cm) by 100. Click on the top portion of the lower box and then select Height(cm) from the table columns list. Click on the bottom portion of the lower box and type in Height (cm) Click on Apply and OK and review the new data to ensure that the created data values make sense. REMEMBER: If you make a mistake, click on the box with the error and select the piggy-tail from the operator keypad or key Backspace. 5. Save the dataset.

4 Exercise 5 Using If/Then Statements Numeric Data Suppose we are primarily interested in looking not at the continuous variable BMI but in a categorical (nominal) variable that defines an individual as having a BMI 30 or <30. Thus, we want to create a new column called OBESE in Cholesterol using the Formula Editor to define it as: OBESE = 0 if BMI is <30 1 if BMI is Add a column to the data table. In the Column Info window, name the column OBESE. Change the Modeling Type to Nominal. Click Apply. Click Column properties Formula Edit Formula. 2. In the Formula Editor window, click on Conditional in the functions list and select If and the following formula will appear. If expr then clause else else clause 3. Highlight the lower else clause and click the insert ^ button and the formula will change and appear as follows. If expr then clause else clause expr 4. Highlight each box on the left side of the and then select Comparison from the Functions list and select a<b for the upper box and a >=b for the lower box. If < then clause If >= expr 5. Enter the following information in the blanks

5 If BMI < 30 then clause If BMI >= 30 expr 7. Click on each box on the right side of the and fill in the blanks with the appropriate value for the new variable. If BMI < 30 0 If BMI >= ) Click Apply and OK. 2) Verify the newly created column (OBESE) against the column (BMI) from which it was created. 8. Save the dataset. **Always be careful about how missing values are handled in formulas. ** Exercise 6 Calculating a Time Interval 1. This exercise will use data table Cholesterol. This data table contains the patient s date of birth (DOB) and the date of study entry (Entry_dt). We would like to calculate the time interval, in years, between these two dates. In other words, we would like to calculate the patient s age at study entry. 2. In Cholesterol.JMP, click Cols Add Multiple Columns. Insert the new column after the variable Entry_dt. 3. In the Column Info window, specify the following properties for the column: Change Col Name to Age_Entry. Check that the Data Type is Numeric The Modeling Type should be Continuous. 4. Click Column properties Formula Edit Formula.

6 5. In the Formula Editor, we need to specify the following formula using the following steps: (Entry_dt DOB ) In years(1) Click on Entry_dt in the Table Columns box (left box). Click on the minus sign ( ) in the keypad. Click on DOB in the Table Columns box Click near the minus sign such that the entire formula Entry_dt DOB is included in the red box. Click on the division sign (:) in the keypad. Select Date Time from the Functions (grouped) (right box). Select In Years from the pop-up box. Then type 1 and press enter. This will put the 1 in the parentheses after In Years. If your formula looks like the one above, click Apply. Click OK. 6. Save the dataset.