You go to your doctor to get a check-up.

A nurse wraps your arm with a pressure cuff and pumps it up to measure your

blood pressure which is recorded as two numbers maybe 114/74. So far, so good.

But what if you want to use that blood pressure reading in a statistical

analysis? You can’t enter 114/74 because it

will be treated like a ratio of 150% We need a

single number that is usable for statistics. For this example, we’re going

to use both Excel and SPSS as we dive deeper into how to solve the tricky

problem of isolating the data that we need computing a new variable with a

formula and then creating a single number called the mean arterial pressure. For this example we’re going to start

with some data in Excel. Now these data come from patient charts and they

represent blood pressure readings for a collection of patients. We’re going to

isolate the parts of the data that we need, and then use a formula to assemble

those parts into a meaningful variable that we can use to measure blood

pressure. We are going to accomplish this in three steps. Step 1: separate the

values in Excel using the LEFT and RIGHT commands.

Step 2: bring that data into SPSS. Step 3: calculate a new variable for MAP

using the formula. Here is why we are starting this process in Excel: I don’t

know of any way to do this in SPSS. In Excel, however, we can use the LEFT and

RIGHT functions to isolate each part of the blood pressure reading. You, of course,

recognize these as blood pressure readings: systolic over diastolic. But

Excel sees them as ratios, like 1.52% We want the systolic

numbers in one column and the diastolic numbers in a second column, so that we

can then use them in the mean arterial pressure formula.=((2*DIA)+SYS)/3 And where did I get this formula? The formula for mean

arterial pressure is in most nursing textbooks or you could find it with a

quick internet search. We will begin by creating some new

columns labeled SYS for systolic and DIA for diastolic.

For the systolic numbers, we will use the LEFT function. The syntax for the left

function is this you first reference the cell that contains the text, followed by

the number of characters. The systolic numbers are the first three numbers on

the left so we would type=LEFT (A2, 3). This creates a cell with the first three numbers on the left end.

Highlight the cell and double-click on the handle to copy it to the remaining

cells. If all of the diastolic numbers are two digits, then the next part is

easy. We simply use the RIGHT function to copy only the rightmost two digits into

the DIA column. This creates a cell with the two numbers on the right end.

Highlight the cell and double click on the handle to copy it to the remaining

cells. In our case however, we have several blood pressure readings with

three diastolic digits. Some have two digits, some have three digits. What can

we do? The solution is to improve our diastolic formula. For the diastolic

numbers we will still use the RIGHT formula, referencing cell A2, but for the

number of values we have Excel return the entire length of A – – everything

before the slash using the SEARCH function. Double click to copy down. LEFT and RIGHT

functions belong in the category of TEXT functions in Excel, meaning that the

result of a LEFT or RIGHT formula is always a text string, even if the

original values were numbers; therefore, these numbers are being read as strings.

So if you try to do the mean arterial pressure calculations in Excel, you will

get an error. That is why at this point I import these values into SPSS. After

import, SPSS will read the numbers as numeric values and import them that way.

But for those of you who are wanting to do this entirely in Excel, you should

wrap the LEFT or RIGHT functions in the VALUE function, which is designed to

convert a string into a number. I am going to save this Excel file to

the desktop, so that I can import it into SPSS. In SPSS I go to File -> Import Data ->

Excel. I go to the Desktop, select the blood pressure file and click Open. I click OK in the import dialog box and

the file opens. Notice that both systolic and diastolic numbers have imported as

scale data. To create the mean arterial pressure, I will use the Compute Variable

function with a formula. Go to Transform ->->Compute Variable. I will create a

variable called MAP, and for the variable label, I will type “Mean Arterial

Pressure”. The formula for MAP is ((2*DIA)+SYS)/3. Click OK. We now have a single number calculated from blood

pressure readings that we can use for analyzing blood pressure among our

respondents.