How to Calculate Relative Risk

Relative risk is a statistical term used to describe the risk of a certain event happening in one group versus another. It is commonly used in epidemiology and evidenced based medicine, where relative risk helps identify the risk of developing a disease after an exposure (i.e. a drug/treatment or an environmental exposure) versus the risk of developing a disease in absence of the exposure. This article will demonstrate how to calculate relative risk.


1. Draw a 2x2 table. A 2x2 table is the basis for many epidemiological calculations.

• Before you can draw a 2x2 table yourself, you must understand the variables:
  • A = The number of people who both had the exposure and developed the disease
  • B = The number of people who had the exposure but did not develop the disease
  • C = The number of people who did not have the exposure but did develop the disease
  • D = The number of people who neither had the exposure nor developed the disease
• Let's do an example 2x2 table.
  • A study looks at 100 smokers and 100 non-smokers, and follows them for development of lung cancer. 

• Right away, we can fill in part of the table. The disease is lung cancer, the exposure is smoking, the total numbers of each group is 100, and the total of all the people in the study is 200.
• At the end of the study, they found that 30 of the smokers and 10 of the non-smokers developed lung cancer. Now we can fill in the rest of the table. 

Since A = the number of people exposed who got the disease (i.e. smokers who got lung cancer), we know this is 30. We can calculate B simply by subtracting A from the total: 100 - 30 = 70. Similarly, C is the number of non-smokers who got lung cancer, which we know is 10, and D = 100 - 10 = 90.

2. Calculate the relative risk using the 2x2 table. The general formula for relative risk, using a 2x2 table, is: 

 

We can calculate relative risk using our example:



Therefore, the relative risk of acquiring lung cancer with smoking is 3.

3. Interpret the results of relative risk.

• If the relative risk = 1, then there is no difference in risk between the two groups.
• If the relative risk is less than 1, then there is less risk in the exposed group relative to the unexposed group.
• If the relative risk is greater than 1 (as in the example), then there is greater risk in the exposed group relative to the unexposed group.

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How to Copy Paste Tab Delimited Text Into Excel

Taking text files and getting them formatted into Excel can be a difficult process. Often, it can be useful to copy-paste from text files into Excel. However, Excel can make this confusing and difficult.



1. Copy-paste a tab delimited text into Excel (likely, this will only show up in the first column).
  
 2. Ensure the column you just pasted is highlighted.
  
3. Open the menu Data-> Text to Columns.

 
4. Select 'Delimited' and click 'Next'. 

 
5. Select 'Tab'. 

 

6. Click 'Finish'.

 

7. Now, you can paste additional tab-delimited text into Excel without needing to apply the Text to Columns function. Instead, they paste into the appropriate   

 
8. Finished. 

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Direct messages on Twitter can be sometimes very annoying if you get many of them. Marking them all as read at once can be a good way of removing them from your view without having to sift through each one.

1. Sign in to your Twitter account. Type in your username and password.

 

 

2. Click on the gear icon. You can find it on the top right of your homepage, to the right of your search bar. 

3. Select "Direct Messages." It's the first option from the top of the drop-down menu. A new window will pop up.

  

 

Alternatively, you can click on 'Me' and press the messages icon.

4. Click on the 'tick' icon. This means that you want to mark the direct messages as 'read'.
 

5. Once you do click on it, click on 'Mark all as read'.

How to Take a Screenshot in Mac OS X

If you need to snap a picture of a funny chat conversation, show an expert an error message on your system, create instructions for performing a task, or even contribute to a wikiHow article, a screenshot is the ideal way to show someone exactly what is on your computer screen. Taking a screenshot on Mac OS X is easy, and there are a variety of simple ways to capture just the image you need.



1. Press Command+Shift+4. Your cursor will turn into a small cross-hair reticle.

2. Click and drag your cursor to highlight the area you'd like to take a picture of. A grayed rectangle should appear where you drag your cursor. If you need to adjust your windows at all, press esc to return to a regular cursor without taking a picture.

3. Let go of the mouse. You should hear a brief camera shutter noise if your computer's sound is turned on. That signals that your screenshot has been taken.

4. Find your screenshot on your desktop. It will be saved as a .png file named "screenshot" labeled with the date and time. Earlier versions of OS X will save it as "Picture #"—for example, if it's the 5th screenshot on your desktop it will be labeled "Picture 5".


5. Use the screenshot. Once you have taken your screenshots, they are ready to be used as you need. You can attach them to an email, upload them to the Web, or even drag them straight into an application such as a word processor.