Statistical Design

Here are a few notes on Statistical Design from class today...

As you design your study it is important to realize that statistical significance is different than practical significance. Your results can be statistically significant, but not practically important.

Determining the Sample size
The following four pieces of information are needed to determine the sample size:

1. Acceptable type on error (alpha) - standard value is .05
   
2. Acceptable type two error (beta) - standard value is .2 (power of .8)
3. Standard deviation - pooled estimate of the standard deviation (sq. rt. of the error mean squared error), includes block effects and covariates
4. Meaningful difference you want to detect

There are various "rules of thumb" that can help you figure this out based on having the above information. For instance, the following is a basic formula that could be used:

n=16/(delta/sigma)^2

where delta is the change in means between the two groups you might be comparing.

Here is another rough regression rule of thumb:

n=15*p

Where p is the number of parameters being used.

Finally, here are some steps to cover when designing your statistical experiments.

Steps in Design

• Question of interest
• Score of inference
• Understand the system
• Response
• Other factors
• Planning
• Statistical anaysis
• Sample size

The often overlooked considerations are very important as new studies are designed.

Tweeting Blog Posts

I just automated the process of making a tweet on Twitter whenever I make a new post on this blog. I set this up using a free service called TwitterFeed.  As a side note, it allows you to do this fo multiple blogs.  

If all goes well, then you will see this post (and all future posts) on my Twitter stream: @smithworx

Things that Make People Happier

Martin Seligman spoke at the BYU forum today in the Marriott Center. Listening from my office I found it quite interesting and relevant, particularly with the doom and gloom ever present in the news. Here are a few tips that he mentioned (they had be learned primarily through controlled experiments):

• Write down three things that went well today and why they went well. (After six months on average you will be happier.)
  
• People that deploy their greatest strengths will be happy.
  
• "Active Constructive Responding" helps marriages succeed.
  
• Do something philanthropic and your whole day go better.
  

Finally, he directed everyone to his Authentic Happiness website for more information on being happy.

Spring Research Conference at BYU

Here are the slides form the presentation that I gave at the Spring Research Conference at BYU last weekend.

Finding Gold in Waste

I first learned about this here, but wanted to share it again.  In short, before you discard all of your junk, you might want to be sure that it is indeed worthless.  In the video below, these guys are finding gold in the sewage.