Wednesday, May 29, 2013

APA Heading 3 Doesn't Hang Out by Itself

A lot of people do this:

      Here is my heading 3 just like APA tells me to have it (Really?).
      And here is the beginning of the next paragraph, and I go on thinking that I've correctly used APA's 3rd level heading—but I haven't.

You should do this:

     Here is my heading 3 just like APA tells me to have it. And here is the beginning of my paragraph, and I go on feeling rather smug because this is the right way and I know it.

Here is an illustration straight from the sample paper that the APA editors have kindly provided for us.

Useful Sources about First Person and APA 6th (Or: You and I are not the only ones)

I'm out to change the world about this subject because I'm ridiculously committed to accuracy and clarity in writing--not to mention I don't like being put to sleep by an over-reliance on the passive voice. So if you still have doubts, check out these links:

More from Anovisions on the Subject

More from an APA Editor on the Subject

The Other Post on the Same Subject

Monday, May 27, 2013

The Slaughter of Good Ideas (Warning! A bit crotchety)

I am amazed and saddened by the number of studies out there based on analysis that doesn't fit the data. It's like watching the slaughter of an army of good ideas, a slaughter that could have been avoided if only the messenger hadn't taken a wrong turn.

Every single statistical test is based on assumptions. This means that, when you write your proposal, you need one simple little clause and an extra (rather wordy) sentence for each analysis you plan to do. Instead of writing

"I will analyze the data using a linear regression analysis."

you should write

"I will analyze the data using a linear regression analysis if the data meet the assumptions for that test. If they do not meet the assumptions, then I will either transform the data so that they meet the assumptions or perform an equivalent non-parametric test, a test that is robust to unequal variances, or a test that otherwise fits the data."

"Non-parametric" is short for "test that works even on data that are not normal." And yes, you can quote me.

If you don't have these bits of writing in your proposal and your data doesn't meet the assumptions for your chosen analysis, then you are in trouble. Some committees actually require students to run a test that shouldn't be run simply because they said they would, resulting in the student not being able to answer the research questions. I have seen this happen. You may not be allowed to use the appropriate non-parametric equivalent of your chosen analysis. That means that you won't be able to find an effect that may actually be there. It also means that somewhere down the line, like when the dean's office reviews the dissertation, or when you want to become a famous researcher, someone may take a look at your dissertation and find out that the data didn't meet the requirements for the analysis you did—and disrespect you

So safeguard yourself. If you care about your future career, if you want to play with the big, famous, knowledgeable, ethical researchers out there in the real world, talk about assumptions in your proposal and provide a backup plan in case they are not met. 

Later, I'll provide a list of tests and the assumptions upon which they rest. You can also find such lists if you search the internet for them. 

First Person in APA Style: Can we use it? Yes I can!

Most people think that using the first person is anathema in academic writing and substitute awkward anthropomorphisms ("the study seeks to show..."), passively constructed sentences ("the study was designed to..."), or, worst of all, deceptive sleights of word reminiscent of the Wizard of Oz ("The researcher designed the study to..."). 

The APA 6th edition style guide's editors are practical people who eschew anthropomorphisms, unnecessarily passive wording, and writers who pretend they aren't there. Rather than commit any of these sins of style, just come out with it and say, "I designed the study to accomplish..." or "I selected a sample consisting of..." What you don't want to do is make the study all about you. Don't say, "Next I discovered that the t test was the best approach, and when I saw the results, I decided to ..." This isn't about you. It's about the research—the research that you did. 

So be brave, take a deep breath, and tell it like it is. 

Wednesday, May 15, 2013

Assumptions make an ??? of you and me—or not

Each statistical test rests on assumptions. For example, a t test rests on normality in the underlying population, similar variance in both groups, and independence of both groups.


Okay, here are the steps to take to make sure your t test is valid.

  1. Generate a histogram for the dependent variable (height, weight, or whatever). Does it look relatively normal? Good. Does it look like it comes from a normally distributed underlying population, or do you have prior knowledge or proof in the literature that it does? Also good. Does it look flat or in some other way non-normal? You need to look at another form of the t test that is "robust" to non-normality, or in other words, accurate even though the data are not normal. I'll write about tests of this kind later. 
  2. Provided your histogram was normal, go ahead and run the t test. Among the output tables is one that has a few columns for "Levene's Test." Check the significance of the Levene's test. If p > .10 (Do notice the direction of the sign. This is one of the few tests where having p < .05 is bad. You want a p that is GREATER THAN .05), then you have equal enough variances among the two groups. Either way, SPSS helpfully provides you with the results for two types of t test: one that works if the variances are not equal, and one that works only if the variances are equal. Pick the most appropriate one, and there is the result for your t test. I could go on and on about these two different types of t test, but that wouldn't be practical stats. 
  3. This assumption should probably be #1, but like most people, I don't think about it much. In fact, if you don't have independent groups, your t test might not even work. It's very important. Take the situation where a single teacher is answering survey questions about classrooms with only boys and classrooms with boys and girls. For each question, they slide a bar to a point between "total chaos" and "orderly studious behavior." The two bars are stacked on top of each other, the one for boys-only classrooms first and the one for mixed-gender classrooms second. Can you do a t test comparing mean total answer values for the boys-only classrooms and mean total answer values for the mixed-gender classrooms? Are the two groups (boys vs. boys and girls) independent of each other in this methodology? No. Not at all. They are linked by the fact that the same teacher is answering both questions, and further linked by being presented in a format that encourages comparison between them. Fortunately, you have an option: the paired (or dependent) t test, comparing each teacher's answer for boys with the same teacher's answer for boys and girls. That's what I would use in most situations where the two groups were not independent of each other.
A trick: if you don't have indepence among three or more groups and you had really, really wanted to do an ANOVA, you're out of luck. You have to do several paired t tests, comparing each group with each group. 

So when you write your proposal, do add a clause somewhere to explain that if the assumptions for your chosen method are not met, you will substitute an appropriate equivalent analysis. You will save yourself from numerous headaches.

Please check out our website at for more help.

Monday, May 13, 2013

How many groups? t test vs. ANOVA

The rule is simple, on its face: If you have 3 or more groups that you want to compare for a certain outcome (like height, weight, body mass index, score, depth, or other such continuous or scalar variable), you use the ANOVA. If you have only two groups, or a bunch of groups but you want to compare them by twos, then use a t test.

That simple rule of thumb can save you a lot of time. The information in the next entry will help you hone this idea.