Sometimes we want to compare the spread of a distribution to its mean. This can be useful when we want to see which of two or more distributions varies “more” after accounting for the level of the distribution. For example, if we had data on students’ SAT scores and high school grade point averages, it wouldn’t be meaningful to compare the standard deviations – because SAT scores are so much higher. We can use the CV to do this.
You’re about to do some research. You’ve got an idea in your field and you hope to turn it into a grant or an article or a dissertation. Right now, you may not know exactly how you want to work with the idea. It’s just a thought.
How can a statistician help you?
At this early stage, the consultant may be able to suggest novel ways of testing your idea, using analytic methods you’ve never heard of. Then, the statistical consultant will be able to help you plan a sample size and a sampling strategy, write up a methods section and start gathering and recording data in a sensible way.
After you gather data, your statistical consultant will be able to help you analyze the data and understand it, using methods that are appropriate rather than just some method you learned in your two statistics courses.
For instance, if you have a dependent variable and one or more independent variables you may want some sort of regression. But is it
But maybe you don’t need regression at all; or maybe you need a multilevel model. Perhaps factor analysis or principal component analysis or cluster analysis or multidimensional scaling will be vital to answering your research question.
Your statistical consultant will be able to help you figure it out.
Are you writing a dissertation?
Congratulations! You’ve gotten through undergraduate education, graduate courses, comprehensive exams and now …. THE DISSERTATION!
You’re an expert on your subject. By the end of your dissertation, you will surely be very expert on your subject, whether it’s in the field of psychology, sociology, education, social work, economics or some other field. But, in these fields and many others, nearly all dissertations involve statistics. And you may not be expert in that. I am. You may hate statistics. I like it. Read more!
On this site I have written quite a lot about regression analysis.
But what is regression analysis?
Briefly, regression analysis is a set of methods for relating dependent variables to independent variables. In the vast majority of regressions there is one dependent variable and any number of independent variables. There are a lot of types of regression analysis. But, you may ask
What is regression analysis for?
The main thing that makes regression analysis special is the idea of controlling for other variables. The mathematics behind this are interesting to geeks like me, but the basic idea is that of holding other variables constant. It is a way of looking at the relationship between the dependent variable and each independent variable while holding the values of the other independent variables constant.
“OK”, you say
But what is regression analysis used for?
And the answer is: Almost everything!
How do voting preferences relate to sex?
How do college grades relate to age?
How does income relate to age, sex, ethnicity and race?
How does the likelihood of getting cancer relate to smoking?
People often transform their variables. There are two sorts of transformation: One is to simply multiply all the values by a constant. This does not affect the relationships among the variables and, properly done, it will make the output easier for humans to interpret. We measure human height in centimeters (or maybe meters), not kilometers, but the results are the same. In my view, people often fail to do this type of transformation when they ought to: e.g. they will leave “income” in dollars when thousands of dollars makes more sense.
The other sort of transformation is when we take logs or square roots or some other power of the variable. This does affect the relationships among variable and, in my view, people do it too much.
This sort of transformation should be done for substantive reasons, not statistical ones. Read more!