Sample Size and Target Population

The text book approach to determining a sample size is to estimate the expected effect size and then use statistical power analysis software to determine the necessary sample size for a given alpha level (e.g. 0.05) and power (e.g. 0.80) in order to detect the estimated effect size.

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Matching Pre-Post Data Annonymously

When utilizing a pre-test/post-test survey study design, it is necessary to match individual study participant’s pre-test data to their post-test data. Intuition might suggest the researcher only needs the study participants to write their name, email address, social security number or some other personal identifier on their pre/post surveys so they can later be matched.

. . .

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Combined Comparative and Correlational Study Desgin

It is very common for a research study to involve some research questions that are comparative (e.g. t-test, ANOVA) and other research questions that are correlational (e.g. Pearson’s correlation). Sometimes, university committee members challenge the doctoral study to define the study design as one or the other, comparative or correlational, and they won’t accept a combination of both comparative and correlational analyses.

In my opinion, this challenge should never come up because . . .

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All But Dissertation (ABD)

A doctoral student has completed all of their coursework but they have not yet completed their dissertation. There are two types of doctoral candidates that fall into this category:

1) The “just arrived” and anxious to move forward.

2) The “been there for awhile” and think they will never move forward.
While both types might require help to move on, it is the latter that is likely to derive the most benefit from this article and become motivated to complete, perhaps, the most important event in their life . . .

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Summative Scale Scores and Parametric Statistics

Occasionally, doctoral students are challenged on the validity of using parametric statistics to analyze summative scale scores. I’m referring to a scale score that is derived by averaging (or summing) many Likert-type survey questions to measure an underlying construct like “emotional intelligence” for example. So, for example, let’s say . . .

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Ordinal data, continuous data, and statistical tests

Several of my clients, and their committee members have had some misunderstandings about the use of parametric statistics with ordinal data, so I decided to write this article.

Many statistical procedures such as Pearson’s correlation and Linear regression analysis require certain assumptions about the data in order for the procedure to be valid. One of those assumptions . . .

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Why Should I Perform Pearsons Correlation and Multiple Linear Regression Analysis?

Suppose you want to find out if there is a correlation between job satisfaction and the perception of the supervisor’s leadership style among non-supervisory employees. Suppose you use the Multifactor Leadership Style Questionnaire (MLQ) to measure five transformational leadership styles (the MLQ measures other leadership styles too but we don’t need them for this explanation). Let’s call . . .

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Should I use One-tailed or Two-tailed Hypothesis Tests?

One-sided alternative hypotheses are rarely used and I usually discourage their use. The point is, why limit yourself to a one-sided alternative hypothesis? If the results should happen to be statistically significant . . .

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What is the smallest sample size I can use for my study?

This is actually a tougher question than you might think. The text book way to determine a sample size is to conduct a literature review to determine what effect size you are looking for. For example, suppose . . .

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How to Write A Dissertation Proposal – A Statistician’s Viewpoint

As a professional statistician I have helped many hundreds of doctoral students with the statistical aspects of their dissertation proposal. Along the way I have found that many doctoral students struggle with the development of the entire proposal, not just the statistics. This article gives some insight into what I have learned about how to write a doctoral dissertation proposal …

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Recruiting Study Participants

Recruiting participants for a research study can be challenging. I often advise my clients to consider inviting members of a professional association to participate in their survey research. There are many advantages to this approach:

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When Should I Start Working with a Statistician?

I would like to emphasize that the sooner you start working with a statistician during the development of your proposal, the smoother things will go for you. Once you have a topic and you have done some preliminary literature review is an ideal time to start working with a statistician.

So many of my clients come to me only after multiple rewrites of the problem statement, research questions, data analysis plan etc. They could have saved themselves a lot of time, money and frustration by contacting a statistician sooner.

In addition, many of my clients come to me only after they fully approved proposal. Often times, a proposal is accepted even though the statistics are not clearly written and sometimes, their statistics are just plain wrong. This can happen if you don’t have someone with an advanced degree in statistics on your committee. When that happens, I am unable to do the analysis for them unless we first redo the statistics in the methods chapter.

Another thing that happens is, the student comes to me with a fully approved proposal and they want help with the analysis. The statistical aspects of their methodology are correct, but unnecessarily complicated that I am unable to help them due to the scope of the project being so large I could not fit the work into my schedule, nor could I do the work for an affordable price.

These are some of the reasons why you want to work with a statistician early in the development of your proposal.

My Proposal has been accepted, can you analyze my results?

Probably, but many doctoral students do not have an “actual statistician” on their committee. The methodologist on your committee surely has more experience with statistics than your other committee members, but that is very different than having someone with an advanced degree in statistics and 14 years or more of experience as a statistical consultant on your committee. The point is, I have seen many committee-approved dissertation proposals that have research questions that do not lend themselves well to statistical analysis.

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I Tried to Analyze my Data Myself, Can You Review my Results?

I have had a number of doctoral students call me with a question something like this: I purchased the student version of SPSS. I was able to calculate the mean and the frequency and percent for my variables, and I even tried to compare my independent and dependent variables with an ANOVA, but I don’t know if I did it right. Would you please review my work and see if I did it right?

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Testimonials From Past Clients

My name is Steve Creech. I have a Master’s degree in probability and statistics and I have been employed full time as a professional statistician since 1993. I created my own statistical consulting business, Statistically Significant Consulting, LLC, specifically to help doctoral students with the statistical aspects of their dissertation. I offer statistics consulting to doctoral students on a fulltime basis. You can read more about me and my statistical consulting services on my home page: http://www.statisticallysignificantconsulting.com/, or you can contact me by email: steve@statisticallysignificantconsulting.com, or phone: 800-357-0321. Here are some testimonials from past clients who have something they would like to share with others about their experiences working with me.

Were You Advised to Hire a Statistician?

Many of my clients have reported to me that their advisor recommended they hire a statistician to help with their dissertation. I am curious to know how many of you out there have had this happen. In my view, statistical consulting benefits both the doctoral student and the mentor. Often times the mentor has limited experience with statistics.

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How Did you First Go About Handling Your Statistics?

Once you got more heavily into the statistical aspects of your study (e.g. development of your methods chapter), what was the first thing you did? Many of my clients have told me they didn’t even know statisticians existed. They came to me only after many rewrites as a result of criticisms from their committee regarding their statistical considerations. I also have heard comments from clients that they had a statistics class or two several years ago and since have forgotten everything.

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When Did Statistics Start to Become an Issue For You?

At what point during the development of your dissertation did you begin to struggle with statistics? In my view, statistical considerations come into play almost as soon as you have developed a topic. For all practical purposes, a statistical consultant is probably not necessary until you have spent time developing the topic and doing some literature review.

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How Does Statistical Consulting Work?

I have helped hundreds of doctoral students in developing their research questions, hypotheses, survey design, data analysis plan, power analysis and sample size justification, and performing the statistical analysis of their data.

My clients receive a clearly written report that demonstrates how to interpret and report the results “AND” they receive unlimited email and phone support to answer any questions they might have, to ensure that they completely understand their statistics.

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Choosing a Statistical Consultant

In choosing a statistical consultant, ask yourself the following questions:

1) Does my consultant have a graduate degree in statistics?

2) Is statistical consulting for doctoral students their fulltime job, or is this something they do in the evenings and the weekends when they have time?

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Is Dissertation Statistics Consulting Ethical?

When I am asked this question, I like to respond with the following analogy. Surgeons do not usually perform their own anesthesia, because anesthesia is a highly technical and specialized field, and the surgeon would prefer to leave that to an expert. By analogy, most researchers do not perform their own statistical analyses, because statistics is a highly technical and specialized field, and they would prefer to leave the statistics to an expert. So, if writing a dissertation is about learning how to do research, then by working with a statistician, you are gaining real-world experience in how to do research. Continue reading

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