Statistical Analysis using Independent Samples t-test

This very common method of statistical analysis allows us to test the difference between two independent means. In layman’s terms, this means we are looking for differences between two groups of participants that are not related. In statistical terms, this means that the scores of the two groups are not correlated.

How is the independent samples t­-test used?

The independent samples t-test can be used when looking for differences between any two groups on a single measure, e.g. differences on SAT scores by gender, differences on GPA by gender, or differences on ACT scores by ethnicity (African American vs. Caucasian).

What types of variables can be used in an independent samples t-test?

There are two variables in an independent samples t-test, an independent variable and a dependent variable. The independent variable is the grouping variable and must be dichotomous or two groups. The dependent variable must be continuous/interval, however, sometimes it’s okay to use ordinal variables, but that is a whole other topic.

What are typical uses of the independent samples t-test?

Often, independent samples t-test are used to look for differences between control and experimental groups. Some research designs employ both an experimental group and a control group with measures before a treatment and after a treatment for both groups. While the statistical test for examining differences within the control group before and after the treatment and within the experimental group before and after the treatment is a dependent samples t-test, the statistical test for examining differences between the control group and the experimental before the treatment and then again after the treatment is an independent samples t-test.

If I am a researcher hoping that my additional math class as a treatment is effective, I am hoping to find that the control and experimental groups are the same pre-treatment, but different post-treatment. Hopefully, my experimental group would have higher math scores post treatment, than my control group. For information on conducting the independent samples t-test in SPSS, please see the information on www.

Statistical Analysis

How do I know what type of statistical analysis to conduct?

Researchers working on studies, theses, and dissertations, often ask this question. Ideally this is a question to ask at the beginning of the research project, rather than the end. It is at this point that research needs should be assessed and hypotheses determined. During the initial stages of planning is the time to involve a statistics consulting firm to help you formulate the basis of your study. There are many things that can influence the type of statistical analysis to use but here are a few important ones:

1. Empirical information (statistical analysis) related to your study

If you are at the point in your study or dissertation that you have begun to consider the type of statistical analysis you need to conduct, then hopefully you have considered the statistical analysis of other researchers in similar studies. It is wise to do this, if only for comparison purposes. However, utilizing the same statistical analysis that has been utilized by other researchers and experts in your field will lend credence to your findings and avoid the difficult, if not embarrassing, task of defending why you chose a different type of statistical analysis.

2. University/College requirements

While I don’t believe it appropriate, many colleges and universities stipulate the type of statistical analysis their dissertation candidates can use. Often, the statistical analysis requirement is the use of multivariate analysis. Make sure you are aware of any of these requirements prior to formulating your research questions and hypothesis.

3. Formulation of the research questions and hypothesis

It is very important to have an idea of the statistical analysis to be used before formulating your research questions, hypothesis, and methodology. The wording of your research questions and hypothesis will determine the type of statistical analysis to be conducted.

· Words like relationship and correlation, tend to correspond with correlational statistical analysis. Sometimes these words also represent regression statistical analysis, but usually correlational statistical analysis.

· Words like predict, affect, and impact tend to correspond with regression statistical analysis, both linear regression and logistic regression.

· Research questions using the difference tend to correspond with t-­tests, both dependent and independent and ANOVAs.

This means you should have an idea of the statistical analysis to be used before crafting your research questions and hypothesis. It is much easier to do this before the proposal is approved than after.

4. Ability of the researcher

While every researcher aspires to change the world, the statistical analysis should fit within the comfort and abilities of the researcher. If you are having difficulty formulating your methodology around statistical analysis with which you are comfortable, it may be wise to consult a statistics consulting firm to help you with the data analysis and statistical analysis. If you have had two or three statistics classes three years ago, you may not want to choose a complex statistical analysis utilizing structural equation modeling or even multivariate analysis. Though a statistics consulting firm will help tremendously in explaining and using complex analysis, you are ultimately the one that will be defending it and explaining it to your committee. Just a reminder, a wise person knows their limitations.

For a customized, confidential help formulating your research questions and hypothesis, and/or conducting your statistical analysis, please call Statistics Solutions Inc. (877) 437-8622 for a free 30 minute consultation .

Where can I find Dissertation Assistance?

Most students secure dissertation assistance in the dissertation process. Let’s face it, the dissertation is new terrain. Statistics Solutions are professional researchers and statisticians providing dissertation assistance in this new terrain. Most students need dissertation assistance with their method section—refining their research questions, selecting the correct data analysis plan, and justifying the sample size.

When you write your research questions, make sure each of the variables in your research questions can be measured, and use language in your questions that relates to the heart of what you want to know. For example, are you looking to examine differences on SAT scores by gender? If so, a t-test is the appropriate statistic to examine differences. Or are you seeking to predict SAT scores from gender? Here a linear regression would be the correct statistical test. You can see that the phrasing of the research question drives the type of analysis: this is the type of dissertation assistance that Statistics Solutions provides.

Frequently, justifying the sample size is dissertation assistance that students look for. Just like the phrasing of the research question drives the statistical test, the statistical test drives how many participants are necessary. Statistics Solutions frequently assists dissertation students daily with sample calculations and sample size equations.

When you get dissertation assistance, get assistance from individuals that have actually completed a dissertation! It only makes sense to get dissertation assistance from those who have personally traveled the dissertation path themselves.

If you have questions and need dissertation assistance, feel free to contact Statistics Solutions for a free 30-min consult. Our phone number is (877) 437-8622, or email us at: www.StatisticsSolutions.com.

Get the dissertation assistance that you need and the very best in finishing your dissertation!

Dissertation Writing

Where do I start with writing my dissertation?

My name is Dr. James Lani, and in this short blog, I hope to demystify aspects of the dissertation writing process, overcome dissertation writing barriers, have you feel confident that you can write your dissertation, and move on with your life.

What is the first step in the dissertation writing process?
The very first step to dissertation writing is overcoming your fear. Yes, the idea of writing a dissertation can be ominous. But here’s a key: your attitude is going to make the difference! For example, have you ever thought something was going to be hard—and then it was? The same principle applies in writing your dissertation writing. When something is new, we can get afraid—and writing a dissertation is no different. First, acknowledge that you made it this far, your almost there, and you can complete this too. I’m suggesting you acknowledge, and then overcome your fear (Yes, thank your fear and move on). Now let’s spend your time thinking and writing!

OK, we’re a bit more empowered, now what?
Obviously, dissertation writing implies you have something to write about—you need a dissertation topic! You don’t need a world changing dissertation topic, just a topic. I don’t agree that it has to be a “large project.” It’s a paper with components—that’s all.

Dissertation topic, dissertation writing, and time management books
Forget all of these dissertation writing books and time management books (heck, if we had enough time to read a book, we’d have already completed method section). Dissertation writing is a task to completed to be sure, but dissertation writing process need not be associated with a study in itself.

How do I write my dissertation?
I’m going to make this very easy. Start with the method section. I’ll tell you, if you can settle on a few research questions and find some survey instruments that can test those research questions, you are almost home. From there we can write the data analysis section (we can help: James@StatisticsSolutions.com; 877-437-8622), and get information on the reliability and validity of the instruments, almost always available from the instruments’ authors. You can then focus on the rationale for doing your study, then focus the lit review on the research variables of interest. This will get you through the proposal.

Dissertation Writing Help
Seek out help to write your dissertation. A company like ours (James@StatisticsSolutions.com; www.statisticssolutions.com) can help you organize your topic and research questions, and help with the dissertation writing process. I hate to confess that our company can organize a method section in one day! How can that be? Because we don’t have the baggage of “it’s tough,” and we’ve been doing it for 16 years. So get the help to move forward with your dissertation writing.

Final thoughts on the dissertation writing process and completing your dissertation
Life is not without bumps on the road, and writing a dissertation is no different. As an old friend once said, let the bumps on the road be your stepping stones rather than stumbling blocks. Get help, get support, get sleep, and if you’re depressed and anxious, get a therapist. Never get defeated, never give up. You can and will complete the dissertation writing process. I sincerely wish you well!
James Lani completed his dissertation in 2003 from Miami University in Oxford Ohio, an APA-approved Ph.D. program in Clinical Psychology. He was blessed with a chair that was tough on his dissertation writing. That toughness has now inspired James to assist literally thousands of students smooth the dissertation writing road, and help students move on with their best lives. His company, StatisticsSolutions.com is based in Clearwater, FL with office opening in New York City, Los Angeles, Atlanta, Austin, Phoenix, and Chicago. He can be reached at James@StatisticsSolutions.com or at 877-437-8622.

What is included in the data analysis plan?

A critical component to theses' and dissertations' method section is the data analysis section or data analysis plan. The data analysis plan clearly identifies the specific statistical techniques (i.e., statistical tests) used to examine the research questions. Often, students get stuck in data analysis, or data analysis plan, because selecting the statistics can vary between parametric and non-parametric statistics. the data analysis plan describes not only the statistics, but the assumptions associated with these statistics. The data analysis plan can be a bit tricky: the specific statistics have to take into consideration the research questions and the type of data that the researcher is collecting(e.g., nominal data, interval data, etc.). A portion of the data analysis plan is to justify why these statistics selected are appropriate for a researcher's hypotheses and research questions. To give you an example for a data analysis plan, a researcher examining differences on an interval level variable (e.g., depression symptom) by gender, an independent sample t-test would be the appropriate statistical technique.

If you have any questions about the data analysis plan or justifying the appropriate statistics in the data analysis, feel free to visit us at www.StatisticsSolutions.com or call us at 877-437-8622. We are experts in writing data analysis and editing data analysis sections.

Chi Square

One of the most common statistical tests we are asked to run at Statistics Solutions is the chi-square, aka Pearson chi-square, cross-tabulation/cross-tab, ect... It seems like there is a lot of confusion about when to use this test and how to use this test. Let’s start out with the “when”.

Chi-square statistical analysis is used when we want to know if there is a relationship between 2 categorical or nominal variables. For example, say I want to know if there is a relationship between males and their level of education. Really, we are looking at a relationship between the variable gender, which is dichotomous (two levels or groups in the variable) with respondents or participants being either male or female, and the variable education, which we’ll say is also dichotomous (high school or below and above high school).

What is the relationship here? We might have hypothesized that there would be a significant relationship between males and education, the nature of which would be men tending to be less educated than women. If our chi-square test is significant - we’ll talk about what makes it significant later – we’ll see some pattern of relationship between these two groups.

Gender * Education Crosstabulation

Count

		Education		Total
		High School or Below	Above High School
Gender	Male	31	25	56
	Female	14	30	44
Total		45	55	100

This is the actual output table we would get if we ran this test. There is no real wrong way to look at the the numbers, since the chi-square is really telling us if the rows are significantly related to the columns.

You can see from the table that 31 participants were male and had an education level of High School or Below and looking at just that column we can see that far more males than females had an education level of High School or Below. There is another number that jumps out at me, and that is the Female row. Notice the 30. Within the Female row or group we could say, 30 had an education level Above High School compared to only 14 with an education level of High School or Below. This is fairly clear, but even more easily seen if we look at the percentages. Let’s look at percentages first within each of the education groups.

Again this is the exact table:

Gender * Education Crosstabulation

			Education		Total
			High School or Below	Above High School
Gender	Male	Count	31	25	56
		% within Education	68.9%	45.5%	56.0%
		% of Total	31.0%	25.0%	56.0%
	Female	Count	14	30	44
		% within Education	31.1%	54.5%	44.0%
		% of Total	14.0%	30.0%	44.0%
Total		Count	45	55	100
		% within Education	100.0%	100.0%	100.0%
		% of Total	45.0%	55.0%	100.0%

This table looks a little confusing, but look a closer look at the names and we can decipher what this means. The numbers of interest are bolded in red. The table shows that 68.9% of the participants/respondents are male and have an education level of High School or Below. You can see that the percentage of males in this education level is much higher than the percentage of females, which is 31.1%. In fact, there are more than twice as many males as females in the High School or Below education level.

What is exploratory factor analysis (EFA)?

Exploratory Factor Analysis is an item-reducing strategy intended to create factor scores. For example, if you have a 100 question survey, you probably don’t have 100 unique constructs/factors. Factor analysis would “boil-down” these 100 questions to perhaps 10 subscales or constructs.

Two important issues in Exploratory Factor Analysis is how many factors there are, and which questions load on (or relate) to that factor. There are several ways to determine the number of factors: scree plot, 70% or more of the variance accounted for, etc. After the number of factors is determined, the questions that go with each factor can be determined by taking your sample size, noting the critical value for a correlation given that sample, and doubling it. If you had 50 observations (participants), the critical value of the correlation at an alpha of .05 is .361; doubling this value equals .722. That is, questions that have a loading of .722 or more would go with that factor.

For more information you can email us at http://www.statisticssolutions.com/ or call us at 877-437-8622.

What does a bivariate correlation indicate?

A correlation, or bivariate correlation, measures the relationship between two variables. The correlation measures the strength of the relationship.

The strength of a correlation ranges from the absolute value from 0 to 1; the closer the correlation is to 1, the stronger the relationship, the closer the correlation is to 0, the weaker the relationship. For example, the relationship between temperature and ice cream cones sold may be .80. This indicates a strong relationship. The direction can be positive or negative. For example, the positive correlation in the ice cream example is positive; as the temperature increase, ice cream cones sold increase. A negative correlation may be found between spending and saving in the bank; as spending increases, saving decrease.

There are other correlations, such as partial correlations, point-biserial correlations.

If you have questions, call us at 877-437-8622 or visit us on line at WWW.StatisticsSolutions.com

What can a dissertation statistical consultant do for me?

A dissertation consultant should have been through the process of a dissertation because we know the challenges of committees and the importance of timely feedback.

Your consultant must be able to clarifying the research questions, assist with selecting the appropriate statistics, select the correct sample size given the statistical analyses selected, conducting the statistics while examining their assumptions and remedies of violations, write-up the results with APA tables, and clearly explain what the finding indicate. Further, you should get continued support!

If you have questions, feel free to contact Statistics Solutions for a free consult. Our phone number is (877) 437-8622 or email us at: www.StatisticsSolutions.com.

The best in finishing your dissertation!

How do I select a statistical consultant?

It only makes sense to hire a company where the consultant has dealt with dissertation committees (i.e., the consulting company have employees who have a doctorate degree) and has expertise in statistics (Ph.D. is preferred). Confirm their credentials—if they say they have a degree from Harvard Department of Statistics—call Harvard’s statistics department top confirm (I have a Ph.D. in Clinical Psychology from an APA-accredited program at Miami University in Oxford, Ohio).

Make sure the company is responsive, patient with answering your questions, and trust your experience with the potential company. Remember, you are the customer!

If you have questions, please feel free to call us at 877.437.8622 or visit our website at http://www.statisticssolutions.com/