Analysis of Covariance essay

Analysis of Covariance (ANOVA) Custom Essay

Analysis of Covariance. Up to this point, you have been learning about the effects of various grouping (or independent) variables, such as gender, on an outcome (the dependent variable). In the simple ANOVA design, you assume that only one thing� the independent variable� is affecting the outcome.

In many cases, however, there are several factors that can affect an outcome. These factors can vary across people and situations. For example, mood, level of sleep, and effort are examples of variables that may vary individually and also affect an outcome variable (such as academic achievement). The question is how to account for the effects of these variables (called covariates) statistically.

This week, you will learn how to use analysis of covariance to answer these kinds of questions.

Learning Outcomes

By the end of this week, you will be able to (for ANCOVA):

� State underlying assumptions

� Determine whether assumptions have been met

� Propose alternatives if assumptions are not met

� State null and alternative hypotheses

� Analyze data using IBM SPSS Statistics

� Interpret and report the results with IBM SPSS Statistics, including effect size

� Describe sample size

� Report results in APA format

� Define covariate and provide examples of common covariates associated with your area of research

Application

ANCOVA

As you have learned this week, ANCOVA can be a valuable tool in research design. For this Application, you will use ANCOVA to analyze data from a research study.

To prepare for this Application:

� Review Chapter 12 of the Field text for a description of the analysis of covariance and an example of conducting an analysis of covariance using PASW.

� Review Chapter 5 from the APA manual, “Displaying Results.”

� Review the media about conducting an ANCOVA.

� Read the research study below.

RESEARCH STUDY:

Stalking is a very disruptive and upsetting experience in which someone (the stalker) constantly harasses or obsesses about another person. Stalking can take many forms, from sending intensely disturbing letters to literally following you around in the places where you live and socialize. A psychologist decides to try two different therapies on people who reported a history of stalking and reported currently exhibiting stalking behaviors (25 stalkers in each group; this is the Group variable in the data set Stalker.sav). With those in group one, the psychologist used a cognitive-behavioral approach. With those in the second group, she used a psychodynamic approach. At the end of 3 months, the psychologist asked the clients to report on the number of hours each week they engaged in stalking-type behaviors (this variable is called Stalk2 in the data set). The psychologist understands about covariance and believes that success of the therapy will likely depend on how bad the behavior was to begin with, so she asked the clients to report at their first session the number of hours that the client engaged in stalking-type behaviors (this variable is called Stalk1 in the data set).

The assignment: Using the Statistic_Assignment_Template enclosed do the followings:

Complete Smart Alex’s Task #1 on p. 505 to perform an ANCOVA using the Stalker.sav dataset from the Field text. You can follow the steps outlined in the example in the text beginning on page 489, and analyze the effect of the therapies on stalking-type behaviors after therapy ended while controlling for initial number of hours of stalking-type behaviors.

Report your findings in APA format according to the guidelines in the IBM SPSS Statistics Application Assignment Guidelines handout. The final document should be 2�3 pages long.

Resources

SKIP TO COURSE MENUSKIP TO TOP FRAME TABS

Access Resources

Required Resources

� Course Text: Discovering Statistics Using IBM SPSS Statistics

�

o Chapter 12, “Analysis of Covariance, ANCOVA (GLM 2)”

In this chapter, you will learn about assumptions and issues in ANCOVA, conducting ANCOVA on IBM SPSS Statistics, interpreting the output of ANCOVA, and ANCOVA as a multiple regression.

� Website: Trochim, W.M.K. (2006). Covariance designs. Retrieved from https://www.socialresearchmethods.net/kb/expcov.php

This website provides a description of covariance and explains its functions.

� Handout: Statistics Application Evaluation Criteria (Word document)

This handout will guide you in completing and submitting your ANCOVA Application Assignment for this week.

� Software: IBM SPSS Statistics Standard GradPack (current version). Available in Windows and Macintosh versions. Please refer to the IBM SPSS Software area on the left navigation bar for more information on how to install, register, and license this software.

You will use this software to complete this week’s Application Assignment.

� Media:

o Analysis of Covariance � Conceptual (Adobe Captivate)

Dr. Jennifer Morrow explains the conceptual framework of an analysis of covariance. This Flash-based demonstration will open in a new window.

(Transcript for Analysis of Covariance � Conceptual)

o Analysis of Covariance � Applied (Adobe Captivate)

Dr. Jennifer Morrow provides an example of the analysis of covariance using IBM SPSS Statistics. This Flash-based demonstration will open in a new window.

(Transcript for Analysis of Covariance � Applied)

Research Toolkit

Research Design

� Website: Web Center for Social Research Methods

https://www.socialresearchmethods.net

This website is for people involved in applied social research and evaluation. You will find several resources and links to other locations on the web that deal in applied social research methods.

� Website: Cengage Research Methods Workshops

https://www.wadsworth.com/psychology_d/templates/student_resources/workshops/resch_wrk.html

This website offers many useful workshop topics such as experimental methods, reliability and validity, surveys, sampling methods, ethical issues, and evaluating published research.

Statistics and SPSS

� Website: SPSS Student Resource Center

https://www-01.ibm.com/software/analytics/spss/support/techsupport.html

The SPSS student support site provides a knowledgebase and allows students to request assistance from SPSS Technical Support staff. Since this site is produced and maintained by the creators of the PASW software, it is the best place to go when you have a question about the software.

� Website: UCLA’s ‘What Statistical Analysis Should I Use?’ Table

https://www.ats.ucla.edu/stat/mult_pkg/whatstat/default.htm

This statistics table shows general guidelines for choosing a statistical analysis, and links showing how to do such tests using SAS, Stata and PASW. This is a good place to go if you are not sure which statistical test would best answer the research question you have.

� Website: Statistics Hell

https://www.statisticshell.com/html/apf.html

This site is Andy Field’s (the author of the main course text) online statistics resource. This site provides additional explanations beyond the textbook and more examples. This is the best place to go when you are confused about how to do a particular test.

� Website: Cengage Statistics Workshops

https://www.wadsworth.com/psychology_d/templates/student_resources/workshops/stats_wrk.html

This website offers many useful workshop topics such as experimental methods, ethical issues, and evaluating published research.

Optional Resources

� Text: Using Multivariate Statistics

�

o Chapter 6, “Analysis of Covariance”

This text offers another explanation of the analysis of covariance and goes into more depth regarding the statistical background of the test.

� Text: Publication Manual of the American Psychological Association

o Chapter 5, “Displaying Results”

� Media: Data Cleaning and Dealing with Assumptions (Adobe Captivate)

Dr. Jennifer Morrow explains the assumptions surrounding many of the tests you will study and explains ways that you can manage data that violates these assumptions. This Flash-based demonstration will open in a new window.

� Website: Research Methods Knowledge Base

https://www.socialresearchmethods.net/kb/statcov.php

This is where your introduction goes. Just 2-3 sentences.

Underlying Assumptions of Statistical Test

Write about the assumptions that must be met for this statistical test to be appropriate for your data and for the questions you are trying to answer (see text and companion website).

Also, write about if those assumptions are met or not. If not, what other statistical analyses will you have to do (if applicable).

Research Question

Write your one sentence research question here.

Hypotheses

Null Hypothesis (H0): Write your null hypothesis here.

Alternative Hypothesis (HA): Write your alternative hypothesis here.

**You may have more than one set of these.

Variables

Independent Variables (IV): List your independent variables here as well as how they are coded (values) in your dataset.

Dependent Variables (IV): List your dependent variables here as well as how they are coded (values) in your dataset.

Results

Write your results section here. Please use the exemplars that have been provided (do not copy) and also the text and companion website to help you construct this section.

You need to have an APA formatted table of data in each statistics assignment. This does not mean pasting a table from the SPSS output into your paper. You will not get credit for this. You need to look at table examples from the 6th Edition APA manual and construct and label the table appropriately. Your table should be placed in your narrative where you are talking about the data so that the reader can find it easily. You need to explain the data in the table. Do not just point the reader to the table as they will not necessarily know how to interpret the data if you do not explain it.

In addition, you need to tell the reader if you will reject or accept the null hypothesis and why (based on the data).

Computation of Sample Size

You need to compute the appropriate sample size that is needed for this statistical test based on the type of test, number of variables, desired effect size, 80% power, and alpha of .05. Use G*power or other sample size calculator to do this and explain how you calculated it as well as the sample size you arrived at.

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