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© Chad Baker/Getty Images © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Chapter © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION 6 © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Quantitative Research Designs: Experimental, Quasi-Experimental, © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC and Descriptive NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Chapter Outline © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC ▶ Introduction ▶ Descriptive Quantitative Designs NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION ▶ Experimental Study Designs ▶ Additional Types of Designs ▶ Quasi-Experimental Designs ▶ Researcher Interview: Intervention Research, Dr. Leslie Cunningham-Sabo, PhD, RDN © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC learning OutCOmes NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION ▶ Discuss five considerations when planning a ▶ Discuss the advantages and disadvantages of research design. various quasi-experimental designs. ▶ Explain the three essential components of ▶ Compare and contrast the descriptive cross- experimental designs, and compare and sectional, repeated cross-sectional, comparative, © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC contrast the following experimental designs: and descriptive correlational designs. NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION randomized controlled trials, crossover, factorial, ▶ Discuss the advantages and disadvantages of and Solomon four group designs. various descriptive designs. ▶ Discuss the advantages and disadvantages of ▶ Read a research study and identify the design various experimental designs. used and analyze study results. ▶ Compare and contrast the nonequivalent © Jones & Bartlett Learning, LLC▶ © Jones & Bartlett Learning, LLC control group and interrupted time series Distinguish between secondary data analysis NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION designs. and secondary research. intrOduCtiOn © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Designing a research study requires making a number of decisions on the steps you will take to answer your research question(s). Like an architect, you need to prepare a blueprint for your project. If you have ever met with an architect before, you know that © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC 155 NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION 9781284126464_CH06_PASS02.indd 155 12/01/17 2:53 pm © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC 156 Chapter 6: Quantitative Research Designs: Experimental, Quasi-Experimental, and Descriptive NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION the process usually starts with a lot of questions. Research design is no different. The following questions address a number of key design features that must be considered. © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC 1. What is the research question? Will there be an intervention? Testing the effects of an NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION intervention is the hallmark of experimental and quasi-experimental research. If there is an intervention with human participants, the researcher will assign participants to be exposed to the independent variable, such as a modified diet or nutrient supplement, or be part of the control group. Experimental and quasi- experimental designs are used to test a hypothesis. © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC 2. Instead of an intervention, will researchers observe study participants and take measure- NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION ments? For example, researchers might observe a group over a longer period of time to see if exposure to certain factors (such as a diet high in fruits and vegetables) affects their risk of disease. This type of design is called a cohort study design. It is commonly used in the field of epidemiology, a discipline within public health that looks at the rates of health-related states (such as disease) in dif- © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC ferent groups of people and why they occur, and then looks at how this informa- NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION tion can be used to control health problems. Study designs used in epidemiology are discussed in Chapter 7. 3. What are the variables? What comparisons are going to be made between or within groups? Comparisons are needed to examine relationships between the indepen- dent and the dependent variable. © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC 4. When and how often will data be collected or measurements taken? Many experimental NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION studies measure the dependent variable at least before and after the intervention. Weight loss studies, for example, often take measurements for a year or more to see whether participants kept the weight off. Data may be collected at just one point in time, such as in a cross-sectional study, or more frequently. In a longitudinal study, participants are observed and measurements are taken over © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC a long period of time. Longitudinal studies either go forward in time (prospec- NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION tive) or backward in time (retrospective). 5. What will the setting be for the study? The setting could be a hospital, community center, or other location. Some studies use multiple sites. 6. In an intervention study with at least two groups, will the participants be randomly assigned to a group? True experimental research involves random assignment to groups © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC so participants each have an equal chance of receiving any of the treatments (including no treatment) under study. Quasi-experimental research does not NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION have randomization of participants to groups. 7. In a human intervention study, will participants, researchers, and staff be blinded from knowing to which group a participant was assigned? Blinding helps to prevent or minimize sources of bias, such as expectation bias. Expectation bias is when © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC researchers’ expectations of what they believe the study results should be get in the way of accurately taking measurements and reporting results. NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION 8. What controls will be put in place to reduce the influence of extraneous variables? Extra- neous variables are factors outside of the variables being studied that might influence the outcome of a study and cause incorrect conclusions. A good quan- titative design identifies and rules out as many of these competing explanations © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC as possible. NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION A good research design helps you answer the research question while effectively reducing threats to design validity. Quantitative research designs are often used to look at causal relationships, but they can also be used to look at associations or relationship between variables. Quantitative research studies can be placed into one of five categories, although some categories do vary © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION 9781284126464_CH06_PASS02.indd 156 12/01/17 2:53 pm © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Experimental Study Designs 157 NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION a bit from book to book. First are experimental designs with an intervention, control group, and randomization of participants into groups. Next are quasi-experimental designs with an intervention but no randomization. Descriptive designs do not have © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC an intervention or treatment and are considered nonexperimental. They usually aim to NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION provide information about relevant variables but do not test hypotheses. Good descrip- tive studies provoke the “why” questions of analytic (cause-and-effect) research. Two additional categories are epidemiologic and predictive correlational designs. When you read about designs in this chapter, examples of studies are given to illus- trate the design. The examples include some discussion of the results of statistical tests, © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC as well as sample tables from the studies. In a quantitative study, statistics are often used NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION to answer one of these questions: 1. Is there a difference among the groups? Example: “LA Sprouts: A Garden-Based Nutrition Intervention Pilot Pro- gram Influences Motivation and Preferences for Fruits and Vegetables in Latino © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Youth” ( Journal of the Academy of Nutrition and Dietetics , 2012) 2. Is there an association or relationship among the variables? NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Example: “Preventable Incidence and Mortality of Carcinoma Associated With Lifestyle Factors Among White Adults in the United States” ( JAMA Oncology , 2016) You can often tell from the title of an article whether the study is looking at differences © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC among groups or an association among variables. NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Experimental and quasi-experimental designs have an intervention, so they involve questions about differences—often the difference between an outcome measured in the experimental and control groups. Correlational studies look at associations. Table 6.1 shows examples of statistics that may be used to answer these two questions. © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC TIP NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION When you read a study, first read the abstract to determine whether there is an intervention. If so, the study is either experimental or quasi-experimental. If not, the study will fit into one of the other categories. If you see the word “association” in the title, the study is likely to be a descriptive, epidemiological, © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC or predictive correlation design. NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION experimental study designs © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC To be considered an experimental design, the following must be present. NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION 1. An intervention or treatment . The researcher manipulates the independent variable by, for example, requiring the intervention group to eat a diet that has been modified, take a supplement containing a nutrient or phytochemical, or take part in an educational program. 2. Control for extraneous variables . Various control techniques, such as randomiza- © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC tion and having a control group, are used. Having a control group allows the NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION researcher to compare and evaluate the performance of the experimental group on the outcome (dependent) variable. 3. Randomization . The researcher randomly assigns each participant to a group so that each person has an equal chance of being in either group. This removes the problem of selection bias so that comparable, balanced groups of similar size are © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION 9781284126464_CH06_PASS02.indd 157 12/01/17 2:53 pm © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC 158 Chapter 6: Quantitative Research Designs: Experimental, Quasi-Experimental, and Descriptive NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Table 6.1 Statistics That Look at Differences and Statistics That Look at Associations Statistics That Look at Differences © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Measurement NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Test level of dependent Name statistic Purpose Number of groups variable Independent samples t To test the difference between 2 Interval/ratio t-test the means of two independent © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC groups. NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Paired samples t-test t To test the difference between 2 Interval/ratio (or dependent t-test) the means from two paired groups (such as before-and- after observations on the same © Jones & Bartlett Learning, LLCsubject). © Jones & Bartlett Learning, LLC One-way analysis of F To test the difference among More than two Interval/ratio NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION variance (ANOVA) means of more than two groups independent groups for one independent variable (with more than one level). Two-way analysis of F To test the difference among More than two Interval/ratio © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC variance (ANOVA) means for two independent groups NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION variables, of which each can have multiple levels. Repeated measures F To test the difference among One group Interval/ratio ANOVA (one-way three or more means in the within-subjects) same group over time. (Extended © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC design of dependent samples NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION t-test). Chi-square χ2 To analyze nominal and ordinal Two or more groups Nominal/Ordinal data to find differences between groups. Statistics That Look at Associations © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Measurement Test level of dependent Name statistic Purpose variable Pearson product- r To measure the strength and direction of the relationship Interval/ratio moment correlation between two variables. © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Spearman rank- ρ To measure the strength and direction of the relationship Ordinal, interval, or NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION order correlation between two variables. (Nonparametric version of ratio Pearson product-moment correlation) Linear regression To predict the value of a dependent variable and Interval/ratio measure the size of the effect of the independent © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC variable on a dependent variable while controlling for covariates. NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Logistic regression Same as linear regression; used when dependent value Binary/dichotomous is binary. © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION 9781284126464_CH06_PASS02.indd 158 12/01/17 2:53 pm
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