Experimental
Designed to demonstrate unambiguous cause-and-effect relationship between variables |
Determines if there is an effect/outcome of some form of treatment(s) using random assignment of subjects to treatment and control groups. Includes a manipulation of an independent variable to determine its effects |
- Two or more equivalent groups to receive one or more treatments and a control group
- Random assignment of subjects to each of the groups
- Standardization of all aspects of research procedures employed to ensure conditions are the same for all participants (i.e. the control for all variables other than the manipulated variable)
- Conducted with rigorous control with clearly defined treatments
- Categorical independent variables and interval or ratio level dependent variables
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Quasi-experimental
Designed to demonstrate cause-and-effect relationship between variables. Does not meet all requirements of an experimental design, thus cannot produce an unambiguous cause-and-effect explanation. |
Determines if there is an effect/outcome of some form of treatment(s) using pre-existing groups of subjects assigned to treatment and control groups |
- Two or more nearly-equivalent groups to receive one or more treatments and a control group
- Typically no random assignment -participants are in pre-existing groups or groups that are naturally formed
- Inclusion of participants in the control or treatment group is determined by conditions beyond the control of the researcher
- Conducted with similar rigor and control as experimental studies with clearly defined treatments
- Requires categorical independent variables and interval or ratio level dependent variables
- Design contains a confounding variable or factor that prevents the research from obtaining an absolute cause-and-effect answer
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Non-Experimental
Attempts to demonstrate associative relationships between variables but does not attempt to produce an unambiguous cause and effect explanation. |
Descriptive(Survey) |
Describes the opinions, attitudes, or trends of a population numerically |
- Provides a description of individual variables but not concerned with the relationship between variables
- Uses a process of surveying a sample to generalize to the population
- Research may be longitudinal or cross-sectional
- Returned sample should be hundreds or thousands of surveys in order to generalize to the population
- Requires at least ordinal or interval level variables
- Could also be classified as qualitative descriptive depending on the design and collected data
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| Correlational |
Determines if there is an empirical relationship between two or more variables on a single group of participants with the intent of predicting or defining a relationship |
- Observes relationships between variables in a naturally occurring setting.
- Includes two or more variables that can be measured quantitatively
- Valid approaches to data collection such as validated surveys or databases
- There is a theoretical or logical explanation that can be used to predict a correlation
- Requires ordinal or interval level data for variables of interest
- Variables should not or cannot be manipulated
- Could also be a quasi-experimental study if designed as such
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Causal
Comparative |
Determines the causes of differences that already exist between or within two or more groups on two or more variables |
- Identify one or more groups that serve as independent variable
- Define the dependent variable on which the groups will be compared
- Requires at least one categorical variable and ordinal or interval level dependent variables
- Select sample groups that are as homogeneous as possible
- Could also be a quasi-experimental study if designed as such
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| Qualitative descriptive |
A relatively simple phenomenon is described |
- Does not clearly fit into one of the other designs
- Phenomenon has been clearly defined
- Uses two forms of qualitative data collection (typically, interviews a minimum of 15, and may use a second form of data collection such as field notes or questionnaires.
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| Phenomenology |
The essence of a “lived” experiences described by the participants who experienced them are synthesized to describe the phenomenon (from philosophy and psychology) |
- Phenomenon has been defined to be a “lived” experience and focuses on how the participants find those experiences to be meaningful. Participants must have an experience in common, such as experiencing the death of a child, or living with cancer.
- Sample has to have the experience in common
- Focus is on the meaning and description the sample makes of the experience. Must be able to deal with emotional reactions.
- Reality will be the described phenomenon that results from a conscious experience
- In-depth interviews are the primary data collection tool, but may use two forms of qualitative data collection (typically 10-15 in-depth interviews); may use essays or other reflective processes); researcher needs to make detailed field notes following each interview
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| Narrative |
Stories are told by the participants in an interactive fashion with the researcher with the intent of creating a unified narrative or story that describes or explains a life episode (from humanities) |
- Phenomenon is defined as a story of an event which will be better understood including causality and relationships
- Typically uses in-depth interactive interviews with 8-12 individuals who are telling “their individual story”
- May use other story-telling techniques such as creating timelines of events, etc.
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| Case Study |
An in-depth analysis of a one or more cases which can be a process, program, activity, city event, or person, using a number of data collection approaches (from business) |
- Phenomenon is defined as a process, program, activity, city event, or person studied over a specified time period, which is analyzed
- Three to five sources of data (forms of data collection) realize triangulation and depth of analysis
- May include both qualitative and quantitative data collection and analysis.
- A multi-case study may include up to 10 cases
- Typically includes focus groups/interviews with 5 to 15 individuals, and may include observations, document collection, and/or additional forms of data collection
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| Grounded Theory |
A theory or model is developed to describe the phenomenon as a concept, process, interactions, components, or actions (from sociology) |
- A theory or model is developed to describe the phenomenon
- Involves multiple stages of collecting data often using multiple approaches and multiple groups
- Typically includes iterative interviews, observations, document collection, and questionnaires with various groups. Data are collected until saturation is achieved, denoting lengthy periods of time in the field.
- May include both qualitative as well as quantitative data collection and analysis.
- Typically includes collecting a large volume of data either by larger samples or repeated (iterative) collection from individuals.
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