Techniques of research control: -Extraneous variables (confounding) are: The variables which could have an unwanted effect on the dependent variable under investigation. (Kind of independent variable). -Extraneous variables: that have irrelevant association with the dependent variable and that can confound the testing of the research hypothesis.

Types of extraneous variables: 1.External factors: stemming from the research situation. 2.Intrinsic factors : are the characteristics of the subjects of the study e.g. age, sex, prior occupation---etc--

Controlling external factors: 1.Achieve constancy of conditions for the collection of data. 2.Ensure the constancy of time 3.Maintaining constancy in the communications to the subjects and in the treatment itself.

-Randomization: -Randomize when over possible 2. Homogeneity -The limitation of this approach, that the research findings can be generalized to the type of subjects who participated in the study. 3. Blocking -Blocking variable: cannot be manipulated by the researcher.

4. Matching Limitations of matching. 1.To match effectively, the research must know in advance what the relevant extraneous variables are. 2.After tow or there variables. It often becomes impossible to match adequately. 5. Analysis of covariance : through statistical analysis

Internal and external validity.  Internal validity: -Refer to the extent to which it is possible to make, an inference that the independent variable is truly influencing the dependent variable.

Threats to internal validity: 1.History: The occurrence of events that take place concurrently with the independent variable that can affect the dependent variables of interest. 2.Selection: encompasses biases resulting from not assigned individuals randomly to groups, (the groups are not equivalent),

3.Maturation: refers to processes occurring within the subjects during the course of the study as a result of time (e.g. growth, Fatigue) rather than as a result of the independent variable. 4.Mortality: refers to the differential loss of subjects from comparison groups. The loss of subjects during the course of a study (subject attrition). External validity: refers to the generalizability of the research findings to other settings or samples.

Guidelines for critiquing research designs. 1.Given the nature of the research question, what type of design is most appropriate? How much flexibility does the research question require, and how much structure is needed? 2.Does the design involve an experimental intervention? Was the full nature of the intervention described in detail?

3.If there is an intervention, was a true experimental, quasi- experimental, or preexperimental design used? Should a more rigouous design is have been used? 4. If the design is nonexperimental, what is the reason that the researcher decided not to manipulate the independent variable? Was this decision appropriate?

5. How many times were data collected or observations recorded? Is this number appropriate, given the research question? 6.What types of comparisons are specified in the research design (e. g. before and after, the use of one or more comparison group)? Are theses shedding light on the relationship between the independent and dependent variables?

7. If the research design does not call for any comparisons, what difficulties does this pose for understanding the results? 8. What procedures, if any, did the research use to control external (situational) factors? Were these procedures appropriate and adequate? 9. What procedures, if any, did the researcher use to control extraneous subject characteristics? Were these procedures appropriate and adequate?

10. To what extent did the design enhance the internal validity of the study? What types of alternative explanation must be considered, given the design that was used? 11. To what extent did the design enhance the external validity of the study? Can the design be criticized for its artificiality or praised for its realism?

12. Does the research design enable the researcher to draw causal inferences about the relationships among research variables? 13. What are the major limitations of the design used ? Are these limitations acknowledged by the researcher and taken into consideration in interpreting the results?