Directionality Problem – A problem encountered in correlational studies; the researchers find a relationship between two variables, but they cannot determine which variable may have caused changes in the other variable. Third Variable Problem – A problem that occurs when the researcher cannot directly manipulate variables; as a result, the researcher cannot be confident that another, unmeasured variable is not the actual cause of differences in thevariables of interest. Components of Experimental Research•Independent variable- The variable that gets manipulatedDependent variable - The variable that gets measured. “depends” on the independent variable •Experimental group– Treatment groups; the participants in a study that receive the intervention. •Control group– A comparison group; the participants in a study that receive no intervention or receive an intervention that is unrelated to the independent variable being investigated. Problems with Experimental Research•Confounds- Anything that affects a dependent variable and may unintentionally vary between the experimental conditions of a study.•Sample– A subset of a population. •Selection bias- In an experiment, unintended differences between the participants in different groups. –How to correct sample issues? •Random samples•Random assignment- Placing research participants into the conditions of an experiment in such a way that each participanthas an equal chance of being assigned to any level of the independent variable. Good Research Requires•Construct validity– The extent to which variables measure what they are supposed to measure. •External validity– The degree to which the findings of an experiment can be generalized outside the laboratory. •Internal validity– The extent to which the data collected in a study address the research hypothesis in the way intended. •Reliability– The extent to which a measure is stable and consistent over time in similar conditions. •Accuracy– The extent to which an experimental measure is free from error. Analyzing Data•Descriptive statistics:–Measures of central tendency•Mean– A measure of central tendency that is the arithmetic average of a set of numbers. •Median– A measure of central tendency that is the value in a set of numbers that falls exactly halfway between the lowest
and highest values. •Mode - A measure of central tendency that is the most frequentscore or value in a set of numbers. –Variability – In a set of numbers, how widely dispersed the values are from each other and from the mean•Standard deviation– A statistical measure of how far away each value is, on average, from the mean•Range– The difference between the lowest and highest number in a set of numbers.