5/19 2. Causality - cause and effect
This is essentially concerned with showing how things come to be the way they are. To do this we need to identify our variables:
- Independent variable - the variable that is deliberately manipulated by the researcher
- Dependent variable - the variable that is measured to find out the effect of the manipulated (independent) variable
- Control variables - may be potential independent variables, but are held constant during the experiment
So, following on with our example, students are timed whilst searching for information to assess the effectiveness of their searching behaviour, some were given prior search training
- Independent variable = training - manipulate by varying training given to different students
- Dependent = time taken to find information - which we can measure by timing how long to search
- Control = searching behaviour may be affected by previous use, age, educational level, and even time of day. Some of these may be controllable but others may not be, e.g. degree of frustration
So, our experimental (or alternative) hypothesis is that if we give more training it will take less time to search and conversely if we give less training it will take more time to search - we have a cause (training) and effect (time taken). The null hypothesis is that there will be no change or effect.
Independent variables are assumed to have a causal impact on the dependent variable
Wikipedia defines causality as ' a necessary relationship between one event (called cause) and another event (called effect) which is the direct consequence (result) of the first' http://en.wikipedia.org/wiki/Causality
3. Generalizability or external validity
The pursuit of findings that can be generalised beyond the specific research - the degree to which the results of a study or research can be extrapolated to other circumstances.
So, generalizability or external validity involves the extent to which the results of a study can be generalized (applied) beyond the sample to the larger population. In other words, can you apply what you found in your study to other people (population validity) or settings (ecological validity). For example, a study of postgraduate Masters students in a UK university that found one method of teaching statistics was superior to another may not be applicable with first year undergraduate students (population) in an American university (ecological).
4. Reliability or internal validity
Reliability or internal validity is concerned with repeating a piece of research in order to establish the reliability of its findings.
Reliability is the consistency and dependency of a measure. Sometimes it is referred to as the repeatability or the test-retest reliability . This means that a reliable test should produce the same results on successive trials.
