Correlations

• association

  illustrates the strength and direction of an association between two co-variables.
• scattergram

  correlations are plotted on a scattergram. one co-variable is on the x-axis, the other is on the y-axis.
• what are the three types of correlation?

  positive, negative and zero correlation.
• positive correlation

  co-variables rise or fall together.
• negative correlation

  one co-variable rises and the other falls
• zero correlation

  no relationship between the two variables.
• differences between correlations and experiments

  • in an experiment the researcher manipulates the IV and records the effect on the DV. in a correlation there is no manipulation of variables and so cause and effect cannot be demonstrated.
  • in a correlation the influence of TVs is not controlled, so it may be that a third 'untested' variable is causing the relationship between the co-variables (called an intervening variable)
• strengths of correlations

  • useful starting point for research. by assessing the strength and direction of a relationship, correlations provide a precise measure of how two variables are related. if variables are strongly related it may suggest hypotheses for future research.
  • relatively economical. unlike a lab study, there is no need for a controlled environment and no manipulation of variables is required. correlations are less time-consuming than experiments.
• limitations of correlations

  • no cause and effect. correlations are often presented as causal, e.g. by the media, when they only show how two variables are related. there may be intervening variables that explain the relationship.
  • method used to measure variables may be flawed. for example, the method used to work out an aggression score might be low in reliability (observational categories might have been used). thus would reduce the validity of the correlational study.
• what is an intervening variable?

  a third 'untested' variable that is actually causing the relationship between the two variables.