Explain how one would use qualitative, quantitative, and mixed methodology research design to study lifespan development.

Researchers can use qualitative
research methods such as case studies as a source of
new ideas about behavior, tentative support for a theory, and an evaluation of
therapeutic techniques.  In developmental psychology, case studies might be used to
evaluate long-term progress of a psychological issue pertaining to human development. 
Case studies are useful to a certain extent, but we must remember that they are reported
by biased observers and rely upon subjective
evidence.

Researchers use quantitative
research methods such as correlation studies,
because they are more advantageous than qualitative research.  Because researchers
measure their variables, observe numerous participants, and apply statistical analyses
to their research, they are better able to generalize their data to people beyond the
paritipants in the study.  Additionally, correlation studies can be easily repeated.  A
correlation study might be used to determine whether there is a correlation
(relationship) between reading to your children every night and better school
performance.

Mixed-methodology
research is the most useful and valid form of research, because it uses
both quantitative and qualitative methods to measure information.  Additionally,
mixed-methodology uses a technique called triangulation which evaluates the consistency
of the findings by comparing quantitative and qualitative results to better support the
researcher's conclusions.  This method allows Developmentalists to understand the unique
lives of people while making numerical comparisons to support or disprove
hypotheses.