Pew Research compared respondents to an ordinary 5-day telephone survey with respondents to a 4-month-long rigorous survey designed to generate the highest possible response rate. They were especially interested in identifying any variables for which those who responded to the ordinary survey were different from those who could be reached only by the rigorous survey.
Read each brief report of statistical research, and identify
a) Whether it was an observational study or an experiment.
If it was an observational study, identify (if possible)
b) Whether it was retrospective or prospective.
c) The subjects studied and how they were selected.
d) The parameter of interest.
e) The nature and scope of the conclusion the study can reach.
If it was an experiment, identify (if possible)
b) The subjects studied.
c) The factor(s) in the experiment and the number of levels for each.
d) The number of treatments.
e) The response variable measured.
f) The design (completely randomized, blocked, or matched).
g) Whether it was blind (or double-blind).
h) The nature and scope of the conclusion the experiment can reach.