Answer:
Answers are written in BOLD in the explanation below.
Step-by-step explanation:
(A) The study was done in 1975 but the 825 insulation workers were employed or worked between 1941 and 1944. This makes the study a RETROSPECTIVE study.
There is an exposed group (insulation workers) and an unexposed group (coworkers who did not work with insulation). In addition (an additional reason), the study begins with exposed patients and then unexposed patients. These reasons make it a COHORT study.
This study is also an ANALYTICAL study, as the investigators made a postulation, based on analysis of the number of lung cancer deaths among non-insulation workers and the number of lung cancer deaths among insulation workers.
This is also an ECOLOGICAL study, as study results are applicable only at population level.
(B) This is an EXPERIMENTAL study, as the researcher/investigator seeks new knowledge by selecting groups to derive certain data from; in a step by step manner.
Due to the random selection of subjects (volunteers) and random assignment of them to the two groups, this is a RANDOMIZED TRIAL.
The presence of similar experimental and control groups (all volunteers/subjects have osteoarthritis) is a key feature of RANDOMIZED CONTROLLED TRIAL.
After the selection of subjects, experiment of pain levels was conducted for some months (up to a year). This makes the study a PROSPECTIVE study because there was follow-up on the groups, to see who develops the outcome of interest.
The fact that there was no experimental report after 9 and 12 months of follow-up is another key feature of the RCT because in a RCT, the investigator often faces issues like dropout and noncompliance of subjects.
(C) This is a COMMUNITY TRIAL study because two cities/communities are experimented on.
This is also an EXPERIMENTAL study. The fact that both cities have similar demographic profiles and air pollution levels confirms a key feature of experimental studies. There is a 2-year follow-up. This is another reason why the study is experimental and PROSPECTIVE.
(D) This is an OBSERVATIONAL study. This is because already available data was collected and simply looked upon or observed, to know if chewing tobacco was a significant risk factor for stomach cancer.
The data is historical data, hence this is a RETROSPECTIVE study.
This is also a CROSS-SECTIONAL study because it is observational in nature and it gives characteristics of subjects at a single point in time, not over a period of time. It does not have a follow-up period and cannot provide cause-effect relationship between variables.
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