Final answer:
Research methods vary in application: secondary analysis is cost-effective, field research offers qualitative depth, experiments establish causality, and triangulation enhances research validity.
Step-by-step explanation:
Research methods such as secondary analysis of existing data, field research, experiments, and triangulation vastly differ in their approach and application. Secondary analysis capitalizes on pre-existing data, making it cost-effective but limiting in control over how data was collected. Field research involves direct observation or interaction within the subject's natural environment, offering rich qualitative data but with limited ability to generalize findings. Experiments enable researchers to manipulate variables to establish cause-and-effect relationships, offering strong internal validity yet sometimes hindering external validity. Lastly, triangulation involves using various methods or data sources in one study, enhancing the validity and completeness of research findings.