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Lecture note on Over view of Research study.ppt
- 1. Overview of Overview of StudyDesigns Study Designs Engr Dr. Ocheri C. Engr Dr. Ocheri C. Biomedical Engineering Biomedical Engineering University of Nigeria, University of Nigeria, Nsukka Nsukka 12/31/25 1 cyril.ocheri@unn.edu.ng
- 2. Study Designs Study Designs Experimental Randomized Controlled Trial Group Randomized Trial Observational DescriptiveAnalytical Cross-sectional Ecological Cohort Case-control 12/31/25 2 cyril.ocheri@unn.edu.ng
- 3. Experimental v. Observational Experimentalv. Observational “ “Gold Standard” Gold Standard” Investigator controls Investigator controls exposure exposure Less common Less common Investigator observes Investigator observes exposures exposures Most common Most common 12/31/25 3 cyril.ocheri@unn.edu.ng
- 4. 4 INTERVENTION GROUP OUTCOME ASSESSMENT Present Future TIME Experimental Study: ExperimentalStudy: Randomized Controlled Trial Randomized Controlled Trial Randomly Assigns Intervention Comparison 12/31/25 cyril.ocheri@unn.edu.ng
- 5. Randomized Controlled Trial RandomizedControlled Trial Randomization is random distribution or Randomization is random distribution or allocation of subjects into groups allocation of subjects into groups Treatment or intervention group Treatment or intervention group Comparison group (placebo, another tx, no tx, usual Comparison group (placebo, another tx, no tx, usual care) care) Helps ensure that both groups are similar re: Helps ensure that both groups are similar re: known and unknown factors known and unknown factors Two types of RCTs Two types of RCTs Preventive trials Preventive trials Therapeutic trials Therapeutic trials 12/31/25 5 cyril.ocheri@unn.edu.ng
- 6. Group Randomized Trial GroupRandomized Trial Unit of assignment = group Unit of assignment = group Unit of analysis = individual (usually) Unit of analysis = individual (usually) Investigator controls exposure status Investigator controls exposure status Randomly assigns group to intervention group Randomly assigns group to intervention group Exposure assessed Exposure assessed before before outcome outcome 12/31/25 6 cyril.ocheri@unn.edu.ng
- 7. 7 Experimental Study Experimental Study Strengths Strengths Able to demonstrate Able to demonstrate causal association causal association Randomization deals with Randomization deals with known and unknown known and unknown confounders confounders Investigators directly Investigators directly control intervention control intervention Limitations Limitations Ethical concerns Ethical concerns (equipoise) (equipoise) Gen practice ≠ artificial Gen practice ≠ artificial Expensive Expensive Power often an issue Power often an issue 12/31/25 cyril.ocheri@unn.edu.ng
- 8. Observational Studies Observational Studies Most common, by necessity Most common, by necessity Observes nature without intervention Observes nature without intervention Takes advantage of people’s natural exposures Takes advantage of people’s natural exposures (choice, occupation, environment, residence) (choice, occupation, environment, residence) Collect data and statistically analyze results Collect data and statistically analyze results Goal is to “mimic” experimental study Goal is to “mimic” experimental study Statistics more important and usually more complex Statistics more important and usually more complex Can be descriptive or analytic Can be descriptive or analytic 12/31/25 8 cyril.ocheri@unn.edu.ng
- 9. Study Designs Study Designs Experimental Randomized Controlled Trial Group Randomized Trial Observational DescriptiveAnalytical Cross-sectional Ecological Cohort Case-control 12/31/25 9 cyril.ocheri@unn.edu.ng
- 10. Cohort Studies Cohort Studies Two ways to assemble cohort: Two ways to assemble cohort: Group of individuals with common characteristic or Group of individuals with common characteristic or experience (then assess exposure experience (then assess exposure before before outcome) outcome) Select subjects without outcome according to Select subjects without outcome according to exposure status (esp important for rare exposure) exposure status (esp important for rare exposure) Followed over time to determine incidence of Followed over time to determine incidence of symptoms, disease, or death symptoms, disease, or death Analysis focuses on risk of outcome in exposed Analysis focuses on risk of outcome in exposed compared to unexposed groups compared to unexposed groups Unexposed is referent or comparison group Unexposed is referent or comparison group 12/31/25 10 cyril.ocheri@unn.edu.ng
- 11. Prospective Cohort Studies ProspectiveCohort Studies Only include outcome-free individuals Only include outcome-free individuals At risk of developing outcome At risk of developing outcome Followed into future to observe outcomes Followed into future to observe outcomes Can take long time to complete Can take long time to complete Important to re-assess exposures over time Important to re-assess exposures over time Useful design for rare exposures Useful design for rare exposures Not for rare outcomes Not for rare outcomes Advantage: exposure assessed before subject Advantage: exposure assessed before subject knows outcome status; temporal sequence knows outcome status; temporal sequence 12/31/25 11 cyril.ocheri@unn.edu.ng
- 12. 12 EXPOSURE ASSESSMENT OUTCOME ASSESSMENT Present Future TIME Prospective CohortStudy Prospective Cohort Study Exposed Unexposed 12/31/25 cyril.ocheri@unn.edu.ng
- 13. Retrospective Cohort Studies RetrospectiveCohort Studies Both exposure and outcome occur before study Both exposure and outcome occur before study Studies only prior outcomes Studies only prior outcomes Historical cohort reconstructed from existing Historical cohort reconstructed from existing data sources before study begins data sources before study begins Example: Effects of pesticide exposure on Example: Effects of pesticide exposure on cancer mortality (cohort of factory workers cancer mortality (cohort of factory workers employed by manufacturer identified from employed by manufacturer identified from personnel records) personnel records) Need good records with info on many variables Need good records with info on many variables Sometimes good outcome info not available Sometimes good outcome info not available 12/31/25 13 cyril.ocheri@unn.edu.ng
- 14. 14 EXPOSURE ASSESSMENT OUTCOME ASSESSMENT Past Present TIME Retrospective CohortStudy Retrospective Cohort Study Exposed Unexposed 12/31/25 cyril.ocheri@unn.edu.ng
- 15. 15 Cohort Study Cohort Study Strengths Strengths Easier to differentiate Easier to differentiate cause from effect cause from effect Direct estimation of Direct estimation of incidence incidence Able to examine multiple Able to examine multiple outcomes outcomes Efficient for rare Efficient for rare exposures exposures Prospective Prospective Reduces recall bias Reduces recall bias Limitations Limitations Large sample size Large sample size Prospective Prospective Long-term follow-up Long-term follow-up Expensive Expensive 12/31/25 cyril.ocheri@unn.edu.ng
- 16. Case-Control Studies Case-Control Studies Both exposure and outcome have occurred Both exposure and outcome have occurred Classified according to outcome status Classified according to outcome status before before exposure ascertained exposure ascertained Cases with outcome selected from well-defined Cases with outcome selected from well-defined source population source population Controls without outcome* sampled from Controls without outcome* sampled from population that produced cases population that produced cases Analysis focuses on odds of Analysis focuses on odds of exposure exposure in cases in cases compared to controls compared to controls 12/31/25 16 cyril.ocheri@unn.edu.ng
- 17. Case-Control Study Case-Control Study Grouped on basis of past or current outcome Grouped on basis of past or current outcome Outcome already occurred before exposure Outcome already occurred before exposure assessed assessed May lead to biased recall May lead to biased recall May be difficult to establish temporality May be difficult to establish temporality Useful design for rare outcomes Useful design for rare outcomes Not for rare exposures Not for rare exposures Advantages: Advantages: Less expensive than cohort (usually) Less expensive than cohort (usually) Can look at multiple exposures Can look at multiple exposures 12/31/25 17 cyril.ocheri@unn.edu.ng
- 18. 18 EXPOSURE ASSESSMENT OUTCOME ASSESSMENT Past Present TIME Case-Control Study Case-ControlStudy Cases (with outcome) Controls (without outcome)* 12/31/25 cyril.ocheri@unn.edu.ng
- 19. 19 Case-Control Study Case-Control Study Strengths Strengths Efficient for rare Efficient for rare outcomes outcomes Able to examine multiple Able to examine multiple exposures exposures Limitations Limitations ↑ ↑ possibility of bias possibility of bias Temporal association Temporal association Inefficient for rare Inefficient for rare exposures exposures 12/31/25 cyril.ocheri@unn.edu.ng
- 20. Cross-Sectional Studies Cross-Sectional Studies Study population not selected based on outcome Study population not selected based on outcome or exposure status or exposure status Outcome and exposure assessed at same time Outcome and exposure assessed at same time Snapshot at single point in time Snapshot at single point in time Problems inferring temporal sequence Problems inferring temporal sequence Identify prevalent cases of long duration Identify prevalent cases of long duration 12/31/25 20 cyril.ocheri@unn.edu.ng
- 21. 21 EXPOSURE ASSESSMENT OUTCOME ASSESSMENT Past Present TIME Analytical Cross-SectionalStudy Analytical Cross-Sectional Study Exposed Unexposed 12/31/25 cyril.ocheri@unn.edu.ng
- 22. 22 Cross-Sectional Study Cross-Sectional Study Strengths Strengths Less time and resources Less time and resources No follow-up time No follow-up time involved involved More representative of More representative of well-defined general well-defined general population population Useful when onset is Useful when onset is difficult to establish difficult to establish (incidence) (incidence) Limitations Limitations Temporal association Temporal association Potential for prevalence- Potential for prevalence- incidence bias incidence bias Not for rare exposures or Not for rare exposures or outcomes outcomes Reverse causality Reverse causality 12/31/25 cyril.ocheri@unn.edu.ng
- 23. 23 EXPOSURE ASSESSMENT OUTCOME ASSESSMENT Past Present TIME Analytical EcologicalStudy Analytical Ecological Study Exposed Unexposed Note: Often in ecological studies, the exposures and outcomes are continuous measures 12/31/25 cyril.ocheri@unn.edu.ng
- 24. 24 Ecological Study Ecological Study Strengths Strengths Relatively quick and Relatively quick and inexpensive inexpensive May be only appropriate May be only appropriate design for research question design for research question May be useful when intra- May be useful when intra- group variability in group variability in exposure is small exposure is small May provide greater inter- May provide greater inter- group variability across group variability across larger ecological units larger ecological units Limitations Limitations Ecological fallacy Ecological fallacy Secondary data sources Secondary data sources Confounding Confounding Temporal association Temporal association Migration across groups Migration across groups 12/31/25 cyril.ocheri@unn.edu.ng
- 25. Characteristics of StudyDesigns Characteristics of Study Designs Unit of observation E assessed before outcome? Investigator controls E? RCT Individual Yes Yes Group RCT Group Yes Yes Cohort Individual Yes No Case- control Individual No No X-sectional Individual No No Ecological “Group” No No •Exposure(s) of interest? •Outcome(s) of interest? •Population investigated? •Recruitment? •Study design? •Strengths? •Limitations? 12/31/25 25 cyril.ocheri@unn.edu.ng