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Study designs


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Integrated Dentistry I
Third Year

Published in: Health & Medicine, Technology
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Study designs

  1. 1. DENTED 371 Study designs
  2. 2. Sources of evidence • Scientific evidence is the product of: – Well-designed – Well-controlled research investigation that minimize sources of bias. • Evidence is considered the synthesis of all valid research studies that answer a specific question.
  3. 3. Sources of evidence • Historically, what were the sources of evidence? • What are the types of evidence-based sources?
  4. 4. Sources of evidence • Quantitative research – Focuses on establishing cause and effect relationships through testing a specific hypothesis and reporting the results in statistical terms. – Experimental – Nonexperimental
  5. 5. Sources of evidence • Qualitative research (0123%4‫ا‬ !"#$%&‫ا‬ – Is exploratory and uses an interpretive, naturalistic approach that focuses on how individuals or groups view or understand their surroundings and construct meaning out of their experiences, ()"*+ ,-./ ‫!ﻟﺒﺤﺚ !ﻟﻨﻮﻋﻲ‬ 0J I!‫ 0ﻓ:ﻢ !ﻷﻓﺮ‬F‫ !ﺳﺘﻜﺸﺎﻓﻲ, 0ﻳﺴﺘﺨﺪ5 !ﻟﺘﻔﺴ7ﺮ9 0!ﻟﻨ:ﺞ !ﻟﻄﺒ7ﻌﻲ !ﻟﺬ? ﻳﺮﻛﺰ ﻋﻠﻰ ﻧﻈﺮ‬9‫ﺑ:ﻢ‬R‫ !ﻟﻤﻌﺎﻧﻲ ﻣﻦ ﺗﺠﺎ‬N!‫ ﻟﻤﺤ7ﻄ:ﻢ 0!ﺳﺘﺨﺮ‬M‫!ﻟﺠﻤﺎﻋﺎ‬
  6. 6. Nonexperimental studies • Purpose and study design – Observational studies systematically describe and interpret conditions/relationships that already exist. – Examines the association between exposure and a risk factor or between a disease and hypothesized risk factor. – A treatment or intervention is not given. ‫ﻋﻮ#ﻣﻞ #ﻟﺨﻄﺮ #ﻟﻤﻔﺘﺮﺿﺔ‬
  7. 7. Nonexperimental studies • Data collection – Gathers data without giving a treatment or intervening to control variables. – Clinical exams, surveys or questionnaires. – Can be collected once or multiple times over time.
  8. 8. Nonexperimental studies • Role of the researcher – Tends to remain separate from the subject matter.
  9. 9. Nonexperimental studies • Analysis – Analysis occurs after all the data are collected. – Involves analysis of numerical data that can be combined and manipulated using statistical methods. – Results reported using numerical relations and statistical terms.
  10. 10. • Three commonly used study designs are discussed in this lecture: • Cross-Sectional Study • Cohort Study • Case Control Study
  11. 11. Cross-sectional study • Cross-sectional study designs are used when studying one or more variables within a given population at one point in time. • Such studies are useful for establishing associations rather than causality and for determining prevalence, rather than incidence. '‫ﺗﺤﺪﻳﺪ #ﻻﻧﺘﺸﺎ‬ ‫ﺑﺪ; #ﻹﺻﺎﺑﺔ‬
  12. 12. Cross-sectional study Advantages: • Simple and inexpensive • Ethically safe • Quick data collection • Attrition is not an issue • Holds time constant
  13. 13. Cross-sectional study Disadvantages: • Does not permit distinction between cause and effect • Recall bias susceptibility • Confounders may be unequally distributed between groups • Differences may be due to age/time effects or cohort effects • Inter-subject variability exists, making it harder to detect a difference ‫#ﻟﻨﺘ@ﺠﺔ‬D ‫ﻻﺗﺴﻤﺢ ﺑﺎﻟﺘﻔﺮﻳﻖ ﺑ@ﻦ #ﻟﺴﺒﺐ‬ P‫ﻣﻮ ﻛﻞ #ﻻﺷﺨﺎ‬ ‫ ﻟﻨﻔﺲ #ﻟﻤﺆﺛﺮ‬Q‫ﻳﺘﻌﺮﺿﻮ‬ ‫ﺑﺎﻟﻀﺒﻂ‬
  14. 14. Cohort study • In cohort studies, a group of people within a population is followed over a specified period of time to track who experiences or develops the same significant life event or treatment.
  15. 15. Cohort study • This type of design can be used "to study incidence, causes, and prognosis. Because they measure events in chronological order they can be used to distinguish between cause and effect."
  16. 16. Cohort study ‫ﻣﺴﺘﻘﺒﻠﻲ‬ • Cohort studies can be done prospectively, retrospectively, or using cross-sectional methods. As well, two groups may be followed: one containing the agent of interest and the other acting as a control group. ‫ﺑﺈﺛﺮ 'ﺟﻌﻲ‬
  17. 17. Cohort study Advantages: • Ethically safe • Subjects can be matched • Can establish timing and directionality of events • Eligibility criteria and outcome assessments can be standardized • Administratively easier and cheaper than Randomized Controlled Trial • Possible to examine multiple outcome variables ‫ﺿﻊ ﺗﻮﻗ@ﺖ‬D ‫ﻳﻤﻜﻦ‬ ^#‫ﺗﻮﺟﻪ #ﻷﺣﺪ‬D ‫ﻠ@ﺔ‬W‫#ﻟﻤﻌﺎﻳ@ﺮ #ﻷ‬
  18. 18. Cohort study Disadvantages: • The time to develop the disease may be long. • The cost of follow up • The potential for losing subjects over time. • For rare disease, large sample sizes or long follow-up necessary.
  19. 19. Case-Control study • Most commonly carried out retrospectively, case control studies are used to compare cases who have a certain condition with a control group known not to have developed the outcome of interest.
  20. 20. Case-Control study • The control group is usually not only taken from the same population base, but also matched for age and gender. Such studies "seek to identify possible predictors of outcome and are useful for studying rare disease or outcomes. They are often used to generate hypotheses that can then be studied via prospective cohort or other studies" _‫#ﻟﻔﺮﺿ@ﺎ‬
  21. 21. Case-Control study Advantages: • Quick and cheap • Only feasible method for studying very rare disorders or those with long lag between exposure and outcome • Fewer subjects needed than crosssectional studies.
  22. 22. Case-Control study Disadvantages: • Reliance on recall or records to determine exposure status • Confounders • Selection of control groups is difficult • Potential bias: recall, selection • Cannot calculate the relative risk *‫ﻋﻮ#ﻣﻞ #ﻹ'ﺑﺎ‬