Biostats finals

• Observational designs for generating hypothesis

  • Qualitative studies
  • cross sectional surveys
  • cross sectional ecologic studies
  • longitudinal ecologic studies
• Function of research design

  • to answer the question using appropriate collected data
• Hypothesis generating

  process of developing a list of possible candidates for the causes of the disease and obtaining initial evidence that supports one or more of these candidate.
• Hypothesis testing

  • testing the generated hypothesis then make predictions
  • examining new data ti determine if the predictions are correct
• Basic function of most epi research designs is either

  • descirbe the pattern of health problems accurately or
  • to enable a fair, unbiased comparison to be made between a group with and a group without a risk factor
• Qualitative research

  advantages:

  • generates hypothesis and initial explorations of issues in participant’s own language without bias of investigator

  Disadvantage:

  • cannot test hypotheses
  • can explore only what is stated/presented
  • has potential for bias
• ecologic studies

  advantage:

  • fairly quick and easy to perform
  • useful for hypothesis generation

  disadvantage:

  • do not allow for causal conclusions to be drawn because the data are not associated with individual persons
  • Not good for hypothesis testing
• Cross sectional surveys

  advantage:

  • quick and easy to use
  • useful for hypothesis generation

  disadvantage:

  • do not offer evidence of a temporal relationship between the risk factors and disease
  • subject to late-look bias
  • not good for hypothesis testing
• Cohort studies

  advantage:

  • can be retrospectively or prospectively
  • used to obtain a true absolute measure of risk
  • can study many disease outcomes
  • good for studying rare risk factors

  disadvantage:

  • time consuming and costly
  • can study knly the risk factors measured at the beginning
  • used only for common diseases
  • may have losses to follow up
• Case control studies

  advantage:

  • quick and easy to perform
  • can study many risk factors
  • good for studying rare diseases

  disadvantage:

  • obtain only relative measure of risk
  • subject to recall bias
  • selection of controls may be difficult
  • temporal relationships may be unclear
  • only one disease outcome at a time
• Randomized controlled trials

  advantage:

  • gold stamdard for evaluating treatment or preventive interventions
  • allow investigators to have extensive control over

  disadvantage:

  • time consuming and costly
  • can study only interventions or exposures that are comtrolled by investigators
  • may have problems related to therapy changes and dropouts
  • limited in generalizability
  • often unethical to perform
• Systematic reviews and metaanalysis

  advantage:

  • Allow exploration of subgroups
  • decrease subjective element of literature review increases statistical power
  • provide quantitative estimates

  disadvantage:

  • mixing poor quality studies together in a review or meta analysis does not improve the underlying quality of studies
• Types of research

  • observational
  • experimental
• Experimental

  • more control over the assignment of participants, often placing them in a treatment and control groups
• Observational studies

  • either descriptive or analytical
  • observes groups of study participants to leadn about the possible effects of a treatment or risk factor
  • assignment of participants to a treatment group or a control group remains outside the investigators control
• Descriptive

  • distribution of health related states
  • describe disease occurrence as to person, place, and time.
  • studies generate hypothesis
  • no hypothesis are specified in advance
  • preexisting data are often used
  • associations may or may not be causal
• Analytic

  • determinant of health related states
  • studies test hypotheses
  • hypothesis are specified in advance
  • new data are often collected
  • differences between groups are measured