Biostatistics Lecture Notes PDF

BIOSTATISTICS DR. HEBA EL SHAWADFY GHALY Lecturer At The Faculty Of Physical Therapy Sinai University Summer 2024 Research Design  Research Design Descriptive studies: (one group) describe occurrence of outcome. Analytic studies: (comparison gro...

BIOSTATISTICS DR. HEBA EL SHAWADFY GHALY Lecturer At The Faculty Of Physical Therapy Sinai University Summer 2024 Research Design  Research Design Descriptive studies: (one group) describe occurrence of outcome. Analytic studies: (comparison groups) describe association between exposure and outcome  Descriptive Studies Describe the frequency, natural history and possible determinants of the disease. Show how many people develop a disease over time. Describe the characteristics of the disease and those affected. Generate hypotheses about the cause of the disease. Other studies could be developed based on the generated hypothesis. There are no comparison groups. They do not allow assessment of the association between risk factors and disease. Descriptive studies  Case reports and Case series Done for rare or unexpected conditions Reported for a small number of individuals Represent a warning alarm can help to identify new clinical issues and may lead to development of hypotheses. normally regarded as low level evidence as the observations may be subject to bias. Analytical studies  Observational designs Used to measure the association between 2 variables: Etiology (smoking and lung cancer) Pathology (proliferative retinopathy in diabetics)  Diagnosis (Diet and cancer colon)  Prevention (Sun light exposure & rickets in children)  Treatment (Use of anti prostaglandins in treating spasmodic dysmenorrhea ) Observational designs Observational designs Observational designs  Cross-sectional Studies Often used to study conditions that are relatively frequent with long duration of expression (nonfatal, chronic conditions) It measures prevalence, not incidence of disease Example: community surveys Not suitable for studying rare or highly fatal diseases or a disease with short duration of expression  Cross-sectional studies Disadvantages Weakest observational design, (it measures prevalence, not incidence of disease). The temporal sequence of exposure and effect may be difficult or impossible to determine Rare events a problem. Quickly emerging diseases, a problem Cross-sectional studies  Case-Control Studies An “observational” design comparing exposures in disease cases vs. healthy controls from same population exposure data collected retrospectively most feasible design where disease outcomes are rare  Case-Control Study Advantages  Less expensive and time consuming  Efficient for studying rare diseases Disadvantages  Inappropriate when disease outcome for a specific exposure is not known at start of study  Exposure measurements taken after disease occurrence  Disease status can influence selection of subjects Case-Control Study Case-Control Study  Cohort Studies An “observational” design comparing individuals with a known risk factor or exposure with others without the risk factor or exposure looking for the risk (incidence) of a disease over time Best observational design Data usually collected prospectively  Cohort Study Advantages  Exposure status determined before disease detection  Subjects selected before disease detection  Can study several outcomes for each exposure Disadvantages  Expensive and time-consuming  Inefficient for rare diseases or diseases with long latency  Loss to follow-up Cohort Study Cohort Study Cohort Study  Experimental Studies investigator can “control” the exposure generally, involves random assignment to groups clinical trials are the most well-known experimental design the ultimate step in testing causal hypotheses In an experiment, we are interested in the consequences of some treatment on some outcome. The subjects in the study who actually receive the treatment of interest are called the treatment group. The subjects in the study who receive no treatment or a different treatment are called the comparison group.  Randomized Controlled Trials (RCTs) A design with subjects randomly assigned to “treatment” and “comparison” groups Provides most convincing evidence of relationship between exposure and effect Not possible to use RCTs to test effects of exposures that are expected to be harmful, for ethical reasons  Control The comparison group is similar to the intervention group in everything except for the intervention It Ensures that outcome is really related to intervention What to give to the control: Standard Care Earlier or later application of same intervention Higher or lower dose level Placebo No treatment  Randomization Every subject have equal chance to be allocated to any group Importance:  To eliminate bias in treatment assignment (selection bias)  Ensure (but does not guarantee) balance regarding confounders Methods:  Coin  Dice  Random table  Envelops  Blinding Single blind trial The trial is so planned that the participant is not aware whether he/she belongs to the study group or control group. Double blind trial The trial is so planned that neither the doctor nor the participant is aware of the group allocation and the treatment received. Triple blind trial This goes one step further. The participant, the investigator, and the person analyzing the data are all not aware "blind“.  Randomized Controlled Trials Advantages the “gold standard” of research designs provides most convincing evidence of relationship between exposure and outcome Disadvantages Very expensive may be unethical  Non-randomized controlled trials Subjects of intervention & control groups are not chosen randomly the intervention are compared with those who do not volunteer.  Systematic Review and Meta analysis: Represents the top of evidence research pyramid Systematic Review: comprehensive survey of a topic in which all of the primary studies of the highest level of evidence have been systematically identified, appraised and then summarized  Meta-analysis survey in which all the studies are similar enough statistically that the results are combined and analyzed as one study Pyramid of Evidence