General Class Notes Flashcards
Case Report Vs. Case Series:
- Case report—detailed report of specific features of case
- Case series—systematic review of common features of a small number of cases
Advantages and Disadvantages of Case Series:
- Advantage: cost-efficient
- Disadvantages: no comparison group, no specific research question
Issues with Case Studies:
- Simplest design—description of interesting observations in a small number of individuals
- Usually case series do not involve control patients (i.e., patients free of disease)
- Usually leads to generation of hypotheses for more formal testing (sometimes just an overall investigation, not as in depth)
- Criticisms: not planned, no research hypotheses
Define what a Cross-Sectional Study is:
Cross sectional study is done at a fixed POINT in time. It is sort of a “moments glance” at a situation, does not take place over a period of time.
Advantages: cost-efficient, easy to implement, ethical
Disadvantages: no temporal information, non-response bias
Prospective Cohort Study
Observational study involving a group (cohort) of individuals who meet inclusion criteria followed prospectively in time for risk factor and outcome information
Advantages: can assess temporal relationships
Disadvantages: need large numbers for rare outcomes, confounding
Basic Idea: Is that you are selecting the group and then following them over a period of time.
Steps of a Cohort Study
- Identify a group of individuals that meet inclusion criteria.
- Follow prospectively in time.
- Assess exposure.
- Evaluate outcome status.
Bias is less of a problem in these sorts of studies. However, confounding may be a problem as there may be things that are impacting them all, but you aren’t going to get selection bias, or response bias as you generally have no idea who is going to have the disease etc.
Case-Control Study
Observational study involving individuals with (cases) and without (controls) outcome of interest.
Advantages: cost and time efficient for rare outcomes
best for diseases with long latency.
can investigate an array and variety of exposures
cost and time efficient
Disadvantages: need careful selection of cases and controls, bias. Bias can be a problem here
its cost and time efficient
In these studies investigation is retrospective in time. Basically looking at what caused the issue.
Compare groups with respect to proportions with a history of exposure (possible cause).
Issues with Case-Control Studies, what are the types of bias?
- Selection: Might have members drop out or lose interest
- Observation: knowledge of disease might lead to possible issues and overestimating results
- Recall Bias: Retrospective (for long term studies)
Randomized Control Trial
- You apply the exposure
- This is ideal for many studies because you hold so much control as the researcher
- This is quite expensive, it can be tricky to use as it requires extensive monitoring.
**Key in this study is to try to blind both the observers and the patient, the idea is that that way you will be less likely to get as many issues with observation bias etc. (basically placebo differentiation)
Steps of the Randomized Control Trial
- Randomization
- Control Group (Be aware of ethical issues)
- Monitoring (Interm analysis)
- Data and safety monitoring board
- Data management
- Reporting
Practice Problems:
- An investigator wants to assess whether smoking is a risk factor for pancreatic cancer. Electronic medical records at a local hospital will be used to identify 50 patients with pancreatic cancer. One hundred patients who are similar but free of pancreatic cancer will also be selected. Each participant’s medical record will be analyzed for smoking history. Identify the type of study proposed and indicate its specific strengths and weaknesses.
What is likely the biggest form/source of bias?
This is a case control study because they are looking back at the studies.
A weakness of a study like this could likely be the generalizability. Given they are all at one hospital there may be an issue will being able to apply it to other contexts. Exposure data is taken from records which may not actually show the exposure or accurate record of people who may actually smoke.
The most likely source of bias is misclassification bias, particularly with regard to classification of smoking status (exposure) because smoking information will be collected from the medical record.
Practice Problems:
- An investigator wants to assess whether the use of a specific medication given to infants born prematurely is associated with developmental delay. Fifty infants who were given the medication and 50 comparison infants who were also born prematurely but not given the medication will be selected for the analysis. Each infant will undergo extensive testing at age 2 for various aspects of development. Identify the type of study proposed and indicate its specific strengths and weaknesses.
Case Control study. This is because the cases are already known at the start of the study, and then exposure to this medication is controlled. The weaknesses are that this is a very costly study to do, confounding could also be a factor in this. Benefit of the study is that it is prospective in nature. Confounding may be a big issue when it comes to parents and investigating new borns because there are so many different factors.
- A study is planned to assess the effect of a new surgical intervention for gallbladder disease. One hundred patients with gallbladder disease will be randomly assigned to receive either the new surgical intervention or the standard surgical intervention. The efficacy of the new surgical intervention will be measured by the time a patient takes to return to normal activities, recorded in days. Identify the type of study proposed and indicate its specific strengths and weaknesses.
Randomized control trial. Strength of a randomized control trial is that it reduces the chance of confounding factors. Weaknesses are that it doesn’t bode well for generalizability.
Clinical trials are often weak because they are so specific and can not be applied very widely.
- An investigator wants to assess the association between caffeine consumption and impaired glucose tolerance, a precursor to diabetes. A study is planned to include 70 participants. Each participant will be surveyed with regard to their daily caffeine consumption. In addition, each participant will submit a blood sample that will be used to measure glucose level. Identify the type of study proposed and indicate its specific strengths and weaknesses. How would you make this a clinical trial?
My first thought is the confounding factors because there is always more things associated with people who drink coffee.
- this study is for a fixed period of time so it is cross sectional.
- to make this a clinical study, you would be assigning different people to consume caffeine and others to not.
- A study is planned to compare two weight-loss programs in patients who are obese. The first program is based on restricted caloric intake and the second is based on specific food combinations. The study will involve 20 participants and each participant will follow each program. The programs will be assigned in random order (i.e., some participants will first follow the restricted-calorie diet and then follow the food-combination diet, whereas others will first follow the food-combination diet and then follow the restricted-calorie diet). The number of pounds lost will be compared between diets. Identify the type of study proposed and indicate its specific strengths and weaknesses.
Cross-over trial. This is a type of longitudinal study.
