Research Flashcards
Cohort Design
“Prospective studies” are where a group of identified subjects, exposed to a similar situation are observed over time.
Difference between an RCT and a Cohort study is that the allocation of subjects is not under the control of the investigator because the investigator must find another group of subjects similar to “exposed” in terms of other important factors.
Advantages of Cohort studies are that they are less expensive and less time-consuming than RCT’s.
Single Case Design
In this design one subject is followed over time, and evaluated on outcomes of interest. Subject serves as their own “control” and they are evaluated both before and after the intervention. This design is useful when a few clients have a particular diagnosis or are involved in a treatment that you want to evaluate.
Sometime it is difficult to conclude that the treatment alone resulted in any differences as other factors may change over time, for example the disease severity may change.
Before-after design:
This design is used to evaluate a group of subjects involved in a treatment where the evaluator collects information about the initial status of a group and compares it with an information about the outcomes after treatment is received.
This is a useful design when you do not wish to withhold treatment from any subjects, however with no “control” group, it is impossible to judge if the treatment alone was responsible for any changes in the outcomes.
Case control design
Retrospective study exploring what makes a group of individuals different by looking at an issue after it has happened.
Study compares the differences between subjects with a defining characteristic or situation with a similar (control) group of people who do not have the characteristic or are not involved in the situation of interest.
Design is inexpensive with problems related to difficulties to conclude what factors are responsible for the outcomes.
Cross Sectional Design
By using surveys, questionnaires and interviews this design is used to explore factors that may have influenced a particular outcome in a group of people. Evaluation of the group is carried out at the same time and it is useful when little is known about an issue.
Limitation is that it is impossible to know if all factors have been evaluated, so it is difficult to draw cause-effect conclusions from the results beyond the group of people being studied.
Case Study Design
A case study is carried out in order to provide descriptive information about the relationship between a particular treatment and an outcome of interest. There is no control group.
It is often used to explore a new treatment, when there is little knowledge but the results can only be considered in terms of describing a particular situation.
It may generate information to support further study of the topic of interest
Biases
A bias affects the results of a study either by favoring the treatment group or the control group.
The most common biases are:
1. Sample selection biases - subjects in the sample being unrepresentative of the population which you are interested in
2. Measurement biases - related to how the outcome of interest was measured
3. Intervention biases- involves how the treatment itself was carried out.
Sample selection biases
subjects in the sample being unrepresentative of the population which you are interested in
Measurement biases
related to how the outcome of interest was measured
Intervention biases
involves how the treatment itself was carried out.
Volunteer or referral bias
People who volunteer to participate in a study, or who are referred to a study by someone are often different than non-volunteers/non-referrals. This bias usually, but not always, favors the treatment group, as volunteers tend to be more motivated and concerned about their health.
Seasonal bias
If all subjects are recruited and thus are evaluated and receive treatment at one time, the
results may be influenced by the timing of the subject selection and intervention. For
example, seniors tend to be healthier in the summer than the winter, so the results may be
more positive if the study takes place only in the summer. This bias could work in either direction, depending on the time of year`
Attention bias
People who are evaluated as part of a study are usually aware of the purpose of the study, and as a result of the attention, give more favorable responses or perform better than people who are unaware of the study’s intent. This bias is why some studies use an “attention control” group, where the people in the control group receive the same amount of attention as those people in the treatment group, although it is not the same treatment.
Measurement Biases
Number of outcome measures used:
Bias can be introduced if only one outcome measure is used or if there are too many outcome measures for the sample size
Lack of “masked” or “independent” evaluation:
If the evaluators are aware of which group a subject was allocated to, or which treatment a person received, it is possible for the evaluator to influence the results by giving the person or group of people, a more or less favorable evaluation. It is usually the treatment group that is favored.
Recall or memory bias:
This can be a problem if outcomes are measured using self-report tools, surveys or interviews that are requiring the person to recall past events. Often a person recalls positive memories more than negative ones, and this can favor the results of the study for those people being questioned about an issue or receiving treatment.
