Functions and Classifications of Research Design
A study design is crucial for translating conceptual hypotheses into operational plans. It guides the collection of data to answer research questions objectively, accurately, and economically. Research design aids in decision-making for completing research effectively by identifying procedures, ensuring quality, and classifying study designs based on contacts with the population, reference periods, and nature of investigation.
Download Presentation
Please find below an Image/Link to download the presentation.
The content on the website is provided AS IS for your information and personal use only. It may not be sold, licensed, or shared on other websites without obtaining consent from the author.If you encounter any issues during the download, it is possible that the publisher has removed the file from their server.
You are allowed to download the files provided on this website for personal or commercial use, subject to the condition that they are used lawfully. All files are the property of their respective owners.
The content on the website is provided AS IS for your information and personal use only. It may not be sold, licensed, or shared on other websites without obtaining consent from the author.
E N D
Presentation Transcript
Rerearch Design Ass.Prof.Dr. Baydaa Hameed Abdullah
Definition A study design is a specific plan or protocol for conducting the study which allows the investigator to translate the conceptual hypothesis into operational one. Study design is the plan for collection of data to answer the research question.
What does research design do? Helps take decisions about how to complete the entire research: Validly Objectively Accurately Economically
Functions of Research Design 1. The identification and/ or development of procedures and logistical arrangements required to undertake a study 2. Ensuring that the procedures are adequate in quality to obtain valid, objective and accurate answers to the research questions.
Classifications of Study Designs Three types of classifications on the basis of: 1. The number of contacts with the study population 2. The reference period of the study 3. The nature of the investigation
Advantages of descriptive studies 1. They use already available data. 2. They are less expensive and less time- consuming. 3. They describe the pattern of disease occurrence. 4. They formulate research hypothesis.
Case reports Researcher(physician) who see unusal preentation of a common desease and he describes the findings of this case,case description may take any relevant description of the finding. An unusual case may add to our Knowledge for example MI in very young person without ECG findings is unusual presentation of MI.
Case series(clinical series) When a group of cases of the disease are reported, but in this study we can not: *Study the aetiology of the disease * Testing the hypothesis * Have a control group But in the study it can help in generating hypothesis Example: vaginal cancer is very rare in young females if 10 cases were reported and studied it may help us to generate a hypothesis when we interrogated with stilbestrol taking during pregnancy among their mothers(this canbe done by further studies) Discovery of AIDS was a case series Many clincal studies are case series
Advantages of case reports or case series Use available clinical data 1. 2. Detailed individual data. 3. Add to our knowledge. 4. Suggest need for investigation (hypothesis generation).
Disadvantages of case report or case series 1.May reflect experience of one person or one clinician. 2. No explicit(clear) comparison group.
Ecological Studies: based on studying of a group of people not individual as in previous studies. Correlation data represent average exposure level rather than individual level so we do not have each person information Ecological studies can generate a hypothesis and need further confirmation , it provides just initial clues to causation Example : as meat consumption in different countries increases prevalence of ca colon increases , Cigarette smoking increases ca lung prevalence increases as well
Advantages of Correlational Study 1. They describe the disease in the entire population in relation to the factor of interest. 2. They use the correlation coefficient (r) to measure the association between the two variables of interest. 3. They are easy to do, inexpensive and can be conducted quickly. 4. They represent the first step in searching for exposure-disease relationship (generate hypothesis) 5. They use available data (administrative or other aggregate data).
Disadvantages of correlational study Correlation data represent average exposure level rather than actual individual values. Data on exposure and data on outcome are collected independently. 2. No assurance that persons with exposure (risk factor) of interest are the same ones with outcome (disease) of interest. 3. Inability to link exposure with the disease in particular individual. What is missing: relationship between exposure and outcome at the individual level (incomplete design) 1. 4.
Cross-Sectional studies (prevalence studies or surveys) Cross-sectional: where only ONE set of observations is collected at a certain point in time, disregarding the length of time of the study as a whole It is a study of a group of people at a point in time for the prevalence of a disease or an attribute in a well defined population but data is collected at individual levels. In this study the measurements of exposure and effect are made at the same time . In cross- sectional studies, we are looking for both exposure and outcome
Study Design based on no. of contact with the population Cross Sectional Studies: One-shot or Status studies: One time contact Most commonly used design in social sciences Obtain overall picture Very simple design: Decide what you want to find out about, identify the study population, select a sample and contact your respondents to find out the required information
Advantages of cross sectional study Provide generalization from the sample to the population. They are short term expensive. Provide good information for the health problems and good for health planners to assess health care needs. Used for generating hypothesis to be test in further studies.5. diseases 1. studies and not 2. 3. 4. Adapted to chronic
Disadvantages 1.It is difficult to separate cause and effect 1- because measurement of exposure and disease are made at one point of time and it is impossible to determined which came first. 2- Cases detected (survivors) leading to survival bias cases cured or died are not detected. are prevalent cases
3.Possible measurement error; not suitable for rare conditions; 4.Non response and this will affect the representation of the sample. 5.Not adapted to incidence measurement 6.Not adapted to severe / acute diseases
A case control study Begins cases(diseases) which should represent all cases from a specified population. with the selection of The most difficult task is to select controls (people with no disease) the controls should represent people who would have been designated study cases if they had developed the diseases.
Case control study An important aspect of this study is the determination of the start and duration of exposure, the exposure status is usually determined after the development of the disease (retrospective) and usually by direct questioning of the affected person. Exposure may be determined by biochemical measurement, established recording system.
Case control study Exposure ? ? Disease Controls Retrospective nature
Sources of selection of cases in case control study Hospital-based case control study: the cases will be identified from the hospital or other health care facilities. These are common, relatively easy and inexpensive. Population-based case control study: It involves locating and obtaining data from all affected individuals or a random sample from population.
Selection of controls in case control study It is the most difficult aspect of Case Control Study (CCS), it depends on: Characteristics and sources of cases. Need to obtain comparable and reliable information from cases and controls. Practical and economic considerations. 1. 2. 3.
The control should be comparable to the source of the population of cases. Any exclusion or restrictions made in the selection of cases should be applied equally to the controls and vice versa.
Advantages: Suitable for rare diseases . Results can obtained quickly. Relatively inexpensive and short term study Small sample size Available data No ethical problem 1. 2. 3. 4. 5. 6.
Disadvantages of case control studies Incidence or absolute risk cannot be determined directly from a case control study. Temporal relationship exposure-disease difficult to establish Difficulty in selection the control. Case- control study rely upon retrospective data which lead to recall bias. Because the data are collected after Can not use to establish prevalence 1. 2. 3. 4. be whether 5. (retrospectively) it difficultto is correlation is causal or not.
Cohort Study: (follow up study, prospective , panel study, longitudinal, incidence) Follow up study or incidence study Begin with a group of people (a cohort) free of disease, who are classified into subgroups according to exposure to potential cause of disease, and the whole cohort is followed up to see how the subsequent development of new cases of the disease differ between the groups with and without exposure, cohort study is a longitudinal study cohort study provides the best information about the causation of disease and the direct measurement of the risk of developing disease.
Cohort study Identify group of Exposed subjects Un exposed subjects Measure incidence of disease Compare incidence between exposed and unexposed group
Direction of inquiry Time Diseased Exposed Non-diseased Cohort Population Diseased Not exposed Non-diseased Figure shows cohort study design
Experimental Design The researcher introduces the intervention that is assumed to be cause of change and waits until it has produced or has been given sufficient time to produce the change. The independent variable can be observed , introduced, controlled or manipulated by the researcher.
An experimental study can be carried out in either a controlled or a natural environment. Study population in a controlled situation: Study Population in a natural situation, population is in its natural environment such as a room.
Blind Studies In a blind study, the study population does not know whether it is getting real or fake treatment or which treatment modality. The main objective of blind study is to isolate the placebo effect: the psychological effect Usually applied to studies measuring the effectiveness of a drug or treatment.
Double- Blind Studies Concept similar to that of a blind study except that it also tries to eliminate researcher bias by concealing the identity of the experimental and placebo groups from the researcher. Neither the researcher nor the study participants know who is receiving real and who is receiving fake treatment or which treatment model they are receiving.
