Quantitative Research Design (Part 2)

Non-Experimental Designs

- observational research

- Most nursing studies are of this design because most human characteristics cannot be experimentally manipulated

- Most variable can not be manipulated ethically

Non-Experimental Designs

1. Descriptive-Normative or Survey

2. Correlational

3. Casual-Comparative or Ex Post Facto

Descriptive-Normative/Survey

A. Longitudinal Survey

B. Cross-sectional Survey

Longitudinal Survey

- Studies in which the same group of subjects are studied over time

- Trend studies, Cohort studies, Panel studies

Trend studies

use the same population across time but use different samples from that population each time

Cohort studies

examine a specific group (same population) over time

Panel studies

cohort studies that use the same samples each time

Cross-Sectional Survey

- Attempt to stimulate longitudinal data in a shorter time frame

- Data are gathered from multiple samples of the same population simultaneously

Cross-Sectional Survey

May be used to study a phenomenon at one time or to gather data from multiple groups at the same time

Types of Survey Administration

- Direct Administration

- Mailed Survey

- Telephone Interview

- Personal/face-to-face interview

Correlational

A. Retrospective correlational or case-control study

B. Prospective correlational or cohort study

C. Descriptive correlational

Correlation does not prove causation.

Retrospective Design

A phenomenon existing in the present is linked to phenomena that occurred in the past

Retrospective Design

The researcher begins with the dependent variable (the effect) and then examines whether it is correlated with one or previously occurring independent variables (potential causes)

Prospective Design

- Cohort Design

- Researchers start with a presumed cause and then go forward in time to the presumed effect

Ex-Post Facto Studies

- Used to investigate causal relationships

- Examine whether one or more pre-existing conditions could possibly have caused subsequent differences in groups of subjects

- some sources would categorize this as a quasi-experimental study

Ex-Post Facto Studies

Researchers attempt to discover whether differences between groups have resulted in an observed difference in the independent variable

Ex-Post Facto Studies

Examples:

- What is the effect of day care on the social skills of children?

- What is the relationship between participation in extracurricular activities and self concept?

Quantitative Designs

2 main classifications:

- Descriptive or analytical

- Experimental or non-experimental

Descriptive

- describes

- more exploratory

- profiles group characteristics

Descriptive

- "what"

- assumes NO hypothesis

- does not require comparisons between groups over time

Epidemiology

The study of how often diseases occur in different groups of people and why

Epidemiological information

used to plan and evaluate strategies to prevent illness and as a guide to managing patients in whom the disease has already developed

Epidemiology

Purposes:

- To understand what risk factors are associated with a specific disease, and how this disease can be prevented in groups of individuals

- "OBSERVE"

Epidemiology

Would want to predict and know more about the disorder by studying and discovering the risk factors, the protective factors in order to prevent further spread and mitigate the spread of the disorder properly.

Descriptive

Types:

- Case studies or case series

- Descriptive cross-sectional/prevalence surveys

- Ecologic descriptive studies

Hierarchy of study designs

1. Experiments/Intervention studies

2. Cohort studies

3. Case-control studies

Hierarchy of study designs

4. Prevalence studies/surveys

5. Ecologic studies

6. Case series

7. Case reports

Case studies/Case series

- A simple descriptive account of interesting characteristics observed in a group (series) of subjects

- Subjects do not necessarily have to be persons - they can be organizations, institutions, political units (province, municipality, barangay etc.)

Case studies/Case series

- Generally involve subjects seen over a relatively short period of time

- Does not include control subjects

- Does not involve any research hypothesis

Case studies/Case series

Findings generally lead to generation of hypothesis that are subsequently investigated in a cohort, case-control, or cross-sectional study

Descriptive cross-sectional/prevalence surveys

- Involves the collection of data on the occurrence and distribution of the disease of interest in population

- Also used in health systems research to describe prevalence according to patterns of health service utilization and compliance

- KAP surveys

Descriptive cross-sectional/prevalence surveys

To characterize the disease, the prevalence is usually computed for specific categories of variable related to:

- Person

- Place

- Time

Ecologic descriptive studies

- Unit of observation and unit of analysis is an aggregate rather than individual persons

- They are used to generate hypothesis, or as a quick method of examining associations

Ecologic descriptive studies

Most practical design to use when exposure level is relatively homogenous in a population but differs between populations (ex., water quality) or when individual measurements of exposure are impossible

ecological fallacy

- the most serious flaw of ecologic descriptive studies

- ie., the characteristics of the geographical unit are incorrectly attributed to individuals

Analytic

Types:

1. Cohort studies

2. Case-control studies

3. Cross-sectional studies

4. Experimental studies and clinical trials

#1-3 are observational studies

Observational studies

Core elements of investigation the relationship between disease and exposure

Prospective Cohort Study

- Start from the present

- Conduct a follow-up after study

Retrospective Cohort Study

- From the past

- Check for exposed and unexposed sample from past data

Advantages of Cohort Studies

1. May yield information on the incidence of the disease

2. Possible to compute for the relative risk

3. The temporal relationship between exposure and disease is clearly defined

Advantages of Cohort Studies

4. The design is particularly efficient for studies involving rare exposure factors

5. It is the strongest observational design for establishing cause-effect relationships

Disadvantages of Cohort Studies

1. Time consuming

2. Often requires a large sample size

3. Expensive

Disadvantages of Cohort Studies

4. Not efficient for the study of rare diseases

5. Losses to follow-up may diminish validity

6. Changes over time in diagnostic methods may lead to biased results

Advantages of Case Control Studies

1. Feasible when dealing with RARE disease

2. Requires a smaller sample size than a cohort study - easy for follow-up

3. Little problem with attrition

Disadvantages of Case Control Studies

1. Incidence rates and attributable risk cannot be computed due to small sample size

2. The temporal sequence between disease and exposure may be a problem

3. Big chance for bias in the selection of cases and controls

Disadvantages of Case Control Studies

4. Difficult to obtain information on exposure if the recall period is too long

5. Selective survival may bias the comparison

Population-based case control studies

Cases and controls are sampled from a defined population

Population-based case control studies

Advantages:

1. Source population is better defined

2. It is easier to make certain that cases and controls come from the same source population

3. The exposure histories of the control are more likely to reflect those of persons without the disease of interest

Hospital-based case control Studies

- Investigator selects cases from persons with the disease of interest who are admitted to a particular hospital

- Controls are selected from persons admitted with other conditions but with no evidence of the disease of interest

Hospital-based case control Studies

Advantages:

- Subjects are more accessible

- Subjects tend to be more cooperative

- Background characteristics of cases and controls may be balanced

- Easier to collect exposure information from medical records and biological experiments

Hospital-based case control Studies

Possible disadvantages:

- Variety of case chosen

- Depending on the specialization hospital you are in

- Patient tends to reject participation

- Lesser sample size