Chapter 8: Descriptive and Predictive Research Designs: Understanding Conditions and Making Clinical Predictions

Descriptive Studies

explain health conditions and provide information about the incidence and prevalence of certain conditions within a diagnostic group

Predictive Studies

provide information about factors that are related to a particular outcome

Epidemiology

the study of health conditions in populations

Incidence

The frequency of new occurrences of a condition during a specific time period.

- Calculated as the number of new cases during a time period, divided by the total population at risk

Prevalence

The number of individuals in a population who have a specific condition at a given point in time, regardless of onset

- Calculated as the number of cases at a given time point, divided by the total population at risk

Incidence and Prevalence Studies

Help practitioners know how widespread a particular condition is and how likely someone is to develop it

Not possible to make conclusions regarding causation

Large samples needed in epidemiological studies result in the use of efficient data collection methods such as surveys

Ex Post Facto Comparisons

cross-sectional designs that compare two or more groups, often those with and without a certain condition, at one point in time

Developmental Research

longitudinal design used to compare groups

Group Comparison Studies

Lack of random assignment and manipulation of the independent variable present potential threats to validity.

Survey Research

Questionnaire is administered via mail, electronic media, telephone, or face-to-face contact

Advantages = ease with which large amounts of data can be collected, particularly when surveys are administered electronically; opportunity to use random sampling methods, as it is possible to reach individuals in different geographic locations

Response Rate

percentage of individuals who return a survey based on the total numbers of surveys administered

Response Bias

measurement error that creates inaccuracy in the survey results

Self-Reporting Issues

desire to present self in a favorable light

Cross-Sectional

Most surveys used in research are _____________ in nature (i.e., gather data at a single point in time).

Longitudinal

However, some surveys are _____________ and collect data over periods of years or decades.

Study Designs to Predict an Outcome

Two major categories:

1)Studies that use correlational methods

2)Studies using group comparison methods

Purpose = identify factors that are most predictive of an outcome

Correlational Studies

Examine the relationships between variables

In a simple correlation, the association between two variables is determined.

____________ ____________ are cross-sectional, with data collected at a single point in time.

May administer multiple measures and explore the relationships using a correlation matrix.

Complex Correlational Designs

Look at multiple predictors for a single outcome

Regression analysis used.

- To trust results, need large sample

These studies have the advantage of examining the total amount of variance accounted for by multiple predictors and the relative importance of each individual variable as a predictor.

Shared Variance

Multicollinearity

Circumstance in which variables are correlated with one another

To determine the unique variance of a predictor, it is entered last into the regression equation.

Two primary types of regression analyses that examine multiple predictors:

1)Multiple linear regression

2)Multiple logistic regression

Multiple Predictors

Multiple Linear Regression

Used when the outcome is a continuous variable

Multiple Logistic Regression

Used when the outcome and predictors are categorical variable

- Odds Ratio

Odds Ratio

Probability statistic that determines the likelihood that, if one condition occurs, a specific outcome will also occur

An ___________ ___________ of 1.0 means there is no difference between the groups. When the _____________ _____________ is greater than 1.0, there is a greater chance of experiencing the outcome; when the _____________ ______________ is less than 1.0, there is a lower chance of experiencing the outcome.

Case-Control Design

Observational, retrospective, cross-sectional study that can be used to answer prognostic research questions concerning which risk factors predict a condition

Landmark Example

Compared individuals with lung cancer with individuals without lung cancer and identified smoking as a predictor

Cohort Study

Observational, but differs from a case-control design in that participants are followed over time, making this design longitudinal

Hypothesized risk factor is identified and individuals with and without risk factor are followed to determine the impact that the risk factor has on the outcome.

Prospective Cohort Study

Research question identified before the study begins, and individuals are followed over time to determine who did and who did not develop the condition

Retrospective Cohort Study

Existing records or the client's report on past behavior is used to determine if changes occurred over time

Evaluating Descriptive and Predictive Studies

Cannot be analyzed using the levels-of-evidence hierarchy

When evaluating should consider:

- Control over outside variables

- Matching

- Use of statistical procedures to control for factors that might influence outcome

- Prospective studies are stronger than retrospective analyses

- Sample size

- Sampling bias

- Measurement methods

Level I

Systematic reviews of prospective cohort studies

Level II

Individual prospective cohort study

Level III

Retrospective cohort study

Level IV

Case-control design

Level V

Expert opinion, case study