31 Questions
What is the appropriate multivariable technique to use when the dependent variable is continuous and the independent variables are categorical?
Analysis of variance
What is the term used to describe an ANOVA with more than one independent variable?
N-way ANOVA
What is the primary difference between one-way ANOVA and N-way ANOVA?
The number of independent variables
When would you use a one-way ANOVA?
When there is only one independent variable
What is the purpose of ANOVA in medical research?
To analyze the results of an experimental study
Why should multivariable techniques be used with caution in medical research?
Because there are many potential pitfalls in their use
What experience is recommended for using multivariable techniques in medical research?
Expert advice is necessary
What would be the dependent (outcome) variable in the antihypertensive drug study?
The difference score (posttreatment SBP - pretreatment SBP)
Why is it not sufficient to only look for a statistically significant decrease in SBP?
A decrease in mean SBP from 150 to 148 mm Hg would be too small to be clinically useful
What is the problem with using multiple Student's t-tests to compare the groups?
It raises the problem of multiple comparisons
What is the ratio of the between-groups variance to the within-groups variance called?
F-test
What are the two measures of variance in ANOVA called?
Between-groups mean square and within-groups mean square
What is the result of using ANOVA to compare two means instead of using a t-test?
The p-values are identical, and the value of F = t^2
What is the purpose of ANCOVA in a controlled clinical trial?
To adjust the dependent variable for the pretreatment concentrations of arterial blood lactate
What type of multivariable analysis is used when the dependent variable and all independent variables are continuous?
Multiple linear regression
What is the result of entering only the first variable in a stepwise linear regression?
Simple regression analysis
How does the explanatory strength of the variables change as each new variable is entered in a stepwise linear regression?
It changes
What is the purpose of the stepwise procedure in linear regression?
To select the independent variables to include in the model
What is the ratio of between-groups variance to within-groups variance called?
F-ratio
What is the purpose of specifying an alpha level in advance?
To determine the significance of the results
What is the term for the process of determining which differences between means are greater than would be expected by chance alone?
Multiple comparison testing
What is the term for the distribution of the F-statistic?
F-distribution
What is the advantage of using ANOVA over the t-test?
It can be used to compare the means of multiple groups
What is the primary goal of ANOVA?
To explain the total variation found in one analysis
What is the term for a one-way ANOVA that includes two or more independent variables?
N-way ANOVA
What is the purpose of partitioning the sum of squares in ANOVA?
To explain the total variation found in one analysis
What is the difference between ANOVA and ANCOVA?
ANOVA is used when all independent variables are categorical, while ANCOVA is used when some independent variables are categorical and some are continuous
What is the term for the variation not caused by the independent variable in ANOVA?
Residual variation
What is the term for a study design where there are equal numbers of observations in each of the study groups?
Balanced design
What is the purpose of using ANOVA in a study to determine whether supplementing gonadotropin-releasing hormone with parathyroid hormone would reduce the osteoporosis-causing effect of gonadotropin-releasing hormone?
To examine the effects of treatment and other independent variables on bone loss
What is the term for the independent variable in a study that is used to predict the variation in a continuous dependent variable?
Categorical variable
Study Notes
Multivariable Analysis Procedures
- The choice of statistical method for multivariable analysis depends on the type of dependent and independent variables (continuous, ordinal, dichotomous, or nominal).
- The final choice of method depends on the investigator's experience, personal preference, and comfort with the methods.
Analysis of Variance (ANOVA)
- ANOVA is used when the dependent variable is continuous and all independent variables are categorical.
- ANOVA can be used to analyze the results of an experimental study.
- One-way ANOVA is used when there is only one independent variable.
- N-way ANOVA is used when there are more than one independent variable.
One-Way ANOVA (F-Test)
- The F-test is used to compare more than two means simultaneously.
- The null hypothesis for the F-test is that the mean change in the dependent variable will be the same for all groups.
- The F-test has the same general form as other critical ratios: the ratio of a measure of the effect (the differences between means) divided by a measure of the variability of the estimates.
- The assumptions for the F-test are similar to those for the t-test: normal distribution of the dependent variable, independence of the samples, and equal variances.
- The F-test requires an alpha level to be specified in advance.
ANOVA Table
- The goal of ANOVA is to explain the total variation in the dependent variable by partitioning the sum of squares into component parts.
- The ANOVA table is used to display the results of the analysis.
N-Way ANOVA
- N-Way ANOVA is used when there are two or more independent variables.
- The total variation is divided into the individual and joint effects of the independent variables and error.
Analysis of Covariance (ANCOVA)
- ANCOVA is used when the dependent variable is continuous and some independent variables are categorical and some are continuous.
- ANCOVA is used to adjust for the effects of continuous independent variables on the dependent variable.
Multiple Linear Regression
- Multiple linear regression is used when the dependent variable and all independent variables are continuous.
- The formula for multiple linear regression is similar to the general linear model formula.
- Stepwise linear regression is a common method for analyzing data in multiple linear regression.
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