Research Design and Statistics Lecture Notes
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Questions and Answers

What is the formula for calculating the mean sum of squares for the main effect of alcohol (MSB)?

  • MSB = SSB / dfB (correct)
  • MSB = SSA / dfA
  • MSB = SSAxB / dfAxB
  • MSB = SSR / dfR

Which statistical test is appropriate for examining the association between two categorical variables?

  • Regression
  • Pearson correlation
  • Chi-squared test (correct)
  • Spearman correlation

What type of analysis is used to predict a categorical outcome from one or more predictor variables?

  • Linear Regression
  • Analysis of Covariance (ANCOVA)
  • Factorial ANOVA
  • Logistic Regression (correct)

Which test is used to compare the means of more than two independent groups?

<p>One-way ANOVA (C)</p> Signup and view all the answers

What is the purpose of calculating effect size?

<p>To assess the magnitude of the main effects and interactions (C)</p> Signup and view all the answers

Which statistical test is most appropriate for assessing the relationship between two ordinal variables?

<p>Spearman Correlation (A)</p> Signup and view all the answers

A researcher wants to examine the effect of one continuous and one categorical variable on a continuous outcome. Which test would be most appropriate?

<p>ANCOVA (B)</p> Signup and view all the answers

What is the formula for calculating the F value for the interaction effect between Alcohol and FaceType?

<p>FAxB = MSAxB / MSR (A)</p> Signup and view all the answers

A researcher is comparing three groups non-parametrically. Which test should they use?

<p>Kruskal-Wallis (B)</p> Signup and view all the answers

Which of these is a non-parametric test used for repeated measures?

<p>Friedman (B)</p> Signup and view all the answers

How many levels can a categorical predictor have for analysis?

<p>Two or more (A)</p> Signup and view all the answers

What is the relationship between participant types and predictor levels in independent ANOVA?

<p>Participants must be independent for each level (D)</p> Signup and view all the answers

What is the implication of having the same participants for different predictor levels?

<p>It results in a dependent measure approach (C)</p> Signup and view all the answers

Which of the following is necessary for conducting multiple regression analysis?

<p>Both continuous and categorical predictors can be used (C)</p> Signup and view all the answers

In the model introduced, which of the following variables acts as a dummy variable for the treatment groups?

<p>Short (A), Long (C)</p> Signup and view all the answers

What is the purpose of including the continuous variable Puppylove in the model?

<p>To control for its effect on the dependent variable (B)</p> Signup and view all the answers

What does the notation $Y_i = b_0 + b_1 X_{1i} + b_2 X_{2i} + e_i$ represent in the model?

<p>A multiple regression model with categorical and continuous variables (B)</p> Signup and view all the answers

What is the purpose of having a covariate in an ANCOVA analysis?

<p>To account for variability in the outcome measure (C)</p> Signup and view all the answers

Which assumption of ANCOVA involves ensuring that the treatment effect and covariate are independent?

<p>Independence of the covariate (D)</p> Signup and view all the answers

What does the homogeneity of regression slopes assumption imply in an ANCOVA?

<p>The relationship between the covariate and outcome is consistent across groups (B)</p> Signup and view all the answers

In ANCOVA, what statistical tests are primarily focused on the covariate and predictor effects?

<p>Test of Between-Subjects effects (B)</p> Signup and view all the answers

What is one crucial characteristic of the effect of the covariate in ANCOVA analysis?

<p>It should be equal across all categorical groups (B)</p> Signup and view all the answers

What do the F and p values in the ANCOVA output indicate?

<p>The likelihood of rejecting the null hypothesis (D)</p> Signup and view all the answers

Why might adjusted means differ markedly from original group means in ANCOVA?

<p>They have been corrected for the covariate's effect (A)</p> Signup and view all the answers

Which statistical software feature is typically used to perform ANCOVA analysis?

<p>General Linear Model (A)</p> Signup and view all the answers

What does the interaction coefficient, b3, measure in the context of the study?

<p>How face type ratings depend on the dose of alcohol (B)</p> Signup and view all the answers

In the study, what is significant about the interaction being zero for conditions other than when both predictors are present?

<p>It suggests that the combination of face type and alcohol may enhance ratings differently. (A)</p> Signup and view all the answers

What would happen to the mean rating of attractive faces when alcohol and face type interact?

<p>It would be higher than ratings for unattractive faces with the same alcohol dose. (A)</p> Signup and view all the answers

How is the interaction represented in the model described in the study?

<p>As the product of dummy variables for face type and alcohol (C)</p> Signup and view all the answers

What is the mean rating for unattractive faces under high-dose alcohol?

<p>6.625 (C)</p> Signup and view all the answers

Which condition results in the lowest mean rating for face attractiveness?

<p>Unattractive faces under placebo (B)</p> Signup and view all the answers

What does the term 'dummy variables' refer to in this study?

<p>Representation variables for categorical data (A)</p> Signup and view all the answers

How is b1 calculated in relation to the unattractive face ratings?

<p>By subtracting the rating of attractive faces from unattractive faces under the same condition (C)</p> Signup and view all the answers

At what dosage does alcohol seem to have the least effect on the rating of attractive faces?

<p>Placebo (D)</p> Signup and view all the answers

What is the primary purpose of testing interactions in this study?

<p>To determine if alcohol's effect differs based on the attractiveness of faces (D)</p> Signup and view all the answers

What is the numeric difference between the mean rating of unattractive faces under high dose and unattractive faces under placebo?

<p>$4.125$ (D)</p> Signup and view all the answers

Given the ratings, what can be inferred about the influence of alcohol on unattractive faces under high dose?

<p>Alcohol significantly increases the ratings of unattractive faces. (A)</p> Signup and view all the answers

In the factorial design, which scenario presents the highest interaction effect?

<p>Unattractive, High Dose (A)</p> Signup and view all the answers

What is the significance of the mean values presented in the factorial design?

<p>They demonstrate how different factors influence mean ratings. (B)</p> Signup and view all the answers

Flashcards

ANOVA (Analysis of Variance)

A statistical test used to compare means of two or more groups when the independent variable has at least two levels and the dependent variable is continuous.

T-test

A statistical test used to compare means of two groups when the independent variable has two levels and the dependent variable is continuous.

ANCOVA (Analysis of Covariance)

A statistical test used to compare means of two or more groups when the independent variable has at least two levels, the dependent variable is continuous, and one or more additional variables (covariates) are included in the analysis.

Chi-squared test

A statistical test used to analyze the relationship between two or more categorical variables.

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Mann-Whitney U test

A statistical test used to compare means of two groups when the independent variable has two levels and the dependent variable is ordinal or ranked.

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Kruskal-Wallis test

A statistical test used to compare means of two or more groups when the independent variable has at least two levels and the dependent variable is ordinal or ranked.

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Friedman test

A statistical test used to compare means of two or more groups when the independent variable has at least two levels, the dependent variable is ordinal or ranked, and the data is repeated measures.

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Wilcoxon signed-rank test

A statistical test used to compare the means of two matched groups when the dependent variable is ordinal or ranked.

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Dummy variables

A type of variable used in regression analysis to represent categorical data, often with '0' representing absence and '1' representing presence of a specific category.

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Multiple regression model

A statistical model that uses multiple independent variables (predictors) to explain the variation in a dependent variable.

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Regression model with dummy variables and continuous covariates

A regression model where the dependent variable is continuous and the independent variables include both categorical variables (represented by dummy variables) and continuous variables.

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Discounting the effect of a continuous covariate

A method designed to remove the impact of a continuous variable on a dependent variable before analyzing the effect of categorical variables.

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Hierarchical regression

A statistical method for evaluating the influence of predictors on a dependent variable while considering the variance explained by other predictors already in the model.

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Homogeneity of regression slopes

ANCOVA assumes that the relationship between the covariate and the outcome variable is the same across all levels of the categorical predictor.

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Independence of the covariate and treatment effect

ANCOVA assumes that the covariate is not influenced by the categorical predictor. It means the relationship between the covariate and the outcome should not vary with the treatment group.

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Homogeneity of variance

ANCOVA assumes that the variance of the outcome variable is equal across all levels of the categorical predictor.

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Normality

ANCOVA assumes that the outcome variable follows a normal distribution within each group.

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Adjusted means

The adjusted means in ANCOVA reflect the average outcome for each group after accounting for the variability explained by the covariate.

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ANCOVA output: Test of Between-Subjects effects

ANCOVA uses F-test and p-value to determine the significance of the effect of the independent variable (categorical predictor) and the covariate on the dependent variable (outcome).

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Categorical predictor

The categorical predictor in ANCOVA, which groups different treatment conditions or levels. It's usually the independent variable for comparison.

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Continuous covariate

The continuous variable in ANCOVA that potentially affects the DV, but is not the primary focus of the analysis. It's usually a characteristic of participants.

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Interaction Effect

A statistical concept that investigates how the effect of one independent variable on the dependent variable varies depending on the levels of another independent variable.

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Independent Factorial Design

A type of experimental design that allows researchers to examine the unique effect of each independent variable and their combined interaction.

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Calculating Interaction Effect

The interaction effect is calculated by subtracting the effect of one independent variable on the dependent variable in the absence of the other variable from its effect in the presence of the other variable.

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Interaction Coefficient

The interaction coefficient, denoted as 'b3' in this case, reflects the strength and direction of the interaction effect. A positive interaction indicates that the effect of one variable is enhanced in the presence of the other, while a negative interaction suggests a reduced effect.

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Interaction as a Product

The interaction effect in this scenario is represented by the product of the dummy variables for 'FaceType' and 'Alcohol'. This means the interaction is only present when both 'FaceType' and 'Alcohol' are 'present' (value of 1).

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Alcohol Effect on Facial Attractiveness

The effect of alcohol on facial attractiveness ratings is stronger when the face is unattractive compared to when the face is attractive, suggesting an interaction effect between alcohol consumption and face type.

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Interaction Only When Both Predictors Are Active

The interaction effect is zero for all conditions except when both predictors are 'present'. This implies that the combined effect of both predictors is unique and distinct from their individual effects.

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Interaction as Benefit or Cost

The interaction effect represents the benefit or cost of having both variables present. It elucidates the unique effect of their combined presence beyond their individual effects.

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Interaction in the Study

In the study design, the interaction is measured as the difference between the effect of 'FaceType' on 'Attractiveness' when 'Alcohol' is present and the effect when 'Alcohol' is absent.

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Understanding Interactions

The interaction effect helps researchers understand how the effect of one variable changes depending on the levels of the other variable.

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Interaction and Main Effects

The interaction effect is not a separate effect but a modification of the main effects of the independent variables.

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Significance of Interaction

The interaction effect can be statistically significant even when the main effects are not significant.

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Analyzing Interaction Effects

Researchers use various methods, such as plotting interaction effects or conducting post-hoc tests, to further examine the interaction effect and understand its implications.

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Degrees of Freedom (df)

The number of independent pieces of information that are free to vary in the data. For example, in a group of participants, the degrees of freedom for computing a main effect is one less than the number of groups. This accounts for the fact that when calculating a mean, one value is determined by the others. This is why you often see df = g-1.

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Mean Sum of Squares (MS)

A statistic used to assess the variance between groups, reflecting the variability of group means around the grand mean. This is computed by dividing the total sum of squares (representing the variability) by the degrees of freedom.

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F-statistic

A statistical test used to compare the variances between groups. It calculates the ratio of two mean sums of squares, reflecting the relative sizes of group variances. This ratio can be interpreted by comparing the calculated F value with a critical F value from an F-distribution.

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Sum of Squares Between Groups (SSB)

The sum of squares of the deviations of each group mean from the grand mean, weighted by the number of participants in each group. This measure quantifies the variability between the groups.

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Total Sum of Squares (SSM)

The sum of squares representing the overall variation in the data. This includes both within-group variance and between-group variance.

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Sum of Squares Within Groups (SSR)

The sum of squares of the deviations of each observation from its respective group mean. This quantifies the variability within each group. It is a sum of individual group variances combined across each group.

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Partial η2

An effect size statistic that measures the proportion of variance in the dependent variable that is explained by the independent variable or interaction. A large partial η2 value indicates that the independent variable (or interaction) strongly influences the dependent variable.

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P-value (Sig.)

A measure of the statistical significance of an effect, indicating the probability of observing the effect if there is no real effect. A smaller p-value suggests stronger evidence against the null hypothesis, indicating a significant effect.

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Study Notes

Research Design and Statistics Lecture Notes

  • The lecture covered ANCOVA (Analysis of Covariance) and factorial independent ANOVA.
  • ANCOVA models a covariate using a linear model, linking it to regression and ANOVA.
  • Factorial independent ANOVA extends independent ANOVA to account for more than one categorical predictor variable.
  • The lecture includes a decision tree for choosing the correct statistical test based on data type and characteristics. This tree considers different types of measurements, numbers of predictors, types of predictor variable levels, and whether participants are the same or different for each level of predictors.
  • A model for more than two means, similar to a t-test model, was presented in ANOVA to account for multiple means.
  • An example dataset, "Puppies.sav", includes a control group and two treatment groups (15 minutes and 30 minutes of puppy contact). A measure of happiness was used as the dependent variable, with a covariate measuring the participant's love of puppies.
  • Dummy variables were used to represent the categorical predictor variable (doses of puppy therapy), allowing for accounting for the covariate's effect on the output.
  • ANCOVA assumptions include normality and homogeneity of variance (tested using Levene's test).
  • The covariate and treatment effects should be independent. Predictor variables should not correlate too much with one another for reliable outcome estimations. Regression slopes across different treatment groups (levels of the categorical variable) must be similar (homogeneity of regression slopes).
  • SPSS software was used for analyzing the data, with particular focus on the outcome variable, categorized predictor (dose of therapy) and the covariate (love of puppies).
  • Statistical output tables (e.g., "Tests of Between-Subjects Effects", "Adjusted Means") interpret the results and show the impact of the covariate after controlling for the effects of other variables (like the dosage of therapy).
  • The methods allow calculation of total, model, and residual sums of squares for different components (main effect for each predictor, interaction between the predictors), degrees of freedom, mean sums of squares, associated F-values, and the related effect size (partial n squared).
  • Levene's test of equality of error variances was discussed as a critical assumption check.
  • Factorial designs were reviewed, including independent, repeated measures, and mixed designs.
  • In an independent factorial design, different participants are used in different groups for the study
  • The impact of interactions between variables on the outcome was explored using a mathematical model and illustrated with charts.
  • Calculations for different kinds of sum of squares are explained: total sum of squares, model sum of squares, the main effect of face type sum of squares, the main effect of alcohol sum of squares, and interaction sums of squares. Calculations for residual sums of squares and mean sums of squares, and F-tests are shown.
  • Finally, specific calculations and how to interpret the results for the output were discussed to understand effect sizes.

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Description

This quiz covers key concepts from the lecture on ANCOVA and factorial independent ANOVA. It discusses the modeling of covariates and presents a decision tree for selecting the appropriate statistical tests based on data characteristics. Practical application is illustrated with an example dataset analyzing happiness based on puppy contact duration.

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