What is the primary purpose of an A/B test?
To compare a control version of a system ('A') with a modified treatment version ('B') to see which performs better on key metrics.
In A/B testing, what is the 'control' group, often labeled 'A'?
It is usually the current system and is considered the 'champion' against which modifications are tested.
In statistics, what is a theoretical construct?
The abstract concept or thing you are trying to measure, such as 'age', 'gender', or an 'opinion', which cannot be directly observed.
The process by which a vague concept is turned into a precise measurement is known as _____.
operationalisation
What is the key characteristic of a nominal scale variable?
The different possibilities are distinct categories with no intrinsic order or ranking between them (e.g., eye color).
How does an ordinal scale variable differ from a nominal scale variable?
An ordinal scale variable has a natural, meaningful order to its possibilities, but the differences between them are not necessarily equal (e.g., finishing position in a race).
What distinguishes an interval scale variable from an ordinal scale variable?
The differences between the numbers are interpretable and equal, but there is no 'natural' zero value (e.g., temperature in Celsius).
The reliability of a measure tells you how _____ you are measuring something.
precisely
The validity of a measure tells you how _____ the measure is.
accurate
What does test-retest reliability assess?
It assesses consistency over time by seeing if repeating the measurement at a later date yields the same answer.
What is a confounder in research?
An additional, often unmeasured variable that is related to both the predictors and the outcome, threatening internal validity.
A research result is said to be _____ if it only holds in the special situation that was tested, threatening its external validity.
artefactual
What does a positive kurtosis value indicate about a distribution's shape?
It indicates a more 'pointy' distribution with heavy (longer) tails.
What does a negative kurtosis value indicate about a distribution's shape?
It indicates a more uniform or flatter distribution with light (shorter) tails.
What is the purpose of a Q-Q (quantile-quantile) plot?
To visually assess if a set of data comes from a normal distribution.
In a Q-Q plot, how do you know if the data is normally distributed?
The points will fall on or close to the 45-degree reference line.
What is an effect size?
A statistical measure used to determine the strength of the relationship or difference between variables.
Unlike a p-value, what can an effect size be used for?
It can be used to quantitatively compare the results of different studies.
What assumption is checked by the Shapiro-Wilk test?
The assumption of normality.
What is the non-parametric equivalent of a one-sample t-test for dichotomous categorical data?
The Binomial Test.
What is the purpose of a Multinomial Test?
It tests whether the sample frequency of a categorical variable with three or more factors is statistically different from a hypothesized population frequency.
What is the non-parametric equivalent for a paired samples t-test if data is not normally distributed?
The Wilcoxon's signed-rank test.
What does correlation analysis measure?
It determines if, and how strongly, pairs of quantifiable variables are associated or co-vary.
When should Spearman's (rho) or Kendall's (tau) correlation be used instead of Pearson's (r)?
When the data violate assumptions of normality and/or variance, or if the data is ordinal.
In linear regression, what does the $R^2$ value represent?
It represents the proportion of the variance in the outcome variable that can be accounted for by the predictor(s).
What does the Durbin-Watson statistic check for in a regression analysis?
It checks for correlations between residuals, which can invalidate the test.
What is the key difference between simple linear regression and multiple regression?
Simple regression uses one predictor variable, while multiple regression uses two or more predictor variables.
In logistic regression, what does an odds ratio of greater than 1 suggest?
It suggests a positive relationship, where an increase in the predictor is related to an increased probability of the outcome.
Why are post hoc tests necessary after a significant ANOVA result?
To determine exactly where the significant differences lie between the multiple group means.
What is the main assumption of a one-way independent ANOVA regarding the dependent variable?
The dependent variable should be approximately normally distributed and continuous.
What does Levene’s test assess in the context of an ANOVA?
It tests the null hypothesis that the variances in different groups are equal (homogeneity of variance).
What is the non-parametric equivalent of a one-way independent ANOVA?
The Kruskal-Wallis test.
What does the assumption of 'sphericity' relate to in a repeated measures ANOVA (RMANOVA)?
It relates to the equality of the variances of the differences between levels of the repeated measures factor.
What is the purpose of an ANCOVA?
To compare the 'adjusted' means of a dependent variable between two or more groups while controlling for the effect of other continuous variables (covariates).
What key assumption, tested by looking at the interaction between the factor and the covariate, is important in ANCOVA?
The assumption of homogeneity of regression slopes.
What type of factors are involved in a Mixed Factor ANOVA?
It involves at least one between-subjects (independent) factor and at least one within-subjects (repeated measures) factor.
What does a Chi-Square test of independence evaluate?
It compares the observed frequencies in a contingency table with the frequencies that would be expected if there was no association between the two categorical variables.
A key validity rule for a chi-square test is that less than 20% of cells should have an expected count of less than _____, and none less than 1.
5
What is the primary purpose of a meta-analysis?
To statistically integrate results from multiple studies, providing a single numerical value of the overall treatment effect.
In meta-analysis, what does the term 'heterogeneity' describe?
It describes any clinical, methodological, or statistical variability that may exist between the different studies included in the analysis.
What is the difference between experimental and non-experimental research?
In experimental research, the researcher controls and manipulates variables, while in non-experimental research, the researcher observes phenomena as they naturally occur.
What is the primary threat to the internal validity of a study?
The presence of confounders, which are unmeasured variables related to both the predictors and the outcome.
What does construct validity assess?
It assesses whether you are actually measuring the theoretical construct that you intend to be measuring.
The _____ effect refers to the possibility that specific external events may occur during a study that might influence the outcome measure.
history
What are maturation effects in a research study?
Changes in participants that occur naturally over time, such as getting older, tired, or bored, which can influence the outcome.
The phenomenon where experimenters, despite best intentions, accidentally influence results by subtly communicating the 'right answer' to participants is called _____.
experimenter bias
What is the 'placebo effect'?
A specific type of demand effect where the mere belief of being treated causes an improvement in outcomes, rather than the treatment itself.
What is the key difference between a sample and a population?
A sample is the finite, incomplete set of observations available, whereas a population is the abstract, entire set of all possible observations you want to draw conclusions about.
A procedure in which every member of the population has the same chance of being selected is called a _____.
simple random sample
What does the law of large numbers state?
It states that as a sample size grows, its mean will get closer and closer to the average of the whole population.
What is a sampling distribution of the mean?
It is the probability distribution of sample means that would be obtained by drawing all possible samples of a particular size from a population.
The _____ states that for a large enough sample size, the sampling distribution of the mean will be approximately normal, regardless of the population distribution.
central limit theorem
Why is the sample standard deviation (dividing by $N$) considered a biased estimator of the population standard deviation?
It is systematically smaller, on average, than the true population standard deviation, especially for small samples.
To get an unbiased estimate of the population variance, one should divide the sum of squared deviations by _____.
$N-1$
What is the correct interpretation of a 95% confidence interval?
If we were to repeat the experiment many times, 95% of the calculated confidence intervals would contain the true population parameter.
The standard deviation of a sampling distribution is referred to as the _____.
standard error
In hypothesis testing, what is the null hypothesis ($H_0$)?
A statistical hypothesis corresponding to the exact opposite of what the researcher wants to believe, often stating there is no effect or no difference.
What is a Type I error in hypothesis testing?
Rejecting the null hypothesis when it is actually true.
What is a Type II error in hypothesis testing?
Retaining (failing to reject) the null hypothesis when it is actually false.
The probability of making a Type I error is denoted by the Greek letter _____.
$\alpha$ (alpha)
The power of a test, denoted as $1 - \beta$, is the probability of what?
The probability of correctly rejecting the null hypothesis when it is false.
What does the p-value represent in Neyman's approach to hypothesis testing?
It represents the smallest Type I error rate ($\alpha$) at which you would have to be willing to tolerate in order to reject the null hypothesis.
What is a common but incorrect interpretation of the p-value?
That it is 'the probability that the null hypothesis is true'.
What is the purpose of the chi-square goodness-of-fit test?
It tests whether an observed frequency distribution of a nominal variable matches an expected or theoretical frequency distribution.
The degrees of freedom for a chi-square goodness-of-fit test with $k$ categories is _____.
$k-1$
What type of data is required for a chi-square test of independence?
Two categorical variables, organized into a contingency table (cross-tabulation).
What is the formula for calculating the degrees of freedom in a chi-square test of independence with $r$ rows and $c$ columns?
$(r-1)(c-1)$
Which effect size measure is commonly used for chi-square tests and gives a value between 0 (no association) and 1 (perfect association)?
Cramér's V.
What is the main difference in assumptions between the Student's t-test and the Welch's t-test for independent samples?
The Student's t-test assumes homogeneity of variance (equal standard deviations), while the Welch's t-test does not.
A paired-samples t-test is mathematically equivalent to performing what other test?
A one-sample t-test on the difference scores between the paired observations.
Which effect size is most commonly used for a t-test?
Cohen's d.
What is an interaction effect in a factorial ANOVA?
It occurs when the effect of one factor is different depending on the level of another factor.
If the lines on a descriptive plot for a two-way ANOVA are not parallel, what might this suggest?
It suggests a possible interaction effect between the two factors.
What does a significant result from Mauchly’s test of sphericity indicate?
It indicates that the assumption of sphericity has been violated and a correction (e.g., Greenhouse-Geisser) should be applied to the F-value.
What is the purpose of a Bonferroni correction?
To adjust p-values when performing multiple statistical tests to control the family-wise Type I error rate.
The _____ correction is a method for multiple comparisons that is generally more powerful than the Bonferroni correction while maintaining the same Type I error rate.
Holm
According to the Kohavi and Thomke article, what percentage of experiments at Google and Bing typically generate positive results?
Only about 10% to 20%.
What is the term for the counter-intuitive situation where a trend that appears in several groups of data disappears or reverses when these groups are combined?
Simpson's paradox.
What is the difference between a discrete and a continuous variable?
A continuous variable can take any value within a range, while a discrete variable has a finite or countable set of possible values.
A _____ plot visualizes the distribution of data over a continuous interval, using kernel smoothing to create a smooth curve.
density
In a box plot, the thick line in the middle of the box represents the _____.
median
In a box plot, observations that fall outside the range of the 'whiskers' are typically referred to as _____.
outliers
What view defines probability as a 'long-run frequency' of an event?
The frequentist view.
The _____ view of probability defines the probability of an event as the 'degree of belief' that a rational agent assigns to its truth.
Bayesian
The _____ distribution is used for modeling the number of successes in a fixed number of independent trials with a constant probability of success.
binomial
What is the most important property of the normal distribution in statistics?
It is described by its mean ($\mu$) and standard deviation ($\sigma$), and it forms the basis for the central limit theorem.
What is the primary characteristic of a one-sided hypothesis test?
The alternative hypothesis specifies the direction of the effect (e.g., $\mu > \mu_0$ or $\mu < \mu_0$), so the critical region is in only one tail of the distribution.
In Bayesian hypothesis testing, what does the Bayes factor (BF) quantify?
It quantifies the strength of evidence provided by the data in favor of one hypothesis over another.
The total sum of squares ($SS_{tot}$) can be partitioned into the _____ sum of squares ($SS_b$) and the _____ sum of squares ($SS_w$).
between-group; within-group
In ANOVA, the test statistic is the ratio of the between-groups mean square ($MS_b$) to the within-groups mean square ($MS_w$), which is known as the _____.
F-ratio
In the context of research design, what does 'reactivity' refer to?
The phenomenon where participants' behavior changes simply because they are aware they are being studied.
The problem in regression where predictor variables are too strongly correlated with each other is known as _____.
collinearity
In regression diagnostics, an observation that is very different from what the model predicts and has a large Studentised residual is called an _____.
outlier
What is a 'high leverage' point in a regression analysis?
An observation that is very different from other observations in terms of its predictor variable values.
An observation that is both an outlier and has high leverage is known as a _____ observation because it can have a big effect on the regression line.
high influence
In JASP, which menu would you use to find the chi-square test of independence?
Frequencies > Contingency Tables.
In JASP, how can you create a new variable based on a calculation involving other variables?
Click the plus sign (+) at the end of the data columns to open the 'Create Computed Column' dialog.
The non-parametric alternative to a repeated measures ANOVA is _____.
Friedman’s test
What does a 'main effect' refer to in a factorial ANOVA?
The effect of one independent variable on the dependent variable, averaging across the levels of the other independent variable(s).
Which type of sum of squares (Type I, II, or III) is generally recommended for unbalanced factorial ANOVA designs because its tests do not depend on the order in which factors are entered?
Type III sum of squares.
In the context of JASP and other statistical software, what type of file format uses a `.csv` extension?
Comma Separated Value file.
The problem of researchers running every possible analysis, finding one that works, and then pretending it was the only one they conducted is known as _____.
unacknowledged data mining
What is publication bias?
The tendency for journals to prefer publishing studies that find a 'significant' effect over those that find 'null' results, leading to a skewed representation of evidence.
What does the mean absolute deviation (MAD) measure?
It measures the average distance between each data value and the mean of the data set.
The _____ of a data set is defined as the average of the squared deviations from the mean.
variance
What is the relationship between standard deviation and variance?
The standard deviation is the square root of the variance.
In JASP's Correlation Matrix output, what does Pearson's r measure?
It measures the strength and direction of the linear relationship between two continuous variables.
If a regression model is completely useless, its $R^2$ value would be equal to _____.
0
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