Levene's test ( Levene 1960) is used to test if k samples have

**equal variances**.**Equal variances**across samples is called homogeneity of**variance**. Some statistical tests, for example the analysis of**variance**, assume that**variances**are**equal**across groups or samples. The Levene test can be used to verify that**assumption**.What does it mean to assume equal variance?

Statistical tests, such as analysis of

**variance**(ANOVA),**assume**that although different samples can come from populations with different**means**, they have the same**variance**.**Equal variances**(homoscedasticity) is when the**variances**are approximately the same across the samples.1

## What is unequal variance?

When you choose to compare the means of two nonpaired groups with a t test, you have two choices: Use the standard unpaired t test. It assumes that both groups of data are sampled from Gaussian populations with the same standard deviation. Use the

**unequal variance**t test, also called the Welch t test.2

## What is meant by homogeneity of variance?

The assumption of

**homogeneity of variance**is that the**variance**within each of the populations is equal. This is an assumption of analysis of**variance**(ANOVA). ANOVA works well even when this assumption is violated except in the case where there are unequal numbers of subjects in the various groups.3

## Why do we test for equal variance?

Use a

**test for equal variances**to**test**the equality of**variances**between populations or factor levels. Many statistical procedures, such as analysis of**variance**(ANOVA) and regression, assume that although different samples can come from populations with different means, they have the same**variance**.4

## How do you know if you have equal variance?

**If**the

**variances**are relatively

**equal**, that is one sample

**variance**is no larger than twice the size of the other, then you can

**assume equal variances**. By looking at the output of the Levene's test you decide which row to use.

**If**the significance is .05 or below, use the bottom row, or “

**equal variances**not

**assumed**.”

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## What does two sample equal variance mean?

Assuming

**Equal**.**Variance**(Enter Means) Introduction. This procedure provides**sample**size and power calculations for one- or**two**-sided**two**-**sample**t-tests when the**variances**of the**two**groups (populations) are assumed to be**equal**. This is the traditional**two**-**sample**t-test (Fisher, 1925).6

## What are the assumptions of an Anova?

**The Wikipedia page on ANOVA lists three assumptions, namely:**

- Independence of cases – this is an assumption of the model that simplifies the statistical analysis.
- Normality – the distributions of the residuals are normal.
- Equality (or "homogeneity") of variances, called homoscedasticity

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## What is meant by a variance?

The

**variance**measures how far each number in the set is from the**mean**.**Variance**is calculated by taking the differences between each number in the set and the**mean**, squaring the differences (to make them positive) and dividing the sum of the squares by the number of values in the set.8

## What is the assumption of independence?

The

**assumption of independence**is a foundation for many statistical tests. The**assumption of independence**is used for T Tests, in ANOVA tests, and in several other statistical tests. The observations between groups should be**independent**, which basically**means**the groups are made up of different people.9

## What is the variance of a population?

In probability theory and

**statistics**,**variance**is the expectation of the squared deviation of a random variable from its mean. Informally, it measures how far a set of (random) numbers are spread out from their average value.10

## What is the meaning of homogeneity?

In statistics,

**homogeneity**and its opposite,**heterogeneity**, arise in describing the properties of a dataset, or several datasets. They relate to the validity of the often convenient assumption that the statistical properties of any one part of an overall dataset are the same as any other part.11

## What is the meaning of Homoscedasticity?

**Homoscedasticity**. This assumption means that the variance around the regression line is the same for all values of the predictor variable (X). The plot shows a violation of this assumption. For the lower values on the X-axis, the points are all very near the regression line.

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## What is Bartlett's test for?

Equal variances across samples is called homogeneity of variances. Some statistical

**tests**, for example the analysis of variance, assume that variances are equal across groups or samples. The**Bartlett test**can be used to verify that assumption.**Bartlett's test**is sensitive to departures from normality.13

## What does an independent samples t test tell you?

The

**Independent Samples t Test**compares the means of two**independent**groups in order to determine whether there is statistical evidence that the associated population means are significantly different. The**Independent Samples t Test**is a parametric**test**. This**test**is also known as:**Independent t Test**.14

## What does sphericity mean?

**Sphericity**is an important assumption of a repeated-measures ANOVA. It refers to the condition where the variances of the differences between all possible pairs of within-subject conditions (i.e., levels of the independent variable) are equal.

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## What is the partial eta squared for?

**Eta squared**measures the proportion of the total variance in a dependent variable that is associated with the membership of different groups defined by an independent variable.

**Partial eta squared**is a similar measure in which the effects of other independent variables and interactions are partialled out.

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## What is sphericity in geology?

**Sphericity**is the measure of how closely the shape of an object approaches that of a mathematically perfect sphere.

**Sphericity**applies in three dimensions; its analogue in two dimensions, such as the cross sectional circles along a cylindrical object such as a shaft, is called roundness.

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## Why are rocks smooth and round?

Abrasion-

**Rocks**collide causing the**rocks**to chip and become**smooth**. resistance- the sand creates resistance and acts like sand paper to**smooth**the**rocks**. motion of the water- The motion of the water pushes the**rocks**and causes the**rocks**to collide with the**rocks**and stream beds.