power analysis: one-way anova user...

InVivoStat User Guides – Power Analysis: One-way ANOVA Version 4.0 December 2019

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Power Analysis:

One-way ANOVA

User Guide


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Contents

1 Introduction ......................................................................................... 3

2 Analysis procedure .............................................................................. 4 2.1 User based inputs ...................................................................................................................... 4

2.1.1 Select the analysis module ................................................................................................ 4 2.1.2 Select the group means ..................................................................................................... 4 2.1.3 Select the variability estimate ........................................................................................... 5 2.1.1 Significance level ............................................................................................................. 5 2.1.2 Defining the plotting range ............................................................................................... 5 2.1.1 Run the analysis ................................................................................................................ 5

2.2 Dataset based inputs ................................................................................................................. 6 2.2.1 Select the analysis module ................................................................................................ 7 2.2.2 Select the dataset to be analysed ....................................................................................... 7 2.2.3 Select the response to analyse and the treatment factor .................................................... 7 2.2.4 Select a transformation for the response ........................................................................... 8 2.2.5 Significance level ............................................................................................................. 8 2.2.6 Defining the plotting range ............................................................................................... 8 2.2.7 Run the analysis ................................................................................................................ 9

3 Output results ...................................................................................... 9

4 Controlling the output ...................................................................... 10

5 Test dataset example output ............................................................ 12 5.1 InVivoStat options (dataset based inputs)............................................................................... 12 5.2 Sample output ......................................................................................................................... 13


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1 Introduction

The Power Analysis modules in InVivoStat are available from the Statistics drop-

down menu entitled ‘Power Analysis’. Methods available include power analyses for

the two-sample t-test (comparison of means) and the overall one-way ANOVA. This

user guide describes the power analysis for the overall one-way ANOVA – powering

for the test of an overall difference between the treatment group means.

There are two interfaces available, depending on how the inputs to the power analysis

are generated:


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2 Analysis procedure

2.1 User based inputs

The steps required to perform an analysis using the user based inputs are described in

this section.

The inputs to the power analysis module include a measure of the variability (standard

deviation or variance), the treatment group means, and the choice of sample size

range. With the ‘user-based inputs’ sub-module, these are all entered manually by the

user.

2.1.1 Select the analysis module

The analysis begins by selecting the

Power Analysis: One-way ANOVA

(User based inputs) from the drop-down

list of available modules:

Power Analysis →

One-way ANOVA →

User based inputs

2.1.2 Select the group

means

Once the dataset has been selected, the

user selects the parameters for the

analysis by clicking on the boxes and

entering values of their choice.

The group means are entered as a

comma separated list.


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2.1.3 Select the variability

estimate

The user should enter an estimate of the

variability, either the standard deviation

or variance can be entered.

The variance estimate can be obtained

from an ANOVA table (the Mean

Square Error).

2.1.1 Significance level

The significance level default is 0.05, or

5%, although this can be changed.

2.1.2 Defining the plotting

range

Part of the output from the power

analysis module is a plot of a set of

power curves. The user can choose the

range of the X-axis (sample size) and

the Y-axis (statistical power) of this

plot.

2.1.1 Run the analysis

Click ‘Submit’ to run the analysis.


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2.2 Dataset based inputs

The steps required to perform an analysis using dataset based inputs are described in

this section.

This version of the One-way ANOVA power analysis module calculates the

variability directly from a dataset. InVivoStat will estimate the variability of a given

response by including a single treatment factor to account for any variability caused

by the treatment effects.

The analysis module accepts data in the single measures format, for example:

Response Treatment

1.17 D0

1.30 D0

1.72 D0

1.17 D0

1.39 D0

1.44 D0

1.60 D0

1.37 D1

1.64 D1

1.53 D1

1.50 D1

1.59 D1

1.77 D1

1.86 D1

1.26 D1

1.64 D1

1.26 D10

1.80 D10

1.19 D10

1.37 D10

1.44 D10

1.92 D10

1.37 D10

1.50 D10

2.06 D3

2.18 D3

1.99 D3

1.69 D3

1.62 D3

2.48 D3


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2.2.1 Select the analysis module

The analysis begins by selecting the

Power Analysis: One-way ANOVA

(Dataset based inputs) module from the

drop-down list of available modules:

Power Analysis →

One-way ANOVA →

Dataset based inputs

2.2.2 Select the dataset to be

analysed

Once the module is selected, the dataset

is chosen from the drop-down list of

available datasets.

Click ‘Submit’.

2.2.3 Select the response to

analyse and the treatment factor

Once the dataset has been selected, the

user can select the response variable for

the analysis by clicking on the Response

box and selecting the response to

analyse.

Similarly the user should select the

treatment factor.


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2.2.4 Select a transformation

for the response

Once selected, the user has the option of

applying a transformation to the

response variable, either log10, loge,

square root, arcsine or rank.

2.2.5 Significance level

The significance level default is 0.05, or

5%, although this can be changed.

2.2.6 Defining the plotting

range

Part of the output from the power

analysis module is a plot of a set of

power curves. The user can choose the

range of the X-axis (sample size) and

the Y-axis (statistical power) of this

plot.


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2.2.7 Run the analysis

Click ‘Submit’ to run the analysis.

3 Output results

The output contains the following.

Power curve plot

For the given parameters/variables entered in the module, InVivoStat generates a

power curve to illustrate the relationship between sample size, statistical power and

biologically relevant effect (for a given significance level).

Selected results

A set of summary power analysis results.

Definitions

A set of definitions is given to aid interpretation of the results.

References

A list of references for the methods applied in the analysis.


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4 Controlling the output

The user has the ability to control various aspects of the output. These are available in

the ‘Output Options’ dialogue:

Users can manipulate various plot

characteristics including line size, fonts

and marker size/type.


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The user has control over all text

included on the plots, for example text

position, size and font.

The user has control over the colour

scheme employed by InVivoStat,

including an option to produce all plots

in black & white.

Further information on these options can be found in the Getting Started User Guide.


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5 Test dataset example output

5.1 InVivoStat options (dataset based inputs)


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5.2 Sample output


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