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Psychology Notes Statistics (2nd year) Notes

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Updated Revision Notes Stats Notes

Statistics (2nd year) Notes

Statistics (2nd year)

Approximately 18 pages

The notes give details on how to select the correct statistical test out of:
1 way independent ANOVA
2 way independent ANOVA
Repeated measures ANOVA
Mixed ANOVA
Regression (Stepwise)
Factor Analysis (PCA)

The notes provide clear instructions for how to carry out the statistical tests on SPSS, stating exactly what to press on the programme, as well as a step-by-step guide of how to interpret the SPSS output....

The following is a more accessible plain text extract of the PDF sample above, taken from our Statistics (2nd year) Notes. Due to the challenges of extracting text from PDFs, it will have odd formatting:

GENERAL

4 questions, 1 each on:

2 way independent ANOVA

Mixed ANOVA

Regression (Stepwise)

Factor Analysis (PCA)

You will have to work out the diff between 2 way and mixed ANOVA regression and PCA will say

One or Two-Way Independent ANOVA Used to study differences in group means (along with interaction effects)
Multiple regression Used to study relationship between variables (whether certain variables predict an outcome variable)
Factor analysis Used to explore whether they is any meaningful pattern in data (no p values)
Repeated Measures (RM) ANOVA

Used when there are more data points than Ps

And when you have 1 or more IV in a RM design

Mixed ANOVA Used when you have some IV(s) which are of ind design, and some IV(s) which are RM design

Which ANOVA?

Ask:

What are the IVs? What is the DV?

How many IVs are there?

How many conditions of each IV?

Between subjects, within subjects, or both?

  1. = small effect size

0.06 = medium effect size

0.14 = large effect size

Case:Variable 25:1, preferably 40:1

Checks for multicollinearity

A tolerance statistic of less than 0.1 is a serious problem

A tolerance statistic of less than 0.2 is a potential problem

Post hoc tests (work similar to t tests)

= tells us the direction of the differences between groups

  • If the main effect from the omnibus test is not sig you do not need to do any post hoc tests

  • If the main effect of the omnibus test is sig we do need to follow up with post hoc tests

Write out all descriptive stats just copy out SPSS table

ONE-WAY INDEPENDENT ANOVA

= when IVs are in groups/conditions

= determines differences between groups when you have more than 2 conditions

SPSS instructions:

Analyse Compare mean 1-way ANOVA

IV in Factor box

DV in dependent list

Options select

  • Descriptive

  • Homogeneity of variance test

  • Welch ( test which corrects for unequal variance)

  • Means plot

Post Hoc select

  • Scheffe

  • Games-Howell

Continue OK

Step 1

Is the data suitable for a one way independent ANOVA?

More than 2 conditions

One nominal IV (more than 2 groups or categories)

One interval/ratio DV (on a continuous scale)

Step 2

Is the sample suitable for a one way independent ANOVA?

Roughly equal group sizes largest group size should be no more than twice the smallest group size

At least 30 cases in total

At least 10 cases in each group

(If you fewer cases than this, still run an ANOVA, just mention to be cautious about interpretation. If p values are in the region of .05 to .10, and/or the effect size is large, it is more likely that the result is not significant purely because of a lack of statistical power).

Step 3

Are there equal variances between the groups?

Check the Levene’s statistic.

If not significant, groups have equal variance use the table which reports the standard F statistic.

If significant, it indicates that the groups differ significantly in their variance (ie unequal variance) use the table with Welch’s F statistic.

Step 4

What do the results of the overall ANOVA tell us?

Report: F(df1, df2) = _ , p = _ , η² = _

η² = eta squared (the effect size). In the exam just write ‘eta squared’.

Eta squared = (Between groups Ps) / (Total Ps) x100 to get %

Interpret: Was the p value significant? What was the effect size? Is this a small/medium/large effect? the p needs to be less than 0.05 to be sig

Step 5

Run post hoc tests (if the main effect of the ANOVA is significant)

If the Levenes test was not significant: Use the Scheffe test

If the Levenes test was significant: Use the Games-Howell test

Report mean scores for the groups

Look at p values from post hoc tests Interpret these ie if sig or not

TWO-WAY INDEPENDENT ANOVA

= when IVs are in groups/conditions

= more than 1 IV

SPSS instructions:

Analyse General Linear Model Univariate

IV in Factor box

DV in dependent list

Plots select

  • Put first IV in horizontal axis

  • Put other IV in separate lines

  • Add

  • Do the same but reverse variables

  • OK

Options

  • Move all factors from L to RH side into ‘display means for’ box

From display section choose

  • Descriptive stats

  • Estimates of effect size

  • Homogeneity tests

Post Hoc

  • Select both variables from Factors box put into Post Hoc Tests for box

  • Scheffe

  • Continue OK

Step 1

Is the data suitable for a Two Way independent ANOVA?

More than 1 nominal IV (2 groups or more per IV)

1 interval/ratio DV (on a continuous scale)

Step 2

Report descriptive statistics (means, standard deviations) for each subgroup

Step 3

Is the sample suitable for a Two way independent ANOVA?

Roughly equal group sizes largest group size should be no more than twice the smallest group size

At least 30 cases in total

At least 10 cases in each group

(If you fewer cases than this, still run an ANOVA, just mention to be cautious about interpretation. If p values are in the region of .05 to .10, and/or the effect size is large, it is more likely that the result is not significant purely because of a lack of statistical power)

Step 4

Are there equal variances between the groups?

Check the Levene’s statistic.

If not significant, groups have equal variance use the table which reports the standard F statistic.

If significant, it indicates that the groups differ significantly in their variance (ie unequal variance) use the table with Welch’s F statistic.

Step 5

What do the main effects of the ANOVA tell us?

Report: F(df1, df2) = _ , p = _ , η² = _ for each main effect

η² = partial eta squared (the effect size). In the exam just write ‘eta squared’ SPSS calculates this

Interpret: Was the p value significant? What was the effect size? Is this a small/medium/large effect? the p needs to be less than 0.05 to be sig

What does the interaction effect tell us?

Report: F(df1, df2) = _ , p = _ , η² = _

Interpret: Was the p value significant? What was the effect size? Is this a small/medium/large effect?

Step 6

The next step will depend on the results of the main effects and interaction effect:

Significant main effects?

  • YES: Interpret the direction of the main effects (use the mean scores ignoring...

Buy the full version of these notes or essay plans and more in our Statistics (2nd year) Notes.