# z-score used as X axis variable

#### Nayomi James

##### New Member
Seeking your opinion on the use of z-scores instead of original data for a correlation graph.
I have a paper showing a graph of two factors, that should correlate because the authors state that the multiple regression result shows that only variable X data explains changes in Y data.
However, instead of plotting the actual X data the authors have chosen to plot the z-scores. Would z-scores exaggerate the change in X values so the graph of the relationship with Y appears more convincing? Even on this graph it looks like the regression line is being riven by three extreme points, while the remaining 20 points appear completely random.
Nayo

#### Nayomi James

##### New Member
This is what I want to see and would be grateful for confirmation if this is a logical request.
The graph of variable X vs variable Y with the regression line calculated from the least squares of the residuals.
Please let me know what you think,
Nayo

#### hlsmith

##### Not a robit
Was the variable standardized in the multiple regression model - a standard deviation change in X associated with a ?? change in Y?

Also, I agree with @Buckeye - provide link to "paper".

#### Nayomi James

##### New Member
Hi Buckeye and hlsmith,
Thank you for your supportive replies. Sadly I am not permitted to post their graph at this time. I have attached a very similar graph. The Y axis has straightforward raw data plotted. The X axis has the z-scores of the other variable plotted on a scale from -2 standard deviations through zero to +2 SD. To answer your question, yes, the authors state this variable is standardised. Ten data points fall within the confidence intervals lines for the regression line, thirteen outside. The image I have attached is very similar in the spread of data.
The results section consists of two sentences. The first states multiple regression was used to evaluate the association between X and Y. The second gives the results showing a statistically significant positive relationship between X and Y values and that other factors did not contribute to the equation. I have no problem with the use of scatter plots with the regression line and confidence intervals. What I query is plotting the z-scores without explanation in the text or in the legend that accompanies the graph.
I really appreciate your time in considering this. I look forward to your advice.
Nayo

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#### Nayomi James

##### New Member
Correction: The authors state the variable X is standardised for the graph, but not for the regression.

#### hlsmith

##### Not a robit
Are you peer reviewing this paper? Yeah it could be confusing changing scale and a better description and labeling is probably needed. I can't remember the term, but I believe standardizing data is a "monotonic" transformation meaning it does change result when viewing conclusions. I would like to confirm that, I can't think why the results would differ! Though remember I am not providing any citations!!!

#### Nayomi James

##### New Member
Dear hlsmith,
Yes and thank you I have added comments appropriate for your suggestion. Have a great week.
Kindest regards,
Nayo