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Aug 4, 2017 10:00 AM
(831 views)

Hi,

I know that the topic of linear slope calculation has been discussed before but I could not find an efficient way to create a tabulated output of Slopes for a set of Cases (i.e. Patients) for which I have varying numbers of obervations as a function of time.

Here is a screen shot of the data (mock; the actual file is attached):

Following the advice of previous discussions in this board, I used the Fit Y by X (Change in Measure by Time) using Patient_ID as By variable, and plotting a linear fit with intercept constrains to 0:

Ouput: 5 analyses identical to the one below:

Where I'm stuck is how to collect the Estimate of the Slope into a new table that would look like:

Patient_ID | Slope |

AAA | m1 |

BBB | m2 |

CCC | m3 |

DDD | m4 |

EEE | m5 |

Any suggestion would be welcome: I'm not attached to the original data format or the analysis method.

Thanks

1 ACCEPTED SOLUTION

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Aug 4, 2017 10:42 AM
(1646 views)

Solution

You discovered the **By** role group the data for separate regression analysis. (I hope that you know to press and hold the Ctrl key before clicking the red triangle and selecting the Fit Line command!) Now right-click on the Parameter Estimates table and select Make Combined Data Table.

Learn it once, use it forever!

6 REPLIES

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Aug 4, 2017 10:30 AM
(827 views)

This code will do the trick. The "secret" is to look at the underlying tree structure of the output, converted to a report.

```
dt = data table("SLOPE_Calculation_mock_data");
bv = dt << Bivariate(
Y( :Change in Measure ),
X( :Time ),
Fit Line( {Line Color( {213, 72, 87} )} ),
By( :Patient_ID )
);
// Figure out how many patients there are
dtab = dt << Tabulate(
Show Control Panel( 0 ),
Add Table( Row Table( Grouping Columns( :Patient_ID ) ) ),
invisible
);
pdt = dtab << Make Into Data Table;
np = nrows(pdt);
patient_list = pdt:Patient_ID << get values;
dtab << close window;
pdt << new column("Slope", numeric, continuous);
bvrep = bv << report;
//bvrep << show tree structure; // Used to get underlying structure
for (i = 1, i <= np, i++,
parameter_estimates = bvrep[i][numbercolbox(7)] << get;
one_slope = parameter_estimates[2];
pdt:Slope[i] = one_slope;
);
```

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Aug 4, 2017 10:44 AM
(823 views)

Hi,

Thanks for your quick reply: it is what I was looking for with the exception that the "retrieval" of the parameter_estimate from the multi plot report does not work because the NumberColBox (7) only works for the first plot, the following plots have their corresponding NumberColBox 23, 37 and so on.

I'm not sure how to iterate through the NumberColBox call.

Any thoughts?

Thanks

TS

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Aug 4, 2017 11:19 AM
(812 views)

A script could extract the estimates, too, using several different techniques. The common iteration approach becomes cumbersome due to the By groups but can be straight-forward, if only brute force. A more elegant solution would use a single XPath query on the report display tree to retrieve all of thee slopes as a vector. I don't have time right now to research the exact syntax but it would be easy, details aside. Something like this:

`plat << XPath( "//NumberColBox[NumberColBoxHeader=\!"Estimate\!"]" ) << Get( 2 );`

Learn it once, use it forever!

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Aug 4, 2017 11:30 AM
(810 views)

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Aug 4, 2017 10:42 AM
(1647 views)

You discovered the **By** role group the data for separate regression analysis. (I hope that you know to press and hold the Ctrl key before clicking the red triangle and selecting the Fit Line command!) Now right-click on the Parameter Estimates table and select Make Combined Data Table.

Learn it once, use it forever!

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Aug 4, 2017 10:45 AM
(821 views)