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Created: Nov 19, 2016
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Week 13 Blood Pressure Systolic day vs Diastolic day
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Introduction

We are interested in evaluating diurnal variation in blood pressure in women who were normotensive and those with preeclampsia. The subjects are similar, age, weight, and mean gestation or 35 weeks. A total of 24 women in each groub. Both diastolic and systolic blood pressure was obtained at two time periods-day and night.

Method

The scatter plots from last week were linear so we need to proceed to regression analysis for both normotensive and preeclampsia groups. We willll look at our QQ plot with residuals first with the normotensive group.

Result 1: QQ BP 1203   [Info]
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We see by the QQ plot that we have normality. The scatter plot shown bellow has no evidence of a curve. 

Result 2: Fitted BP   [Info]
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Now we will look at the regression output for the normotensive group. (below). 

Result 4: 222   [Info]
Simple linear regression results:
Where: Group="Normotensive"
Dependent Variable: Systolic (day)
Independent Variable: Diastolic (day)
Systolic (day) = 46.565594 + 0.97524752 Diastolic (day)
Sample size: 24
R (correlation coefficient) = 0.68572187
R-sq = 0.47021449
Estimate of error standard deviation: 5.7269133

Parameter estimates:
ParameterEstimateStd. Err.DF95% L. Limit95% U. Limit
Intercept46.56559415.8600912213.67377879.45741
Slope0.975247520.22070164220.517540351.4329547

Analysis of variance table for regression model:
SourceDFSSMSF-statP-value
Model1640.41254640.4125419.5262390.0002
Error22721.5457932.797536
Total231361.9583

Predicted values:
X valuePred. Ys.e.(Pred. y)95% C.I. for mean95% P.I. for new
105148.966587.4490208(133.51826, 164.41491)(129.4804, 168.45277)

In the previous study done in week 12 we found the correlation was statistically significant for the normotensive group (r=0.69, p=0.0002).There is a moderately strong relationship between daytime systolic and diastolic BP in normotensive patients.

With 95% confidence we estimate the slope of our true regression line to be between 0.52 to 1.43. Meaning the slope represents that one BPM increase in daytime Diastolic BP will correspond to a 0.52 to 1.43 BPM increase in the average daytime systolic BP.

Result 3: Nonotensive   [Info]
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With 95% confidence in a patient who is normotensive who measured 105 BPM during the day for SBP will be some where between 129.48 to 168.45. 

 

Now we look at the Preeclampsia group. 

Result 5: QQ Preeclampsia   [Info]
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We see by the QQ plot that we have normality. The scatter plot shown bellow has no evidence of a curve.

 

Result 6: Predicted Preeclampsia   [Info]
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Now we will look at the regression output for the preeclampsia group.

 

Result 7: 12032   [Info]
Simple linear regression results:
Where: Group="Preeclampsia"
Dependent Variable: Systolic (day)
Independent Variable: Diastolic (day)
Systolic (day) = 50.972659 + 0.98854409 Diastolic (day)
Sample size: 24
R (correlation coefficient) = 0.79303388
R-sq = 0.62890273
Estimate of error standard deviation: 6.3200918

Parameter estimates:
ParameterEstimateStd. Err.DF95% L. Limit95% U. Limit
Intercept50.97265914.3925012221.12443980.820879
Slope0.988544090.16189627220.652791781.3242964

Analysis of variance table for regression model:
SourceDFSSMSF-statP-value
Model11489.24171489.241737.283648<0.0001
Error22878.7583339.943561
Total232368

Predicted values:
X valuePred. Ys.e.(Pred. y)95% C.I. for mean95% P.I. for new
105154.769792.9604228(148.63025, 160.90933)(140.29605, 169.24353)

In the previous study done in week 12 we found the correlation was statistically significant for the preeclampsia  group (r=0.79, p=<0.001).There is a moderately strong relationship between daytime systolic and diastolic BP in preeclampsia patients.

 With 95% confidence we estncrease in the average day Diastolic BP in the preeclampsia group.imate the slope of our true regression line to be between 0.65 to 1.32. Meaning the slope represents that one BPM increase in daytime Diastolic BP will correspond to a 0.65 to 1.32 BPM increase in the average daytime systolic BP in the preeclampsia group. 

Result 8: Prediction Preeclampsia   [Info]
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With 95% confidence in a patient with preeclampsia who measured 105 BPM during the day for SBP will be some where between 140.29 to 169.24.

Conclusion

The results in general suggest patients with preeclampia has a greater SBP and DBP in the morning in general. While we can see the higher/lower SBP vs DBP is in normotensive vs. preeclampsia patients we know that there will always be a difference in SBP vs DBP in patients. A further study should be done of night vs day BP in the 2 groups. One could also look at the diets and or medications these individuals are one to help control blood pressure. 

 

 

 

 

HTML link:
<A href="https://www.statcrunch.com/5.0/viewreport.php?reportid=65019">Week 13 Blood Pressure Systolic day vs Diastolic day</A>

Comments
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By nku.katie.waters
Nov 27, 2016

Hi Jessica,
I scanned quickly through your report and didn’t notice anything that was in obvious need of substantial improvement. But here are a couple things to keep in mind that may apply to your report:
1. For the preeclampsia group, a correct interpretation of the slope: With 95% confidence, we estimate the slope of our true regression line to be between 0.66 and 1.36. Putting this in context of the problem, we can say that a one BPM increase in daytime Dystolic BP will correspond to a 0.66 to 1.36 BPM increase in the AVERAGE daytime Systolic BP for preeclampsia women. (We would interpret the slope for the normotensive group similarly.)

2. You were asked to make some predictions of your choosing which is done by selecting "Prediction of Y" and entering a value for X when conducting the Linear Regression procedure. For example, if we wish to make an individual prediction for X=80, a correct interpretation would be: For a preeclampsia individual with 80 bpm daytime Dystolic BP, the estimated daytime SBP is between 115.7 and 143.8 bpm. Remember that a PI is interpreted for an INDIVDUAL – not average.

3. There is one outlier that you should remove from your dataset because it is an impossible value. Removing the outlier will change your regression results. See solutions.
By karissa.neidig
Nov 20, 2016

Good job on your report! All your scatter plots look great as well as your simple linear regression. I agree that looking at other factors, especially the patient's medications would be important to see how it affects their blood pressure.

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