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Created: Nov 19, 2017
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DIastolic BP- Linear Regression
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Introduction:  

This study examined the blood pressure during the day in women who had normal blood pressure and then those that had preeclampsia.  All of the participants were similar in age, weight, and mean duration of gestation (35 weeks). The researchers collected both systolic and diastolic BP readings during the day and at night. We will focus on systolic blood pressures during the day and the night.

Methods:  

Researchers analyzed similar women. The Diastolic and Systolic BP's were recorded for a normotensive group and a preeclampsia group.  

Analysis: The data we were given is interval/ratio data, which is appropriate for Pearson correlation. The 1st thing we must do in order to determine if there is a relationship between the systolic blood pressure during the day and at night is to produce a scatter plot.

One way anova was done to see if there was a relationship between the groups. The p value of

Analysis of Variance results:
Data stored in separate columns.

Column statistics

Column

n

Mean

Std. Dev.

Std. Error

Diastolic (day)

48

80.104167

10.929639

1.5775575

Diastolic (night)

48

67.041667

16.150829

2.3311714


ANOVA table

Source

DF

SS

MS

F-Stat

P-value

Columns

1

4095.0938

4095.0938

21.535766

<0.0001

Error

94

17874.396

190.15315

   

Total

95

21969.49

     

 

In order to estimate slope and intercept we conduct the linear regression.

Simple linear regression results for Group=Normotensive:
Dependent Variable: Diastolic (night)
Independent Variable: Diastolic (day) 
Diastolic (night) = 33.74505 + 0.28960396 Diastolic (day)
Sample size: 24
R (correlation coefficient) = 0.34737345
R-sq = 0.12066832
Estimate of error standard deviation: 4.3250183

Parameter estimates:

Parameter

Estimate

Std. Err.

DF

95% L. Limit

95% U. Limit

Intercept

33.74505

11.977689

22

8.9048439

58.585255

Slope

0.28960396

0.16667593

22

-0.056060763

0.63526868


Analysis of variance table for regression model:

Source

DF

SS

MS

F-stat

P-value

Model

1

56.472772

56.472772

3.0190007

0.0963

Error

22

411.52723

18.705783

   

Total

23

468

     

 

Simple linear regression results for Group=Preeclampsia:
Dependent Variable: Diastolic (night)
Independent Variable: Diastolic (day) 
Diastolic (night) = -45.181135 + 1.4091046 Diastolic (day)
Sample size: 24
R (correlation coefficient) = 0.84460369
R-sq = 0.71335539
Estimate of error standard deviation: 7.4342533

Parameter estimates:

Parameter

Estimate

Std. Err.

DF

95% L. Limit

95% U. Limit

Intercept

-45.181135

16.929738

22

-80.291262

-10.071008

Slope

1.4091046

0.19043677

22

1.0141629

1.8040463


Analysis of variance table for regression model:

Source

DF

SS

MS

F-stat

P-value

Model

1

3025.9347

3025.9347

54.750091

<0.0001

Error

22

1215.8987

55.268122

   

Total

23

4241.8333

     

 

Future Studies:

 I think that a larger sample size should be used. I also think that we should examine if they have had treatment or any medications that they are on. We should also look at their exercise levels and which activities they are participating in and how they are sleeping. Their stress levels should also be evaluated. There is a lot that could interfere and affect the BP here. 

 

 

HTML link:
<A href="https://www.statcrunch.com/5.0/viewreport.php?reportid=73943">DIastolic BP- Linear Regression </A>

Comments
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By nku.katie.waters
Nov 20, 2017

Hi Candace,
This is a good start. A few comments:
1. You state that you are going to examine the relationship between systolic blood pressure - day vs. night, but you use the diastolic in your analysis.

2. You should omit the One-Way ANOVA results as it is not appropriate here. To test for a correlation, we need to use Simple Linear Regression. (We use One-Way ANOVA to test for mean differences between 2 or more independent groups.)

3. You should check the assumptions for regression analysis. We need to check normality and constant variability. These can be checked with a "QQ Plot of Residuals" and "Residuals vs. X-values", respectively.

4. You were expected to interpret the estimates for slope. . For the preeclampsia group (comparing systolic day vs systolic night), a correct interpretation of the slope: With 95% confidence, we estimate the slope of our true regression line to be between 0.81 and 1.52. Putting this in context of the problem, we can say that a one BPM increase in daytime Systolic BP will correspond to a 0.81 to 1.52 BPM increase in the AVERAGE night-time Systolic BP for preeclampsia women. (We would interpret the slope for the normotensive group similarly.)

5. 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=120, a correct interpretation would be: For a preeclampsia individual with 120bpm daytime SBP, the estimated nighttime SBP is between 88.5 and 126.3bpm for the nighttime measurement. Remember that a PI is interpreted for an INDIVDUAL – not average.

Please review the solutions and let me know if you have any questions.

Always Learning