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updates chapter 4

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Kyle Belanger 2023-06-07 13:33:09 -04:00
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61
ML/2-modeling.R
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@ -54,6 +54,8 @@ strata_table <- strata1 %>%
dplyr::left_join(strata2) %>%
dplyr::rename(Class = name)
save(list = c("strata_table"), file = "figures/strata_table.Rda")
# random forest classification -----------------------------------------------------------
@ -121,13 +123,68 @@ class_test_result_conf_matrix <- ys$conf_mat(
class_test_results %>% tune::collect_predictions()
,truth = ft4_dia
,estimate = .pred_class
)
) %>% autoplot(type = "heatmap")
gp2$ggsave(
here("figures","conf_matrix_class.emf")
,width = 7
,height = 7
,dpi = 300
,device = devEMF::emf
)
gp2$ggsave(
here("figures","conf_matrix_class.png")
,width = 7
,height = 7
,dpi = 300
)
ys$accuracy(class_test_results %>% tune::collect_predictions() ,truth = ft4_dia, estimate = .pred_class )
class_test_results %>%
workflows::extract_fit_parsnip() %>%
vip::vip(num_features = 10)
vip::vip()
gp2$ggsave(
here("figures","vip_class.emf")
,width = 7
,height = 7
,dpi = 300
,device = devEMF::emf
)
gp2$ggsave(
here("figures","vip_class.png")
,width = 7
,height = 7
,dpi = 300
)
class_test_results %>%
workflows::extract_fit_parsnip() %>%
vip::vi() %>%
dplyr::filter(!Variable == "TSH") %>%
vip::vip()
class_result_pred_ds <- class_test_results %>% tune::collect_predictions()
ys$roc_auc(class_result_pred_ds, ft4_dia,.pred_Hypo , `.pred_Non-Hypo`, .pred_Hyper, `.pred_Non-Hyper`)
roc_curve_class <- ys$roc_curve(class_result_pred_ds, ft4_dia,.pred_Hypo , `.pred_Non-Hypo`, .pred_Hyper, `.pred_Non-Hyper`) %>%
p$autoplot()
gp2$ggsave(
here("figures","roc_curve_class.emf")
,width = 7
,height = 7
,dpi = 300
,device = devEMF::emf
)
gp2$ggsave(
here("figures","roc_curve_class.png")
,width = 7
,height = 7
,dpi = 300
)
# x-boost- class ----------------------------------------------------------

100
chapter3.qmd
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@ -2,11 +2,22 @@
## IRB
Based on the information you submitted for this project, the Campbell University Institutional Review Board (Campbell IRB) determined this submission is Not Human Subjects Research as defined by 45 CFR 46.102(e).
Based on the information you submitted for this project, the Campbell
University Institutional Review Board (Campbell IRB) determined this
submission is Not Human Subjects Research as defined by 45 CFR
46.102(e).
## Population and Data
This study used the Medical Information Mart for Intensive Care (MIMIC) database [@johnsonalistair]. MIMIC (Medical Information Mart for Intensive Care) is an extensive, freely-available database comprising de-identified health-related data from patients who were admitted to the critical care units of the Beth Israel Deaconess Medical Center. The database contains many different types of information, but only data from the patients and laboratory events table are used in this study. The study uses version IV of the database, comprising data from 2008 - 2019.
This study used the Medical Information Mart for Intensive Care (MIMIC)
database [@johnsonalistair]. MIMIC (Medical Information Mart for
Intensive Care) is an extensive, freely-available database comprising
de-identified health-related data from patients who were admitted to the
critical care units of the Beth Israel Deaconess Medical Center. The
database contains many different types of information, but only data
from the patients and laboratory events table are used in this study.
The study uses version IV of the database, comprising data from 2008 -
2019.
## Data Variables and Outcomes
@ -17,19 +28,37 @@ source(here::here("ML","1-data-exploration.R"))
```
A total of 18 variables were chosen for this study. The age and gender of the patient were pulled from the patient table in the MIMIC database. While this database contains some additional demographic information, it is incomplete and thus unusable for this study. 15 lab values were selected for this study, this includes:
A total of 18 variables were chosen for this study. The age and gender
of the patient were pulled from the patient table in the MIMIC database.
While this database contains some additional demographic information, it
is incomplete and thus unusable for this study. 15 lab values were
selected for this study, this includes:
- **BMP**: BUN, bicarbonate, calcium, chloride, creatinine, glucose, potassium, sodium
- **BMP**: BUN, bicarbonate, calcium, chloride, creatinine, glucose,
potassium, sodium
- **CBC**: Hematocrit, hemoglobin, platelet count, red blood cell count, white blood cell count
- **CBC**: Hematocrit, hemoglobin, platelet count, red blood cell
count, white blood cell count
- TSH
- Free T4
The unique patient id and chart time were also retained for identifying each sample. Each sample contains one set of 15 lab values for each patient. Patients may have several samples in the data set run at different times. Rows were retained as long as they had less than three missing results. These missing results can be filled in by imputation later in the process. Samples were also filtered for those with TSH above or below the reference range of 0.27 - 4.2 uIU/mL. These represent samples that would have reflexed for Free T4 testing. After filtering, the final data set contained `r nrow(ds1)` rows.
The unique patient id and chart time were also retained for identifying
each sample. Each sample contains one set of 15 lab values for each
patient. Patients may have several samples in the data set run at
different times. Rows were retained as long as they had less than three
missing results. These missing results can be filled in by imputation
later in the process. Samples were also filtered for those with TSH
above or below the reference range of 0.27 - 4.2 uIU/mL. These represent
samples that would have reflexed for Free T4 testing. After filtering,
the final data set contained `r nrow(ds1)` rows.
Once the final data set was collected, an additional column was created for the outcome variable to determine if the Free T4 value was diagnostic. This outcome variable was used for building classification models. The classification variable was not used in regression models. @tbl-outcome_var shows how the outcomes were added
Once the final data set was collected, an additional column was created
for the outcome variable to determine if the Free T4 value was
diagnostic. This outcome variable was used for building classification
models. The classification variable was not used in regression models.
@tbl-outcome_var shows how the outcomes were added
| TSH Value | Free T4 Value | Outcome |
|---------------|---------------|---------------------|
@ -40,7 +69,14 @@ Once the final data set was collected, an additional column was created for the
: Outcome Variable {#tbl-outcome_var}
. @tbl-data_summary shows the summary statistics of each variable selected for the study. Each numeric variable is listed with the percent missing, median, and interquartile range (IQR). The data set is weighted toward elevated TSH levels, with 80% of values falling into that category. Glucose and Calcium have several missing values at `r gtsummary::inline_text(summary_tbl, variable = GLU, column = n)` and `r gtsummary::inline_text(summary_tbl, variable = CA, column = n)`, respectively.
. @tbl-data_summary shows the summary statistics of each variable
selected for the study. Each numeric variable is listed with the percent
missing, median, and interquartile range (IQR). The data set is weighted
toward elevated TSH levels, with 80% of values falling into that
category. Glucose and Calcium have several missing values at
`r gtsummary::inline_text(summary_tbl, variable = GLU, column = n)` and
`r gtsummary::inline_text(summary_tbl, variable = CA, column = n)`,
respectively.
```{r}
#| label: tbl-data_summary
@ -52,19 +88,41 @@ summary_tbl %>% gtsummary$as_kable()
## Data Inspection
By examining @tbl-data_summary several important data set characteristics quickly come to light without explanation. The median age across the data set, as a whole, is quite similar, with a median age across all categories of 62.5. Females are better represented in the data set, with higher percentages in all categories. Across all categories, the median values for each lab result are pretty similar. The expectation for this is Red Blood cells, which show more considerable variation across the various categories.
By examining @tbl-data_summary several important data set
characteristics quickly come to light without explanation. The median
age across the data set, as a whole, is quite similar, with a median age
across all categories of 62.5. Females are better represented in the
data set, with higher percentages in all categories. Across all
categories, the median values for each lab result are pretty similar.
The expectation for this is Red Blood cells, which show more
considerable variation across the various categories.
![Distribution of Variables](figures/distrubution_histo){#fig-distro_histo}
![Distribution of
Variables](figures/distrubution_histo){#fig-distro_histo}
When examining @fig-distro_histo, many clinical chemistry values do not show a standard distribution. However, the hematology results typically do appear to follow a standard distribution. While not a problem for most tree-based classification models, many regression models perform better with standard variables. Standardizing variables provides a common comparable unit of measure across all the variables [@boehmke2020]. Since lab values do not contain negative numbers, all numeric values will be log-transformed to bring them to normal distributions.
When examining @fig-distro_histo, many clinical chemistry values do not
show a standard distribution. However, the hematology results typically
do appear to follow a standard distribution. While not a problem for
most tree-based classification models, many regression models perform
better with standard variables. Standardizing variables provides a
common comparable unit of measure across all the variables
[@boehmke2020]. Since lab values do not contain negative numbers, all
numeric values will be log-transformed to bring them to normal
distributions.
![Variable Correlation Plot](figures/corr_plot){#fig-corr_plot}
@fig-corr_plot shows a high correlation between Hemoglobin, hematocrit, and Red Blood Cell values (as expected). While high correlation does not lead to model issues, it can cause unnecessary computations with little value. However, due to the small number of variables, the computation burden is not expected to cause delays, and thus the variables will not be removed.
@fig-corr_plot shows a high correlation between Hemoglobin, hematocrit,
and Red Blood Cell values (as expected). While high correlation does not
lead to model issues, it can cause unnecessary computations with little
value. However, due to the small number of variables, the computation
burden is not expected to cause delays, and thus the variables will not
be removed.
## Data Tools
All data handling and modeling were performed using R and R Studio. The current report was rendered in the following environment.
All data handling and modeling were performed using R and R Studio. The
current report was rendered in the following environment.
```{r}
#| label: tbl-platform-info
@ -118,7 +176,14 @@ knitr::kable(
## Model Selection
Both classification and regression models were screened using a random grid search to tune hyperparameters. The models were tested against the training data set to find the best-fit model. @fig-reg-screen shows the results of the model screening for regression models, using root mean square error (RMSE) as the ranking method. Random Forest models and boosted trees performed similarly and were selected for further testing. A full grid search was performed on both models, with a Random Forest model as the final selection. The final hyperparameters selected were:
Both classification and regression models were screened using a random
grid search to tune hyperparameters. The models were tested against the
training data set to find the best-fit model. @fig-reg-screen shows the
results of the model screening for regression models, using root mean
square error (RMSE) as the ranking method. Random Forest models and
boosted trees performed similarly and were selected for further testing.
A full grid search was performed on both models, with a Random Forest
model as the final selection. The final hyperparameters selected were:
- mtry: 8
@ -128,7 +193,12 @@ Both classification and regression models were screened using a random grid sear
![Regression Model Screen](figures/reg_screen){#fig-reg-screen}
@fig-class-screen shows the results of the model screen for classification models using accuracy as the ranking method. As with regression models, boosted trees and random forest models performed the best. After completing a full grid search of both model types, a random forest model was again chosen as the final model. The final hyperparameters for the model selected were:
@fig-class-screen shows the results of the model screen for
classification models using accuracy as the ranking method. As with
regression models, boosted trees and random forest models performed the
best. After completing a full grid search of both model types, a random
forest model was again chosen as the final model. The final
hyperparameters for the model selected were:
- mtry: 8

38
chapter4.qmd
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@ -2,10 +2,9 @@
```{r}
#| include: false
#| cache: true
library(magrittr)
load("test.Rda")
load(here:here("figures", "strata_table.Rda"))
```
@ -29,7 +28,7 @@ strata_table %>% knitr::kable()
First, the report shows the ability of classification algorithms to
predict whether Free T4 will be diagnostic, with the prediction quality
measured by Area Under Curve (AUC) and accuracy. Data regarding the
univariate association between each predictor analyte and the Free T4
importance association between each predictor analyte and the Free T4
Diagnostic value is then presented. Finally, data is presented with the
extent to which FT4 can be predicted by examining the correlation
statistics denoting the relationship between measured and predicted Free
@ -42,4 +41,35 @@ numerical laboratory results is often just whether the results fall
within the normal reference range [@luo2016]. In the case of Free T4
reflex testing, the results will either fall within the normal range
indicating the Free T4 is not diagnostic of Hyper or Hypo Throydism, or
they will fall outside those ranges indicating they are diagnostic.
they will fall outside those ranges indicating they are diagnostic. The
final model achieved an accuracy of 0.796 and an AUC of 0.918.
@fig-roc_curve provides ROC curves for each of the four outcome classes.
![ROC curves for each of the four outcome
classes](figures/roc_curve_class){#fig-roc_curve}
@fig-conf-matrix-class shows the confusion matrix of the final testing
data. Of the 2269 total results, 1805 were predicted correctly, leaving
464 incorrectly predicted results. Of the incorrectly predicted results,
72 results predicted a diagnostic Free T4 when the correct result was
non-diagnostic. 392 of the incorrectly predicted results were predicted
as non-diagnostic when the correct result was diagnostic.
![Final Model Confusion
Matrix](figures/conf_matrix_class){#fig-conf-matrix-class}
## Contributions of Individual Analytes
Understanding how an ML model makes predictions helps build trust in the
model and is the fundamental idea of the emerging field of interpretable
machine learning (IML) [@greenwell2020]. @fig-vip-class shows the
importance of features in the final model. Importance can be defined as
the extent to which a feature has a \"meaningful\" impact on the
predicted outcome [@laan2006]. As expected, TSH is the leading variable
in importance rankings, leading all other variables by over 2000's
points. The following three variables are all parts of a Complete Blood
Count (CBC), followed by the patients glucose value.
![Variable Importance Plot](figures/vip_class){#fig-vip-class}
## Predictability of Free T4 Results (Regression)

29
references.bib
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@ -350,3 +350,32 @@ DOI: 10.13026/S6N6-XD98}
note = {PMID: 27329638},
langid = {eng}
}
@article{greenwell2020,
title = {Variable Importance Plots{\textemdash}An Introduction to the vip Package},
author = {Greenwell, {Brandon,M.} and Boehmke, {Bradley,C.}},
year = {2020},
date = {2020},
journal = {The R Journal},
pages = {343},
volume = {12},
number = {1},
doi = {10.32614/RJ-2020-013},
url = {https://journal.r-project.org/archive/2020/RJ-2020-013/index.html},
langid = {en}
}
@article{laan2006,
title = {Statistical Inference for Variable Importance},
author = {Laan, Mark J. van der},
year = {2006},
month = {02},
date = {2006-02-20},
journal = {The International Journal of Biostatistics},
volume = {2},
number = {1},
doi = {10.2202/1557-4679.1008},
url = {https://www.degruyter.com/document/doi/10.2202/1557-4679.1008/html},
note = {Publisher: De Gruyter},
langid = {en}
}