Longitudinal analysis pipeline with longdat_disc()

Time (the proxy for treatment) as a discrete variable

Introduction

This is an example of running longdat_disc(). Note that the time variable (proxy of treatment) here should be discrete. If the time variable is continuous, please apply longdat_cont() instead.

# Load the packages
library(LongDat)
library(tidyverse)
library(kableExtra)

Explaining the input data frame format

The input data frame (called master table) should have the same format as the example data “LongDat_disc_master_table”. If you have metadata and feature (eg. microbiome, immunome) data stored in separate tables, you can go to the section Preparing the input data frame with make_master_table() below. The function make_master_table() helps you to create master table from metadata and feature tables.

Now let’s have a look at the required format for the input master table. The example below is a dummy longitudinal data set with 3 time points (1, 2, 3). Here we want to see if the treatment has a significant effect on gut microbial abundance or not.

# Read in the data frame. LongDat_disc_master_table is already lazily loaded.
master <- LongDat_disc_master_table
master %>%
    kableExtra::kbl() %>%
    kableExtra::kable_paper(bootstrap_options = "responsive", font_size = 12) %>%
    kableExtra::scroll_box(width = "700px", height = "200px")
Individual Time_point sex age DrugA DrugB BacteriumA BacteriumB BacteriumC
1 1 0 61 0.0 10 11 4 23
1 2 0 61 0.0 10 13 2 44
1 3 0 61 0.0 20 7 13 48
2 1 0 66 0.0 640 344 0 48
2 2 0 66 0.0 320 3 0 80
2 3 0 66 0.0 640 379 0 87
3 1 0 63 7.5 100 55 0 95
3 2 0 63 7.5 0 5 0 160
3 3 0 63 7.5 100 205 0 210
4 1 0 47 0.0 300 60 0 126
4 2 0 47 0.0 200 4 0 130
4 3 0 47 0.0 300 64 59 186
5 1 1 51 0.0 160 100 20 15
5 2 1 51 0.0 130 3 64 8
5 3 1 51 0.0 160 53 5 34
6 1 1 53 10.0 0 32 138 0
6 2 1 53 10.0 0 2 0 5
6 3 1 53 10.0 0 10 0 2
7 1 0 50 0.0 40 22 105 69
7 2 0 50 0.0 20 27 158 40
7 3 0 50 0.0 40 32 100 113
8 1 1 54 0.0 100 24 0 0
8 2 1 54 0.0 80 0 0 0
8 3 1 54 0.0 160 192 0 2
9 1 0 44 0.0 160 65 0 1
9 2 0 44 0.0 80 1 0 31
9 3 0 44 0.0 160 12 0 31
10 1 0 60 0.0 100 19 163 163
10 2 0 60 0.0 25 0 41 155
10 3 0 60 0.0 100 43 13 180

As you can see, the “Individual” is at the first column, and the features (dependent variables), which are gut microbial abundances in this case, are at the end of the table. Any column apart from individual, test_var (e.g. Time_point) and dependent variables will be taken as potential covariates (could be confounder or mediator). For example, here the potential covariates are sex, age, drug A and drug B. Please avoid using characters that don’t belong to ASCII printable characters for the column names in the input data frame.

Preparing the input data frame with make_master_table()

If you have your input master table prepared already, you can skip this section and go to Run longdat_disc() directly. If your metadata and feature (eg. microbiome, immunome) data are stored in two tables, you can create a master table out of them easily with the function make_master_table().

First, let’s take a look at an example of the metadata table. Metadata table should be a data frame whose columns consist of sample identifiers (sample_ID, unique for each sample), individual, time point and other meta data. Each row corresponds to one sample_ID.

# Read in the data frame. LongDat_disc_metadata_table is already lazily loaded.
metadata <- LongDat_disc_metadata_table
metadata %>%
    kableExtra::kbl() %>%
    kableExtra::kable_paper(bootstrap_options = "responsive", font_size = 12) %>%
    kableExtra::scroll_box(width = "700px", height = "200px")
Sample_ID Individual Time_point sex age DrugA DrugB
1_1 1 1 0 61 0.0 10
1_2 1 2 0 61 0.0 10
1_3 1 3 0 61 0.0 20
2_1 2 1 0 66 0.0 640
2_2 2 2 0 66 0.0 320
2_3 2 3 0 66 0.0 640
3_1 3 1 0 63 7.5 100
3_2 3 2 0 63 7.5 0
3_3 3 3 0 63 7.5 100
4_1 4 1 0 47 0.0 300
4_2 4 2 0 47 0.0 200
4_3 4 3 0 47 0.0 300
5_1 5 1 1 51 0.0 160
5_2 5 2 1 51 0.0 130
5_3 5 3 1 51 0.0 160
6_1 6 1 1 53 10.0 0
6_2 6 2 1 53 10.0 0
6_3 6 3 1 53 10.0 0
7_1 7 1 0 50 0.0 40
7_2 7 2 0 50 0.0 20
7_3 7 3 0 50 0.0 40
8_1 8 1 1 54 0.0 100
8_2 8 2 1 54 0.0 80
8_3 8 3 1 54 0.0 160
9_1 9 1 0 44 0.0 160
9_2 9 2 0 44 0.0 80
9_3 9 3 0 44 0.0 160
10_1 10 1 0 60 0.0 100
10_2 10 2 0 60 0.0 25
10_3 10 3 0 60 0.0 100

This example is a dummy longitudinal meatadata with 3 time points for each individual. Besides sample_ID, individual, time point columns, there are also information of sex, age and drugs that individuals take. Here we want to see if the treatment has a significant effect on gut microbial abundance or not.

Then, let’s see how a feature table looks like. Feature table should be a data frame whose columns only consist of sample identifiers (sample_ID) and features (dependent variables, e.g. microbiome). Each row corresponds to one sample_ID. Please do not include any columns other than sample_ID and features in the feature table.

# Read in the data frame. LongDat_disc_feature_table is already lazily loaded.
feature <- LongDat_disc_feature_table
feature %>%
    kableExtra::kbl() %>%
    kableExtra::kable_paper(bootstrap_options = "responsive", font_size = 12) %>%
    kableExtra::scroll_box(width = "700px", height = "200px")
Sample_ID BacteriumA BacteriumB BacteriumC
1_1 11 4 23
1_2 13 2 44
1_3 7 13 48
2_1 344 0 48
2_2 3 0 80
2_3 379 0 87
3_1 55 0 95
3_2 5 0 160
3_3 205 0 210
4_1 60 0 126
4_2 4 0 130
4_3 64 59 186
5_1 100 20 15
5_2 3 64 8
5_3 53 5 34
6_1 32 138 0
6_2 2 0 5
6_3 10 0 2
7_1 22 105 69
7_2 27 158 40
7_3 32 100 113
8_1 24 0 0
8_2 0 0 0
8_3 192 0 2
9_1 65 0 1
9_2 1 0 31
9_3 12 0 31
10_1 19 163 163
10_2 0 41 155
10_3 43 13 180

This example is a dummy longitudinal feature data. It stores the gut microbial abundance of each sample.

To enable the joining process of metadata and feature tables, please pay attention to the following rules.

  1. The row numbers of metadata and feature tables should be the same.
  2. Sample_IDs are unique for each sample (i.e. no repeated sample_ID)
  3. Metadata and feature tables have the same sample_IDs. If sample_IDs don’t match between the two tables, the joining process will fail.
  4. As mentioned above, feature table should include only the columns of sample_ID and features.
  5. Avoid using characters that don’t belong to ASCII printable characters for the column names.

Now let’s create a master table and take a look at the result!

master_created <- make_master_table(metadata_table = LongDat_disc_metadata_table,
    feature_table = LongDat_disc_feature_table, sample_ID = "Sample_ID", individual = "Individual")
#> [1] "Finished creating master table successfully!"

master_created %>%
    kableExtra::kbl() %>%
    kableExtra::kable_paper(bootstrap_options = "responsive", font_size = 12) %>%
    kableExtra::scroll_box(width = "700px", height = "200px")
Individual Time_point sex age DrugA DrugB BacteriumA BacteriumB BacteriumC
1 1 0 61 0.0 10 11 4 23
1 2 0 61 0.0 10 13 2 44
1 3 0 61 0.0 20 7 13 48
2 1 0 66 0.0 640 344 0 48
2 2 0 66 0.0 320 3 0 80
2 3 0 66 0.0 640 379 0 87
3 1 0 63 7.5 100 55 0 95
3 2 0 63 7.5 0 5 0 160
3 3 0 63 7.5 100 205 0 210
4 1 0 47 0.0 300 60 0 126
4 2 0 47 0.0 200 4 0 130
4 3 0 47 0.0 300 64 59 186
5 1 1 51 0.0 160 100 20 15
5 2 1 51 0.0 130 3 64 8
5 3 1 51 0.0 160 53 5 34
6 1 1 53 10.0 0 32 138 0
6 2 1 53 10.0 0 2 0 5
6 3 1 53 10.0 0 10 0 2
7 1 0 50 0.0 40 22 105 69
7 2 0 50 0.0 20 27 158 40
7 3 0 50 0.0 40 32 100 113
8 1 1 54 0.0 100 24 0 0
8 2 1 54 0.0 80 0 0 0
8 3 1 54 0.0 160 192 0 2
9 1 0 44 0.0 160 65 0 1
9 2 0 44 0.0 80 1 0 31
9 3 0 44 0.0 160 12 0 31
10 1 0 60 0.0 100 19 163 163
10 2 0 60 0.0 25 0 41 155
10 3 0 60 0.0 100 43 13 180

The table “master_created” is just the same as the table “master” or “LongDat_disc_master_table” in the previous section, with the “Individual” as the first column, and the features (dependent variables), which are gut microbial abundances in this case, are at the end of the table. Any column apart from individual, test_var (e.g. Time_point) and dependent variables will be taken as potential covariates (could be confounder or mediator). For the details of the arguments, please read the help page of this function by using ?make_master_table.

OK, now we’re ready to run longdat_disc()!

Run longdat_disc()

The input is the example data frame LongDat_disc_master_table (same as “master” or “master_created” in the previous sections), and the data_type is “count” since the dependent variables (features, in this case they’re gut microbial abundance) are count data. The “test_var” is the independent variable you’re testing, and here we’re testing “Time_point” (time as the proxy for treatment). The variable_col is 7 because the dependent variables start at column 7. And the fac_var mark the columns that aren’t numerical. For the details of the arguments, please read the help page of this function by using ?longdat_disc.

The run below takes less than a minute to complete. When data_type equals to “count”, please remember to set seed (as shown below) so that you’ll get reproducible randomized control test.

# Run longdat_disc() on LongDat_disc_master_table
set.seed(100)
test_disc <- longdat_disc(input = LongDat_disc_master_table, data_type = "count",
    test_var = "Time_point", variable_col = 7, fac_var = c(1:3))
#> [1] "Start data preprocessing."
#> [1] "Finish data preprocessing."
#> [1] "Start selecting potential covariates."
#> [1] 1
#> [1] 2
#> [1] 3
#> [1] 1
#> [1] 2
#> [1] 3
#> [1] "Finished selecting potential covariates."
#> [1] "Start null model test and post-hoc test."
#> [1] 1
#> [1] 2
#> [1] 3
#> [1] "Finish null model test and post-hoc test."
#> [1] "Start covariate model test."
#> [1] 1
#> [1] 2
#> [1] 3
#> [1] "Finish covariate model test."
#> [1] "Start unlisting tables from covariate model result."
#> [1] "Finish unlisting tables from covariate model result."
#> [1] "Start calculating effect size."
#> [1] 1
#> [1] 2
#> [1] 3
#> [1] "Finish calculating effect size."
#> [1] "Start randomized negative control model test."
#> [1] 1
#> [1] 2
#> [1] 3
#> [1] 1
#> [1] 2
#> [1] 3
#> [1] "Finish randomized negative control model test."
#> [1] "Start Wilcoxon post-hoc test."
#> [1] "Finish Wilcoxon post-hoc test."
#> [1] "Start removing the dependent variables to be exlcuded."
#> [1] "Finish removing the dependent variables to be exlcuded."
#> [1] "Start multiple test correction on null model test p values."
#> [1] "Finish multiple test correction on null model test p values."
#> [1] "Start generating result tables."
#> [1] "Not_reducible_to_covariate"
#> [1] "Finished successfully!"

If you have completed running the function successfully, you’ll see the message “Finished successfully!” at the end. The results are stored in list format.

Results

The major output from longdat_disc() include a result table and a covariate table. If you have count data (data_type equals to “count”), then there are chances that you get a third table “randomized control table”. For more details about the “randomized control table”, please read the help page of this function by using ?longdat_disc.

Result table

Let’s have a look at the result table first.

# The first dataframe in the list is the result table
result_table <- test_disc[[1]]
result_table %>%
    kableExtra::kbl() %>%
    kableExtra::kable_paper(bootstrap_options = "responsive", font_size = 12, position = "center") %>%
    kableExtra::scroll_box(width = "700px")
Feature Prevalence_percentage Mean_abundance Signal Effect_1_2 Effect_1_3 Effect_2_3 EffectSize_1_2 EffectSize_1_3 EffectSize_2_3 Null_time_model_q Post-hoc_q_1_2 Post-hoc_q_1_3 Post-hoc_q_2_3
BacteriumA 93.333 59.567 OK_nrc Decreased NS Enriched -0.6 0.2 0.8 0.0000001 0.0000732 0.5131158 0.0000360
BacteriumB 46.667 29.500 NS NS NS NS -0.1 -0.2 -0.1 0.7869569 0.8016484 0.8016484 0.8016484
BacteriumC 90.000 69.533 OK_nc NS Enriched NS 0.3 1.0 0.7 0.0018420 0.0806579 0.0035489 0.0806579

The second and third columns show the prevalence and mean abundance of each feature According to the “Signal” column, treatment is a significant predictor for BacteriumA as it shows “OK_nrc” (which represents “OK and not reducible to covariate”), meaning that there are potential covariates, however there is an effect of time (proxy of treatment) and it is independent of those of covariates. To find out what the covariates are, you’ll need to see the covariate table, but we’ll get to that later. On the other hand, the signal for BacteriumC is “OK_nc” (which represents OK and no covariate), meaning that the abundance of BacteriumC alters significantly throughout time (proxy of treatment), and that there is no potential covariate. As for BacteriumB, time (proxy of treatment) has no effect on its abundance.

The following columns “Effect_1_2”, “Effect_1_3” and “Effect_2_3” describe how features (dependent variables) change from time point a to b. Here we can tell that BacteriumA decreases from time point 1 to 2, and then enriched from time point 2 to 3. From the columns “EffectSize_1_2” and “EffectSize_2_3”, we know that the effect size are -0.6 and 0.8. The most relevant information for users ends here, which are listed from the first column to “EffectSize” columns.

Then the following columns contain the details of model test p values (“Null_time_model_q”), the post-hoc test p values (Post.hoc_q_1_2, Post.hoc_q_1_3 and Post.hoc_q_2_3). For more detailed information of the columns in the result table, please refer to the help page by using ?longdat_disc.

The explanation of each type of “Signal” is listed below.

Signal Meaning Explanation
NS Non-significant There’s no effect of time.
OK_nc OK and no covariate There’s an effect of time and there’s no potential covariate.
OK_d OK but doubtful There’s an effect of time and there’s no potential covariate, however the confidence interval of the test_var estimate in the model test includes zero, and thus it is doubtful. Please check the raw data (e.g., plot feature against time) to confirm if there is real effect of time.
OK_nrc OK and not reducible to covariate There are potential covariates, however there’s an effect of time and it is independent of those of covariates.
EC Entangled with covariate There are potential covariates, and it isn’t possible to conclude whether the effect is resulted from time or covariates.
RC Effect reducible to covariate There’s an effect of time, but it can be reduced to the covariate effects.

Covariate table

Next, let’s take a look at the covariate table.

# The second dataframe in the list is the covariate table
covariate_table <- test_disc[[2]]
covariate_table %>%
    kableExtra::kbl() %>%
    kableExtra::kable_paper(bootstrap_options = "responsive", font_size = 12, position = "center") %>%
    kableExtra::scroll_box(width = "700px")
Feature Covariate1 Covariate_type1 Effect_size1 Covariate2 Covariate_type2 Effect_size2
BacteriumA DrugB Not_reducible_to_covariate 0.4943542 NA NA NA

The columns of this covariate table are grouped every three columns. “Covariate1” is the name of the covariate, while “Covariate_type1” is the covariate type of covariate1, that is, if the effect of time is reducible to covariate1. “Effect_size1” is the effect size of the dependent variable values between different levels of covariate1. Here, the effect of time isn’t reducible to covariate1, so we don’t need to worry about the covariate effect of covariate1 on bacteriumA. If there are more than one covariates, they will be listed along the rows of each dependent variable.

Result interpretation

From the result above, we see that the potential covariate for BacteriumA is DrugB, but we don’t need to worry about the effect of time (proxy for the treatment) being able to reduce to DrugB since it’s covariate type is “not reducible to covariate”, meaning that the effect of time is independent from the effect of DrugB. With this information, we confirm that the treatment can solely explain the changes in BacteriumA abundance. All together, the treatment induces significant changes on the abundance of BacteriumA and BacteriumC, while causing no alteration in that of BacteriumB.

Plotting the result

Finally, we can plot the result with the function cuneiform_plot(). The required input is a result table from longdat_disc() (or any table with the same format as a result table does).

test_plot <- cuneiform_plot(result_table = test_disc[[1]], x_axis_order = c("Effect_1_2",
    "Effect_2_3", "Effect_1_3"), title_size = 15)
#> [1] "Finished plotting successfully!"
test_plot

Here we can see the result clearly from the cuneiform plot. It shows the features whose signals are not “NS”. The left panel displays the effects in each time interval. Red represents positive effect size while blue describes negative one (colors can be customized by users). Signficant signals are indicated by solid shapes, whereas insignificant signals are denoted by transparent ones. The right panel displays the covariate status of each feature, and users can remove it by specifying covariate_panel = FALSE. For more details of the arguments, please read the help page of this function by using ?cuneiform_plot.

Wrap-up

This tutorial ends here! If you have any further questions and can’t find the answers in the vignettes or help pages, please contact the author ().