# Interpret ColocBoost Output

This vignette demonstrates how to interpret the output of ColocBoost, specifically to get the summary of colocalization and focusing only on strong colocalization events.

    library(colocboost)

## 1. Summarize ColocBoost results

### Causal variant structure

The dataset features two causal variants with indices 194 and 589.

- Causal variant 194 is associated with traits 1, 2, 3, and 4.
- Causal variant 589 is associated with traits 2, 3, and 5.

    # Loading the Dataset
    data(Ind_5traits)
    # Run colocboost
    res <- colocboost(X = Ind_5traits$X, Y = Ind_5traits$Y)
    #> Validating input data.
    #> Starting gradient boosting algorithm.
    #> Gradient boosting for outcome 4 converged after 40 iterations!
    #> Gradient boosting for outcome 5 converged after 59 iterations!
    #> Gradient boosting for outcome 1 converged after 61 iterations!
    #> Gradient boosting for outcome 3 converged after 91 iterations!
    #> Gradient boosting for outcome 2 converged after 94 iterations!
    #> Performing inference on colocalization events.
    cos_summary <- res$cos_summary
    names(cos_summary)
    #>  [1] "focal_outcome"             "colocalized_outcomes"
    #>  [3] "cos_id"                    "purity"
    #>  [5] "top_variable"              "top_variable_vcp"
    #>  [7] "cos_npc"                   "min_npc_outcome"
    #>  [9] "n_variables"               "colocalized_index"
    #> [11] "colocalized_variables"     "colocalized_variables_vcp"

The `cos_summary` object contains the colocalization summary for all colocalization events, with each row representing a single colocalization event. The summary includes the following columns:

- focal_outcome: The focal outcome being analyzed, or `FALSE` if no focal outcome exists.
- colocalized_outcomes: Traits that are colocalized within the 95% colocalization confidence set (CoS).
- cos_id: A unique identifier for each 95% colocalization confidence set (CoS).
- purity: The minimum absolute correlation of variants within the 95% colocalization confidence set (CoS).
- top_variable: The variable with the highest variant colocalization probability (VCP).
- top_variable_vcp: The variant colocalization probability for the top variable.
- cos_npc: The normalized probability of colocalization for the 95% confidence set, providing empirical evidence in favor of colocalization over a trait-specific configuration.
- min_npc_outcome: The minimum normalized probability among colocalized traits.
- n_variables: The number of variables in the 95% colocalization confidence set (CoS).
- colocalized_index: The indices of colocalized variables.
- colocalized_variables: A list of colocalized variables.
- colocalized_variables_vcp: The variant colocalization probabilities for all colocalized variables.

To obtain the summary of colocalization with a specific focus on traits of interest, you can use the `get_cos_summary`, see the detailed usage of this function in link. This function allows you to filter the colocalization summary based on a particular outcome of interest, making it easier to interpret the results for specific traits. For example, if you are interested in the colocalization events involving the traits `Y1` and `Y2`, you can use the following code:

    # Get summary table of colocalization
    cos_interest_outcome <- get_cos_summary(res, interest_outcome = c("Y1", "Y2"))

## 2. Filter colocalization events by relative strength of evidence

In `cos_summary`, for each 95% CoS, the `cos_npc` column provides a normalized probability of colocalization and `min_npc_outcome` column provides the minimum normalized probability among colocalized traits. Those two metrics are measured as an empirical evidence of colocalization both in CoS-level and in trait-level. To obtain the best minimal colocalization configuration can be defined by using both `cos_npc` and `npc_outcome`. See the detailed usage of this function in link.

    filter_res <- get_robust_colocalization(res, cos_npc_cutoff = 0.5, npc_outcome_cutoff = 0.2)
    #> Extracting colocalization results with cos_npc_cutoff = 0.5 and npc_outcome_cutoff = 0.2.
    #> Keep only CoS with cos_npc >= 0.5. For each CoS, keep the outcomes configurations that the npc_outcome >= 0.2.

- The output from `get_robust_colocalization` is the same as output from `colocboost`, which can be directly used in any post inference and visualization.
- `npc=0.5` or `npc_outcome = 0.2` maintains robust colocalization signals for cases when many traits are evaluated. Higher thresholds can be specified if users want to focus only on strong colocalization events.

## 3. More details on ColocBoost output

The entire colocalization output from `colocboost` is stored in the `colocboost` object, which contains several components:

- `cos_summary`: A summary table for colocalization events (see details in above Section 1).
- `vcp`: The variable colocalized probability for each variable.
- `cos_details`: A object with all information for colocalization results.
- `data_info`: A object with the detailed information from input data.
- `model_info`: A object with the detailed information for colocboost model.

In this section, we will provide a detailed explanation of the components for deepening into ColocBoost result using a mixed dataset.

    # Load example data
    data(Ind_5traits)
    data(Sumstat_5traits)
    # Create a mixed dataset
    X <- Ind_5traits$X[1:4]
    Y <- Ind_5traits$Y[1:4]
    sumstat <- Sumstat_5traits$sumstat[5]
    LD <- get_cormat(Ind_5traits$X[[1]])
    # Run colocboost
    res <- colocboost(X = X, Y = Y, sumstat = sumstat, LD = LD)
    #> Validating input data.
    #> Starting gradient boosting algorithm.
    #> Gradient boosting for outcome 4 converged after 40 iterations!
    #> Gradient boosting for outcome 5 converged after 59 iterations!
    #> Gradient boosting for outcome 1 converged after 61 iterations!
    #> Gradient boosting for outcome 3 converged after 91 iterations!
    #> Gradient boosting for outcome 2 converged after 94 iterations!
    #> Performing inference on colocalization events.

### 3.1. Variant colocalization probability (`vcp`)

- `vcp` is the probability of a variant being colocalized with at least one traits, serving as analogs of posterior inclusion probabilities (PIPs) in single-trait fine-mapping. To plot the VCP for the variants within at least one CoS, you can use the `colocboost_plot` function with the `y` argument set to `"vcp"`.

    colocboost_plot(res, y = "vcp")

Please visit our documentation portal at Visualization of ColocBoost Results for more details on the `colocboost_plot` function

### 3.2. Analyzed data information (`data_info`)

- `n_variables`: number of variants being included.
- `variables`: vector of variant names across all traits being included in colocalization analysis.
- `coef`: regression coefficients estimated from the colocboost model for each trait.
- `z`: z-scores from marginal associations for each trait.
- `n_outcomes`: the number of traits being included in colocalization analysis.
- `outcome_info` contains information of analyzed data, including sample size and data type.

    res$data_info$outcome_info
    #>    outcome_names sample_size is_sumstats is_focal
    #> y1            Y1        1153       FALSE    FALSE
    #> y2            Y2        1153       FALSE    FALSE
    #> y3            Y3        1153       FALSE    FALSE
    #> y4            Y4        1153       FALSE    FALSE
    #> y5            Y5        1153        TRUE    FALSE

### 3.3. Colocalization details (`cos_details`)

`cos_details` provides a detailed information for colocalization events identified by `colocboost`. This section will provide a detailed explanation of the components in `cos_details`.

    names(res$cos_details)
    #> [1] "cos"                 "cos_outcomes"        "cos_vcp"
    #> [4] "cos_outcomes_npc"    "cos_npc"             "cos_min_npc_outcome"
    #> [7] "cos_purity"          "cos_top_variables"   "cos_weights"

#### 3.3.1. Colocalized variants for each CoS (`cos`)

- `cos`: A list with a detailed information of colocalized variants for each CoS.
  - `cos_index`: Indices of colocalized variables with unique identifier for each CoS.
  - `cos_variables`: Names of colocalized variables with unique identifier for each CoS.
- Note that variants are ordered by their VCP in descending order.

    res$cos_details$cos
    #> $cos_index
    #> $cos_index$`cos1:y1_y2_y3_y4`
    #> [1] 186 194 168 205
    #>
    #> $cos_index$`cos2:y2_y3_y5`
    #> [1] 589 593
    #>
    #>
    #> $cos_variables
    #> $cos_variables$`cos1:y1_y2_y3_y4`
    #> [1] "rs_186" "rs_194" "rs_168" "rs_205"
    #>
    #> $cos_variables$`cos2:y2_y3_y5`
    #> [1] "rs_589" "rs_593"

#### 3.3.2. Colocalized traits for each 95% CoS (`cos_outcomes`)

- `cos_outcomes`: A list with a detailed information of colocalized traits for each CoS.
  - `outcome_index`: Indices of colocalized traits with unique identifier for each CoS.
  - `outcome_name`: Names of colocalized traits with unique identifier for each CoS.

    res$cos_details$cos_outcomes
    #> $outcome_index
    #> $outcome_index$`cos1:y1_y2_y3_y4`
    #> [1] 1 2 3 4
    #>
    #> $outcome_index$`cos2:y2_y3_y5`
    #> [1] 2 3 5
    #>
    #>
    #> $outcome_name
    #> $outcome_name$`cos1:y1_y2_y3_y4`
    #> [1] "Y1" "Y2" "Y3" "Y4"
    #>
    #> $outcome_name$`cos2:y2_y3_y5`
    #> [1] "Y2" "Y3" "Y5"

- `cos_npc`: normalized probability of colocalization for CoS, providing empirical evidence in favor of colocalization over a trait-specific configuration.
- `cos_outcomes_npc`: normalized probability for each colocalized trait in order with evidence strength.
- These two metrics could be used to filter the colocalization events by relative strength of evidence, see details in Section 2.

    res$cos_details$cos_npc
    #> cos1:y1_y2_y3_y4    cos2:y2_y3_y5
    #>        0.9989418        0.9974159
    res$cos_details$cos_outcomes_npc
    #> $`cos1:y1_y2_y3_y4`
    #>    outcomes_index relative_logLR npc_outcome
    #> Y3              3      2.2563485   0.9890312
    #> Y1              1      1.8287003   0.9742005
    #> Y4              4      0.9499365   0.8504124
    #> Y2              2      0.6414479   0.7227667
    #>
    #> $`cos2:y2_y3_y5`
    #>    outcomes_index relative_logLR npc_outcome
    #> Y5              5       1.994252   0.9814726
    #> Y3              3       1.494458   0.9496581
    #> Y2              2       1.475390   0.9477011

- `cos_purity`: includes three lists, for each list, it contains \(S \times S\) matrix, where \(S\) is the number of CoS.
  - `min_abs_cor`: the minimum absolute correlation of variants within (diagonal) CoS or in-between (off-diagonal) different CoS.
  - `median_abs_cor`: the median absolute correlation of variants within (diagonal) CoS or in-between (off-diagonal) different CoS.
  - `max_abs_cor`: the maximum absolute correlation of variants within (diagonal) CoS or in-between (off-diagonal) different CoS.

    res$cos_details$cos_purity
    #> $min_abs_cor
    #>                  cos1:y1_y2_y3_y4 cos2:y2_y3_y5
    #> cos1:y1_y2_y3_y4     9.941612e-01  4.086608e-05
    #> cos2:y2_y3_y5        4.086608e-05  9.761542e-01
    #>
    #> $max_abs_cor
    #>                  cos1:y1_y2_y3_y4 cos2:y2_y3_y5
    #> cos1:y1_y2_y3_y4      0.996765520   0.002824775
    #> cos2:y2_y3_y5         0.002824775   0.976154165
    #>
    #> $median_abs_cor
    #>                  cos1:y1_y2_y3_y4 cos2:y2_y3_y5
    #> cos1:y1_y2_y3_y4     0.9970944352  0.0004030735
    #> cos2:y2_y3_y5        0.0004030735  0.9761541652

- `cos_top_variables`: indices and names of the top variant for each CoS, which is the variant with the highest VCP.
- Note that there may exist multiple variants in perfect LD with the same highest VCP.

    res$cos_details$cos_top_variables
    #>                  top_index top_variables
    #> cos1:y1_y2_y3_y4       186        rs_186
    #> cos2:y2_y3_y5          589        rs_589

- `cos_weights`: the integrative weights for each colocalized trait in the CoS. This is used to recalibrate CoS when some traits are filtered out..
- `cos_vcp`: the single-effect VCP for each CoS.

### 3.4. Model information (`model_info`)

- `model_coveraged`: if the model is converged.
- `outcome_model_coveraged`: if the trait-specific model is converged.
- `n_updates`: number of boosting rounds
- `outcome_n_updates`: number of boosting rounds for each trait.
- `jk_update`: indices of the variants being updated in the model at each boosting round.

    # Pick arbitrary SEC updates, see entire update in advance
    res$model_info$jk_star[c(5:10,36:38), ]
    #>             Y1  Y2  Y3  Y4  Y5
    #> jk_star_5   NA  NA  NA  NA 593
    #> jk_star_6   NA  NA  NA  NA 593
    #> jk_star_7  186 186 186 186  NA
    #> jk_star_8   NA  NA  NA  NA 593
    #> jk_star_9  186 186 186 186  NA
    #> jk_star_10  NA  NA  NA  NA 593
    #> jk_star_36 186  NA 186 186  NA
    #> jk_star_37  NA  NA 589 340  NA
    #> jk_star_38  NA  NA  NA 436  NA

- `profile_loglik`: joint profile log-likelihood changes over boosting rounds.
- `outcome_profile_loglik`: trait-specific profile log-likelihood changes over boosting rounds.

    # Plotting joint profile log-likelihood (blue) and trait-specific profile log-likelihood (red).
    par(mfrow=c(2,3),mar=c(4,4,2,1))
    plot(res$model_info$profile_loglik, type="p", col="#3366CC", lwd=2, xlab="", ylab="Joint Profile")
    for(i in 1:5){
    plot(res$model_info$outcome_profile_loglik[[i]], type="p", col="#CC3333", lwd=2, xlab="", ylab=paste0("Profile (Trait ", i, ")"))
    }

- `outcome_proximity_obj`: trait-specific proximity smoothed objective for each trait.
- `outcome_coupled_best_update_obj`: objective at the (coupled) best update variant for each outcome.

    # Save to restore default options
    oldpar <- par(no.readonly = TRUE)
    # Plotting trait-specific proximity objective
    par(mfrow=c(2,3), mar=c(4,4,2,1))
    for(i in 1:5){
    plot(res$model_info$outcome_proximity_obj[[i]], type="p", col="#3366CC", lwd=2, xlab="", ylab="Trait-specific Objective", main = paste0("Trait ", i))
    }
    par(oldpar)

    # Save to restore default options
    oldpar <- par(no.readonly = TRUE)
    # Plotting trait-specific objective at the best update variant
    par(mfrow=c(2,3), mar=c(4,4,2,1))
    for(i in 1:5){
      plot(res$model_info$outcome_coupled_best_update_obj[[i]], type="p", col="#CC3333", lwd=2, xlab="", ylab=paste0("Objective at best update variant"), main = paste0("Trait ", i))
    }
    par(oldpar)

### 3.5. Trait-specific effects information (`ucos_details`)

There is `ucos_details` in ColocBoost output when setting `output_level = 2`, including the trait-specific (uncolocalized) information from the single-effect learner (SEL).

    # Create a mixed dataset
    data(Ind_5traits)
    data(Heterogeneous_Effect)
    X <- Ind_5traits$X[1:3]
    Y <- Ind_5traits$Y[1:3]
    X1 <- Heterogeneous_Effect$X
    Y1 <- Heterogeneous_Effect$Y[,1,drop=F]
    res <- colocboost(X = c(X, list(X1)), Y = c(Y, list(Y1)), output_level = 2)
    #> Validating input data.
    #> Starting gradient boosting algorithm.
    #> Gradient boosting for outcome 1 converged after 86 iterations!
    #> Gradient boosting for outcome 3 converged after 99 iterations!
    #> Gradient boosting for outcome 4 converged after 103 iterations!
    #> Gradient boosting for outcome 2 converged after 113 iterations!
    #> Performing inference on colocalization events.
    names(res$ucos_details)
    #> [1] "ucos"                "ucos_outcomes"       "ucos_weight"
    #> [4] "ucos_top_variables"  "ucos_purity"         "cos_ucos_purity"
    #> [7] "ucos_outcomes_delta"

#### 3.5.1. Trait-specific (uncolocalized) confidence sets (`ucos`)

- `ucos`: A list containing a detailed information about trait-specific (uncolocalized) variants for each uCoS.
  - `ucos_index`: Indices of trait-specific (uncolocalized) variants.
  - `ucos_variables`: Names of trait-specific (uncolocalized) variants.

    res$ucos_details$ucos
    #> $ucos_index
    #> $ucos_index$`ucos1:y4`
    #> [1] 322
    #>
    #> $ucos_index$`ucos2:y4`
    #>  [1]  982  993  983  981  970  988  942  972 1000  987 1005  971  973  990  991
    #> [16]  958  976  977  975  906  938
    #>
    #>
    #> $ucos_variables
    #> $ucos_variables$`ucos1:y4`
    #> [1] "rs_322"
    #>
    #> $ucos_variables$`ucos2:y4`
    #>  [1] "rs_982"  "rs_993"  "rs_983"  "rs_981"  "rs_970"  "rs_988"  "rs_942"
    #>  [8] "rs_972"  "rs_1000" "rs_987"  "rs_1005" "rs_971"  "rs_973"  "rs_990"
    #> [15] "rs_991"  "rs_958"  "rs_976"  "rs_977"  "rs_975"  "rs_906"  "rs_938"

#### 3.5.2. Trait-specific (uncolocalized) outcomes (`ucos_outcomes`)

- `ucos_outcomes`: A list with a detailed information about trait-specific (uncolocalized) outcomes for each uCoS.
  - `outcome_index`: Indices of trait-specific (uncolocalized) outcomes.
  - `outcome_name`: Names of trait-specific (uncolocalized) outcomes.

    res$ucos_details$ucos_outcomes
    #> $outcome_index
    #> $outcome_index$`ucos1:y4`
    #> [1] 4
    #>
    #> $outcome_index$`ucos2:y4`
    #> [1] 4
    #>
    #>
    #> $outcome_name
    #> $outcome_name$`ucos1:y4`
    #> [1] "Y4"
    #>
    #> $outcome_name$`ucos2:y4`
    #> [1] "Y4"

#### 3.5.3. Purity across CoS and uCoS (`cos_ucos_purity`)

- `cos_ucos_purity`: Includes three lists, each containing an \(S \times uS\) matrix, where \(S\) is the number of CoS and \(uS\) is the number of uCoS:
  - `min_abs_cor`: Minimum absolute correlation of variables across each pair of CoS and uCoS.
  - `median_abs_cor`: Median absolute correlation of variables across each pair of CoS and uCoS.
  - `max_abs_cor`: Maximum absolute correlation of variables across each pair of CoS and uCoS.

    res$ucos_details$cos_ucos_purity
    #> $min_abs_cor
    #>                    ucos1:y4   ucos2:y4
    #> cos1:y1_y2_y3     0.1132965 0.05866258
    #> cos2:y2_y3:merged 0.1675803 0.03404661
    #>
    #> $max_abs_cor
    #>                    ucos1:y4  ucos2:y4
    #> cos1:y1_y2_y3     0.4111256 0.4507412
    #> cos2:y2_y3:merged 0.5222858 0.5905318
    #>
    #> $median_abs_cor
    #>                    ucos1:y4  ucos2:y4
    #> cos1:y1_y2_y3     0.3633263 0.2969155
    #> cos2:y2_y3:merged 0.3449331 0.3134146

#### 3.5.4. Other components

- `ucos_weight`: Integrative weights for each trait-specific (uncolocalized) trait, used to recalibrate uCoS when traits are filtered out.
- `ucos_top_variables`: Indices and names of the top variable for each uCoS, which is the variable with the highest VCP.
- `ucos_purity`: Includes three lists, each containing an \(uS \times uS\) matrix, where \(uS\) is the number of uCoS:
  - `min_abs_cor`: Minimum absolute correlation of variables within (diagonal) uCoS or between (off-diagonal) different uCoS.
  - `median_abs_cor`: Median absolute correlation of variables within or between uCoS.
  - `max_abs_cor`: Maximum absolute correlation of variables within or between uCoS.

By analyzing these components, you can gain a deeper understanding of trait-specific (uncolocalized) effects that are not colocalized, providing additional insights into the data.

### 3.6. Diagnostic details (`diagnostic_details`)

There is `diagnostic_details` in ColocBoost output when setting `output_level = 3`:

    # Loading the dataset
    data(Ind_5traits)
    X <- Ind_5traits$X
    Y <- Ind_5traits$Y
    res <- colocboost(X = X, Y = Y, output_level = 3)
    #> Validating input data.
    #> Starting gradient boosting algorithm.
    #> Gradient boosting for outcome 4 converged after 40 iterations!
    #> Gradient boosting for outcome 5 converged after 59 iterations!
    #> Gradient boosting for outcome 1 converged after 61 iterations!
    #> Gradient boosting for outcome 3 converged after 91 iterations!
    #> Gradient boosting for outcome 2 converged after 94 iterations!
    #> Performing inference on colocalization events.

- `cb_model`: trait-specific proximity gradient boosting model, including proximity weight at each iteration, residual after gradient boosting, etc.
- `weights_paths`: individual trait-specific weights for each iteration.

    names(res$diagnostic_details$cb_model)
    #> [1] "ind_outcome_1" "ind_outcome_2" "ind_outcome_3" "ind_outcome_4"
    #> [5] "ind_outcome_5"
    names(res$diagnostic_details$cb_model$ind_outcome_1)
    #>  [1] "res"                         "beta"
    #>  [3] "weights_path"                "profile_loglike_each"
    #>  [5] "obj_path"                    "obj_single"
    #>  [7] "change_loglike"              "correlation"
    #>  [9] "z"                           "learning_rate_init"
    #> [11] "stop_thresh"                 "ld_jk"
    #> [13] "jk"                          "z_univariate"
    #> [15] "beta_hat_univariate"         "multi_correction"
    #> [17] "multi_correction_univariate" "stop_null"
    #> [19] "check_null_max"              "beta_hat"

- `cb_model_para`: parameters used in fitting ColocBoost model.

    names(res$diagnostic_details$cb_model_para)
    #>  [1] "L"                     "P"                     "N"
    #>  [4] "tau"                   "func_simplex"          "lambda"
    #>  [7] "lambda_focal_outcome"  "learning_rate_decay"   "profile_loglike"
    #> [10] "dynamic_learning_rate" "prioritize_jkstar"     "jk_equiv_corr"
    #> [13] "jk_equiv_loglik"       "func_compare"          "coloc_thresh"
    #> [16] "update_status"         "jk"                    "LD_free"
    #> [19] "real_update_jk"        "outcome_names"         "variables"
    #> [22] "focal_outcome_idx"     "coveraged"             "num_updates"
    #> [25] "coveraged_outcome"     "num_updates_outcome"   "func_multi_test"
    #> [28] "multi_test_thresh"     "multi_test_max"        "M"
    #> [31] "no_coverage_stop"      "weight_fudge_factor"   "coverage"