# 3. Methods

#### Yuki Atsusaka and Seo-young Silvia Kim

    library(rankingQ)
    data(identity)

    library(dplyr)
    library(ggplot2)
    library(tidyr)

## Estimating the Proportion of Random Responses

In the `identity` dataset, given `anc_correct_identity`, the raw proportion of those who have correctly or incorrectly answered the anchor question is as follows:

    round(prop.table(table(identity$anc_correct_identity)) * 100, digits = 1)

    ##
    ##    0    1
    ## 30.3 69.7

The 69.7% seen here, however, is likely an upwardly biased estimate of the percentage of non-random responses, because we must account for respondents accidentally answering the question correctly. For an unbiased estimate of random responses, we use `unbiased_correct_prop`.

    identity$random_identity <- case_when(
      identity$anc_correct_identity == 1 ~ 0,
      TRUE ~ 1
    )

    unbiased_correct_prop(
      sum(identity$random_identity == 0) / sum(!is.na(identity$random_identity)),
      J = 4
    )

    ## [1] 0.6836776

The revised estimate of non-random responses is 68.4%. That is to say, roughly 31.6% of the respondents are randomly responding.

## Direct Bias Correction via `imprr_direct`

`rankingQ` has two primary functions to perform bias correction. First, `imprr_direct` improves ranking data by applying direct bias correction to several classes of quantities of interest.

To apply the bias correction, we specify our dataset (`data`), the number of items (`J`), the columns holding the marginal ranks for the target ranking question (`main_q`), and the indicator for answering the anchor ranking question correctly (`anc_correct`). When survey weights are available, they can be included by specifying `weight` in the function.

    ## party, religion, gender, and race hold the marginal rank of each item

    # Perform bias correction
    out_direct <- imprr_direct(
      data = identity,
      ## Not strictly necessary: when `main_q` lists the ranking columns,
      ## J is inferred from their number
      J = 4,
      main_q = c("party", "religion", "gender", "race"),
      anc_correct = "anc_correct_identity",
      # setting to 10 only for our vignette
      n_bootstrap = 10
    )

    ## No weight column supplied; using equal weights for all observations.

By default, `imprr_direct` assumes that the target population is a set of non-random respondents. When researchers wish to study the entire population as a target group, additional arguments must be specified, including `population` and `assumption`. For example, the uniform preference assumption can be specified as follows:

    # Bias correction for the entire population with the uniform assumption

    out_direct_uniform <- imprr_direct(
      data = identity,
      J = 4,
      main_q = c("party", "religion", "gender", "race"),
      anc_correct = "anc_correct_identity",
      population = "all",
      assumption = "uniform",
      n_bootstrap = 10
    )

    ## population = 'all' with assumption = 'uniform' implies no correction; ignoring anc_correct and p_random.

    ## No weight column supplied; using equal weights for all observations.

Similarly, the contaminated sampling assumption can be specified as follows:

    # Bias correction for the entire population with contaminated sampling

    out_direct_contaminated <- imprr_direct(
      data = identity,
      J = 4,
      main_q = c("party", "religion", "gender", "race"),
      anc_correct = "anc_correct_identity",
      population = "all",
      assumption = "contaminated",
      n_bootstrap = 10
    )

    ## No weight column supplied; using equal weights for all observations.

### Results: Estimated Proportion of Random Responses

The first output of `imprr_direct` is the estimated proportion of random responses. The vector `est_p_random` returns the estimated proportion along with the lower and upper ends of its corresponding 95% confidence interval.

    # Estimated proportion of random responses with a 95% CI
    out_direct$est_p_random

    ##        mean     lower     upper
    ## 1 0.3158402 0.2875352 0.3451338

### Results: Estimated Quantities of Interest

The other output is the bias-corrected estimates of four classes of ranking-based quantities, including

1. average ranks
2. pairwise ranking probabilities
3. top-k ranking probabilities
4. marginal ranking probabilities

The output tibble `qoi` stores the estimated quantities and their corresponding 95% CIs.

    # View the results based on the quantity of interest
    out_direct$results %>%
      filter(qoi == "average rank")

    ## # A tibble: 4 × 6
    ##   item     qoi          outcome        mean lower upper
    ##   <chr>    <chr>        <chr>         <dbl> <dbl> <dbl>
    ## 1 gender   average rank Avg: gender    1.66  1.61  1.74
    ## 2 party    average rank Avg: party     3.27  3.21  3.30
    ## 3 race     average rank Avg: race      2.48  2.42  2.53
    ## 4 religion average rank Avg: religion  2.60  2.49  2.66

    # View the results based on the item
    out_direct$results %>%
      filter(item == "party")

    ## # A tibble: 11 × 6
    ##    item  qoi              outcome       mean  lower  upper
    ##    <chr> <chr>            <chr>        <dbl>  <dbl>  <dbl>
    ##  1 party average rank     Avg: party  3.27   3.21   3.30
    ##  2 party marginal ranking Ranked 1    0.0427 0.0309 0.0638
    ##  3 party marginal ranking Ranked 2    0.151  0.133  0.171
    ##  4 party marginal ranking Ranked 3    0.304  0.289  0.336
    ##  5 party marginal ranking Ranked 4    0.503  0.488  0.520
    ##  6 party pairwise ranking v. gender   0.109  0.0807 0.143
    ##  7 party pairwise ranking v. race     0.266  0.257  0.287
    ##  8 party pairwise ranking v. religion 0.359  0.335  0.382
    ##  9 party top-k ranking    Top-1       0.0427 0.0309 0.0638
    ## 10 party top-k ranking    Top-2       0.194  0.172  0.213
    ## 11 party top-k ranking    Top-3       0.497  0.480  0.512

For example, one can visualize the result for average ranks as follows:

    # Plot the result
    out_direct$results %>%
      mutate(
        item = factor(
          item,
          levels = c("party", "religion", "gender", "race")
        )
      ) %>%
      plot_avg_ranking()

## Weighting-Based Bias Correction via `imprr_weights`

The alternative method for bias correction is based on the idea of inverse-probability weighting (IPW). `imprr_weights` improves ranking data by computing bias correction weights, which can be used to correct for the bias in the IPW framework. The same arguments previously used can be used as follows:

Because `imprr_weights` enumerates the full permutation space, its computational cost grows quickly with `J!`. In practice, this method is best suited to small or moderate ranking questions; for larger `J`, `imprr_direct` or `imprr_direct_rcpp` will usually be much more practical.

    # Perform bias correction
    out_weights <- imprr_weights(
      data = identity,
      J = 4,
      main_q = c("party", "religion", "gender", "race"),
      anc_correct = "anc_correct_identity"
    )

    ## No weight column supplied; using equal weights for all observations.

By default, `imprr_weights` assumes that the target population is a set of non-random respondents. When researchers wish to study the entire population as a target group, additional arguments must be specified, including `population` and `assumption`. For example, the uniform preference assumption can be specified as follows:

    # Perform bias correction with the uniform preference assumption
    out_weights_uniform <- imprr_weights(
      data = identity,
      J = 4,
      main_q = c("party", "religion", "gender", "race"),
      anc_correct = "anc_correct_identity",
      population = "all",
      assumption = "uniform"
    )

    ## population = 'all' with assumption = 'uniform' implies no correction; ignoring anc_correct and p_random.

    ## No weight column supplied; using equal weights for all observations.

Similarly, the contaminated sampling assumption can be specified as follows:

    # Perform bias correction with the uniform preference assumption
    out_weights_contaminated <- imprr_weights(
      data = identity,
      J = 4,
      main_q = c("party", "religion", "gender", "race"),
      anc_correct = "anc_correct_identity",
      population = "all",
      assumption = "contaminated"
    )

    ## No weight column supplied; using equal weights for all observations.

### Results: Estimated Weights

The output of `imprr_weights` contains the set of weights for all possible ranking profiles with `J` items. For example, when `J = 4`, the set has `{1234, 1243, ..., 4321}` and each profile now has an estimated weight.

    # View the estimated weights
    out_weights$rankings %>%
      select(ranking, weights)

    ##    ranking   weights
    ## 1     1234 0.0000000
    ## 2     1243 0.0000000
    ## 3     1324 0.0000000
    ## 4     1342 0.0000000
    ## 5     1423 1.0158812
    ## 6     1432 0.4078355
    ## 7     2134 0.8582397
    ## 8     2143 0.8070574
    ## 9     2314 0.7456387
    ## 10    2341 0.0000000
    ## 11    2413 1.1316994
    ## 12    2431 0.5767371
    ## 13    3124 1.0238295
    ## 14    3142 0.5400194
    ## 15    3214 0.8251218
    ## 16    3241 0.0000000
    ## 17    3412 1.2733020
    ## 18    3421 1.0314721
    ## 19    4123 1.2628998
    ## 20    4132 1.1045545
    ## 21    4213 1.0388263
    ## 22    4231 0.4999637
    ## 23    4312 1.2711103
    ## 24    4321 1.0593130

### Results: Estimated PMF with Bias Corrected Data

`imprr_weights` also returns the estimated probability mass function of all ranking profiles before and after bias correction.

    # View the estimated corrected PMF
    out_weights$rankings %>%
      select(ranking, prop_obs, prop_bc)

    ##    ranking    prop_obs     prop_bc
    ## 1     1234 0.012939002 0.000000000
    ## 2     1243 0.010166359 0.000000000
    ## 3     1324 0.012939002 0.000000000
    ## 4     1342 0.006469501 0.000000000
    ## 5     1423 0.046210721 0.046944603
    ## 6     1432 0.018484288 0.007538549
    ## 7     2134 0.033271719 0.028555111
    ## 8     2143 0.030499076 0.024614506
    ## 9     2314 0.027726433 0.020673901
    ## 10    2341 0.005545287 0.000000000
    ## 11    2413 0.064695009 0.073215306
    ## 12    2431 0.022181146 0.012792690
    ## 13    3124 0.047134935 0.048258138
    ## 14    3142 0.021256932 0.011479155
    ## 15    3214 0.031423290 0.025928041
    ## 16    3241 0.011090573 0.000000000
    ## 17    3412 0.126617375 0.161222159
    ## 18    3421 0.048059150 0.049571673
    ## 19    4123 0.118299445 0.149400343
    ## 20    4132 0.059149723 0.065334095
    ## 21    4213 0.048983364 0.050885208
    ## 22    4231 0.020332717 0.010165620
    ## 23    4312 0.124768946 0.158595089
    ## 24    4321 0.051756007 0.054825814

## Estimated Weights with Original Data

    identity_w <- out_weights$results
    head(identity_w)

    ## # A tibble: 6 × 19
    ##   weights s_weight app_identity party religion gender  race anc_identity
    ##     <dbl>    <dbl> <chr>        <dbl>    <dbl>  <dbl> <dbl> <chr>
    ## 1    1.02    0.844 1423             1        4      2     3 1234
    ## 2    1.02    0.886 1423             1        4      2     3 1234
    ## 3    1.27    2.96  3412             3        4      1     2 1234
    ## 4    1.02    0.987 1423             1        4      2     3 1234
    ## 5    1.10    1.76  4132             4        1      3     2 1324
    ## 6    1.02    0.469 3124             3        1      2     4 1234
    ## # ℹ 11 more variables: household <dbl>, neighborhood <dbl>, city <dbl>,
    ## #   state <dbl>, anc_correct_identity <dbl>, app_identity_recorded <chr>,
    ## #   anc_identity_recorded <chr>, app_identity_row_rnd <chr>,
    ## #   anc_identity_row_rnd <chr>, random_identity <dbl>, ranking <chr>

    # save(identity_w, file = "data/identity_w.rda")