eatATA: a Pilot
Study ExampleeatATA efficiently
translates test design requirements for Automated Test Assembly
(ATA) into constraints for a Mixed Integer Linear
Programming Model (MILP). A number of efficient and user-friendly
functions are available that translate conceptual test assembly
constraints to constraint objects for MILP solvers, like the
GLPK solver. In the remainder of this vignette I will
illustrate the typical use of eatATA using a case-based
example. A general overview over eatATA can be found in the
vignette Overview of eatATA
Functionality.
The eatATA package can be installed from
CRAN.
First, eatATA is loaded into the R
session.
No ATA without an item pool. In this example we use a
fictional example item pool of 80 items. The item pool information is
stored as an excel file that is included in the package. To
import the item pool information into R we recommend using
the package readxl. This package imports the data as a
tibble, but in the code below, the item pool is immediately
transformed into a data.frame.
Note that R requires a rectangular data set. Yet, often
excel files store additional information in rows above or below the
“rectangular” item pool information. The skip argument in
the read_excel() function can be used to skip unnecessary
rows in the excel file. (Note that the item pool can also
be directly accessed in the package via items; see
?items for more information.)
items_path <- system.file("extdata", "items.xlsx", package = "eatATA")
items <- as.data.frame(readxl::read_excel(path = items_path), stringsAsFactors = FALSE)Inspection of the item pool indicates that the items have different
properties: item format (MC, CMC,
short_answer, or open), difficulty
(diff_1 - diff_5), average response times in
minutes (time). In addition, similar items can not be in
the same booklet or test form. This information is stored in the column
exclusions, which indicates which items are too similar and
should not be in the same booklet with the item in that row..
head(items)
#> item exclusions time subitems MC CMC short_answer open
#> 1 item_00 item_01, item_06 1.0 1 NA NA 1 NA
#> 2 item_01 item_00, item_06 1.5 1 NA NA 1 NA
#> 3 item_02 item_04, item_63, item_62 2.0 1 NA NA NA 1
#> 4 item_03 <NA> 1.5 1 NA NA 1 NA
#> 5 item_04 item_02, item_63, item_62 1.5 1 NA NA 1 NA
#> 6 item_05 <NA> 1.0 1 NA NA 1 NA
#> diff_1 diff_2 diff_3 diff_4 diff_5
#> 1 1 NA NA NA NA
#> 2 NA 1 NA NA NA
#> 3 NA NA 1 NA NA
#> 4 NA NA 1 NA NA
#> 5 NA 1 NA NA NA
#> 6 1 NA NA NA NABefore defining the constraints, item pool data has to be in the
correct format. For instance, some dummy variables (indicator variables)
in the item pool use both NA and 0 to indicate
“the category does not apply”. Therefore, the dummy variables should be
transformed so that there are only two values (1 = “the category
applies”, and 0 = “the category does not apply”).
Often a set of dummy variables can be summarized into a single factor
variable. This is automatically done by the function
dummiesToFactor(). However, the function can only be used
when the categories are mutually exclusive. For instance, in the example
item pool, items can contain sub-items with different format or
difficulties. As a result, some items contain two sub-items with
different formats. Therefore, in this example, the
dummiesToFactor() function throws an error and cannot be
used.
# clean data set (categorical dummy variables must contain only 0 and 1)
items <- dummiesToFactor(items, dummies = c("MC", "CMC", "short_answer", "open"), facVar = "itemFormat")
#> Error in dummiesToFactor(items, dummies = c("MC", "CMC", "short_answer", : All values in the 'dummies' columns have to be 0, 1 or NA.
items <- dummiesToFactor(items, dummies = paste0("diff_", 1:5), facVar = "itemDiff")
#> Error in dummiesToFactor(items, dummies = paste0("diff_", 1:5), facVar = "itemDiff"): All values in the 'dummies' columns have to be 0, 1 or NA.
items[c(24, 33, 37, 47, 48, 54, 76), ]
#> item exclusions time subitems MC CMC short_answer open diff_1
#> 24 item_23 <NA> 3.5 2 1 1 NA NA NA
#> 33 item_32 item_36 1.5 2 NA NA 2 NA 1
#> 37 item_36 item_27, item_32 1.5 2 NA NA 2 NA 1
#> 47 item_46 item_54, item_44 2.5 2 NA NA 2 NA NA
#> 48 item_47 item_45, item_37 2.0 2 NA NA 2 NA NA
#> 54 item_53 item_43, item_59 2.5 2 NA NA 2 NA NA
#> 76 item_75 <NA> 1.5 2 NA NA 2 NA NA
#> diff_2 diff_3 diff_4 diff_5
#> 24 NA 2 NA NA
#> 33 NA 1 NA NA
#> 37 1 NA NA NA
#> 47 1 1 NA NA
#> 48 NA 1 1 NA
#> 54 1 1 NA NA
#> 76 NA 1 1 NAIn addition, the column short_answer can have NA as a
value, and is consequently not a dummy variable. Therefore, we will (a)
treat short_answer as a numerical value, (b) collapse
MC and open into a new factor
MC_open_none, (these dummies are mutually exclusive), and
(c) turn CMC and the difficulty indicators into factors.
(See ?autoItemValuesMinMax and
?computeTargetValues for further information on the
different treatment of factors and numerical variables.)
# make new factor with three levels: "MC", "open" and "else"
items <- dummiesToFactor(items, dummies = c("MC", "open"), facVar = "MC_open_none")
#> Warning in dummiesToFactor(items, dummies = c("MC", "open"), facVar = "MC_open_none"): For these rows, there is no dummy variable equal to 1: 1, 2, 4, 5, 6, 7, 8, 9, 11, 12, 13, 14, 15, 17, 20, 21, 25, 28, 29, 30, 32, 33, 34, 36, 37, 38, 39, 40, 41, 44, 45, 46, 47, 48, 50, 54, 55, 58, 60, 65, 67, 68, 69, 70, 72, 74, 76, 77, 79, 80
#> A '_none_ 'category is created for these rows.
# clean data set (NA should be 0)
for(ty in c(paste0("diff_", 1:5), "CMC", "short_answer")){
items[, ty] <- ifelse(is.na(items[, ty]), yes = 0, no = items[, ty])
}
# make factors of CMC dummi
items$f_CMC <- factor(items$CMC, labels = paste("CMC", c("no", "yes"), sep = "_"))
# example item format
table(items$short_answer)
#>
#> 0 1 2
#> 34 38 8ATA goalIn this example, the goal is to assemble 14 booklets out of the 80 items item pool. All items should be assigned to one (and only one booklet), so that there is no item overlap and the item pool is completely depleted.
To be more precise, the required constraints are:
no item overlap between test blocks
complete item pool depletion
equal distribution of item formats across test blocks
equal difficulty distribution across test blocks
some items can not be together in the same booklet (item exclusions)
as similar as possible response times across booklets
Note that the booklets will later be manually assembled to test forms.
For ease of use, we set up two variables that we will use frequently:
the number of test forms or booklets to be created (nForms)
and the number of items in the item pool (nItems).
eatATA offers a variety of functions that automatically
compute the constraints mentioned above and which are illustrated in the
following.
First, we are setting up an optimization constraint. This constraint
is not a clear yes or no constraint, and it does not
have to be attained perfectly. Instead, the solver will minimize the
distance of the actual booklet value for all booklets towards a target
value. In our example, we specify 10 minutes as the target response time
time for all booklets.
The first two constraints (no item overlap and item pool depletion)
can be implemented by a single function:
itemUsageConstraint(). To achieve this, the
operator argument should be set to "=",
meaning that every item should be used exactly once in the booklet
assembly.
Constraints with respect to categorical variables or factors (like
MC_open_none) or numerical variables (like
short_answer), can be easily implemented using the
autoItemValuesMinMax() function. The result of this
function depends on whether a factor or a numerical variable is used.
That is, autoItemValuesMinMax() automatically determines
the minimum and maximum frequency of each category of a factor. But for
numerical variables, it automatically determines the target value.
The allowedDeviation argument specifies the allowed
range between booklets regarding the category or the numerical value. If
the argument is omitted, it defaults to “no deviation is allowed” for
numerical values, and to the minimal possible deviation for categorical
variables or factors. Hence, for numeric values, we specify
allowedDeviation = 1. The function prints the calculated
target value or the resulting allowed value range on booklet level.
# item formats
mc_openItems <- autoItemValuesMinMaxConstraint(nForms = nForms, itemValues = items$MC_open_none,
itemIDs = items$item)
#> The minimum and maximum frequences per test form for each item category are
#> min max
#> MC 1 2
#> _none_ 3 4
#> open 0 1
cmcItems <- autoItemValuesMinMaxConstraint(nForms = nForms, itemValues = items$f_CMC, itemIDs = items$item)
#> The minimum and maximum frequences per test form for each item category are
#> min max
#> CMC_no 5 6
#> CMC_yes 0 1
saItems <- autoItemValuesMinMaxConstraint(nForms = nForms, itemValues = items$short_answer,
allowedDeviation = 1, itemIDs = items$item)
#> The minimum and maximum values per test form are: min = 2.86 - max = 4.86
# difficulty categories
Items1 <- autoItemValuesMinMaxConstraint(nForms = nForms, itemValues = items$diff_1,
allowedDeviation = 1, itemIDs = items$item)
#> The minimum and maximum values per test form are: min = 0 - max = 2
Items2 <- autoItemValuesMinMaxConstraint(nForms = nForms, itemValues = items$diff_2,
allowedDeviation = 1, itemIDs = items$item)
#> The minimum and maximum values per test form are: min = 0.57 - max = 2.57
Items3 <- autoItemValuesMinMaxConstraint(nForms = nForms, itemValues = items$diff_3,
allowedDeviation = 1, itemIDs = items$item)
#> The minimum and maximum values per test form are: min = 1.64 - max = 3.64
Items4 <- autoItemValuesMinMaxConstraint(nForms = nForms, itemValues = items$diff_4,
allowedDeviation = 1, itemIDs = items$item)
#> The minimum and maximum values per test form are: min = 0 - max = 1.86
Items5 <- autoItemValuesMinMaxConstraint(nForms = nForms, itemValues = items$diff_5,
allowedDeviation = 1, itemIDs = items$item)
#> The minimum and maximum values per test form are: min = 0 - max = 1.29To implement item exclusion constraints, two function can be used:
itemExclusionTuples() and
itemExclusionConstraint(). When item exclusions are
supplied as a single character string for each item, with item
identifiers separated by ", ", they should be transformed
first.
# item exclusions variable
items$exclusions[1:5]
#> [1] "item_01, item_06" "item_00, item_06"
#> [3] "item_04, item_63, item_62" NA
#> [5] "item_02, item_63, item_62"This transformation can be done using the
itemExclusionTuples() function, which creates so called
tuples: pairs of exclusive items. These tuples can be
used directly with the itemExclusionConstraint()
function.
# item exclusions
exclusionTuples <- itemTuples(items, idCol = "item",
infoCol = "exclusions", sepPattern = ", ")
excl_constraints <- itemExclusionConstraint(nForms = 14, itemTuples = exclusionTuples,
itemIDs = items$item)Another helpful function is the itemsPerFormConstraint()
function, which constrains the number of items per booklet. However,
since this is not required in this example, we will not use these
constraints in the final ATA constraints.
Before calling the optimization algorithm the specified constraints
are collected in a list.
# Prepare constraints
constr_list <- list(itemOverlap, mc_openItems, cmcItems, saItems,
Items1, Items2, Items3, Items4, Items5,
excl_constraints,
av_time)Now we can call the useSolver() function, which
restructures the constraints internally and solves the optimization
problem. Using the solver argument we specify
GLPK as the solver (other alternatives are
lpSolve, Symphony and Gurobi).
Using the timeLimit argument we set the time limit to 10.
This means we limit the solver to stop searching for an optimal solution
after 10 seconds. Note that the computation times might depend on the
solver you have selected.
# Optimization
solver_raw <- useSolver(constr_list, nForms = nForms, nItems = nItems,
itemIDs = items$item, solver = "GLPK", timeLimit = 10)#> [1] "GLPK Simplex Optimizer, v4.47"
#> [2] "1046 rows, 1121 columns, 12824 non-zeros"
#> [3] " 0: obj = 0.000000000e+000 infeas = 4.170e+002 (80)"
#> [4] "* 411: obj = 5.879030940e-001 infeas = 7.963e-016 (0)"
#> [5] "* 438: obj = 2.857142857e-001 infeas = 3.116e-029 (0)"
#> [6] "OPTIMAL SOLUTION FOUND"
#> [7] "GLPK Integer Optimizer, v4.47"
#> [8] "1046 rows, 1121 columns, 12824 non-zeros"
#> [9] "1120 integer variables, all of which are binary"
#> [10] "Integer optimization begins..."
#> [11] "+ 438: mip = not found yet >= -inf (1; 0)"
#> [12] "+ 5675: >>>>> 1.500000000e+000 >= 2.857142857e-001 81.0% (303; 3)"
#> [13] "+ 9322: >>>>> 1.000000000e+000 >= 2.857142857e-001 71.4% (540; 17)"
#> [14] "+ 17425: mip = 1.000000000e+000 >= 2.857142857e-001 71.4% (799; 433)"
#> [15] "+ 26418: mip = 1.000000000e+000 >= 2.857142857e-001 71.4% (1341; 491)"
#> [16] "+ 34686: mip = 1.000000000e+000 >= 2.857142857e-001 71.4% (1850; 551)"
#> [17] "+ 45535: mip = 1.000000000e+000 >= 2.857142857e-001 71.4% (2356; 644)"
#> [18] "+ 54325: mip = 1.000000000e+000 >= 2.857142857e-001 71.4% (2695; 737)"
#> [19] "TIME LIMIT EXCEEDED; SEARCH TERMINATED"
#> The solution is feasible, but may not be optimalThe function provides output that indicates whether an optimal solution has been found. In our case, a viable solution has been found but the function reached the time limit before finding the optimal solution.
If there is no feasible solution, one option is to relax some of the
constraints. Further, for first diagnostic purposes you can omit some
constraints completely, to see which constraints are especially
challenging. If you have a better grasp of the possibilities of the item
pool, you can add these constraints back, but for example with larger
allowedDeviations.
The solution provided by eatATA can be inspected using
the inspectSolution() function. It allows us to inspect the
assembled item blocks at a first glance, including some column sums.
out_list <- inspectSolution(solver_raw, items = items, idCol = "item", colSums = TRUE,
colNames = c("time", "subitems",
"MC", "CMC", "short_answer", "open",
paste0("diff_", 1:5)))
# first two booklets
out_list[1:2]
#> $form_1
#> time subitems MC CMC short_answer open diff_1 diff_2 diff_3 diff_4 diff_5
#> 17 2.0 1 NA 0 1 NA 0 0 0 0 1
#> 19 2.0 1 1 0 0 NA 0 0 0 1 0
#> 27 1.5 1 1 0 0 NA 0 0 1 0 0
#> 41 1.0 1 NA 0 1 NA 0 0 1 0 0
#> 44 1.5 1 NA 0 1 NA 0 1 0 0 0
#> 55 1.0 1 NA 0 1 NA 0 1 0 0 0
#> Sum 9.0 6 NA 0 4 NA 0 2 2 1 1
#>
#> $form_2
#> time subitems MC CMC short_answer open diff_1 diff_2 diff_3 diff_4 diff_5
#> 1 1.0 1 NA 0 1 NA 1 0 0 0 0
#> 10 1.0 1 1 0 0 NA 0 1 0 0 0
#> 20 1.5 1 NA 0 1 NA 0 0 1 0 0
#> 22 2.5 1 1 0 0 NA 0 0 1 0 0
#> 66 2.5 1 NA 0 0 1 0 1 0 0 0
#> 76 1.5 2 NA 0 2 NA 0 0 1 1 0
#> Sum 10.0 7 NA 0 4 NA 1 2 3 1 0In our case we want to assemble the created booklets into test forms.
Therefore, we are interested in booklet exclusions that can result from
item exclusions. The analyzeBlockExclusion() function can
be used to obtain tuples with booklet exclusions.
analyzeBlockExclusion(solverOut = solver_raw, item = items, idCol = "item",
exclusionTuples = exclusionTuples)
#> Name 1 Name 2
#> 1 form_12 form_2
#> 2 form_11 form_2
#> 3 form_11 form_12
#> 4 form_13 form_5
#> 5 form_13 form_4
#> 6 form_13 form_6
#> 7 form_4 form_5
#> 8 form_5 form_6
#> 9 form_12 form_4
#> 10 form_10 form_7
#> 11 form_10 form_13
#> 12 form_10 form_2
#> 13 form_6 form_9
#> 14 form_13 form_3
#> 15 form_13 form_7
#> 16 form_2 form_7
#> 17 form_13 form_2
#> 18 form_11 form_8
#> 19 form_1 form_12
#> 20 form_1 form_14
#> 22 form_12 form_9
#> 23 form_10 form_6
#> 25 form_1 form_10
#> 26 form_13 form_8
#> 27 form_11 form_3
#> 28 form_3 form_4
#> 29 form_5 form_8
#> 32 form_5 form_7
#> 35 form_1 form_3
#> 37 form_1 form_9
#> 38 form_12 form_3
#> 39 form_1 form_6
#> 40 form_12 form_14
#> 41 form_3 form_8
#> 42 form_14 form_3
#> 44 form_4 form_6
#> 45 form_12 form_7To save the item distribution on blocks or test forms, we can use the
appendSolution() function. The function simply merges the
new variables containing the solution to the test assembly problem to
the original item pool.
Finally, when the solution should be exported as an
excel file (.xlsx), this can, for example, be
achieved via the eatAnalysis package, which has to be
installed from Github.