# 01: Understanding and Preparing Your Event Data

## Overview

The event and population data are at the core of the BYM-based models used in the RSTr package. They work alongside the adjacency information to generate smoothed estimates. In this vignette, we’ll discuss requirements for event and population data and walk through an example with a `data.frame`.

## Requirements

- Data must be a `list` object with names `Y` and `n` for the event counts and for the population counts, respectively;

- `Y` and `n` are intended to be entire-population data. While it is possible to use RSTr to analyze survey data or datasets that don’t include all members of a population of interest, RSTr does not currently allow for the inclusion of survey weights and thus assumes that each `Y / n` is an unbiased estimate of the underlying event rate;

- `Y` and `n` must contain real numbers. Negative and infinite counts are not allowed, but suppressed data containing `NA`’s is acceptable for the `Y` values. Note, however, that `n` must have all population counts;

- For a given CAR model, `Y` must have at least one total event. The CAR model will not be able to smooth information if there is no event data present. For a CAR model, this includes any set of all regions; for an MCAR model, this is any set of all regions and groups; and for the MSTCAR model, this is the entire dataset;

- `Y` and `n` can be up to a three-dimensional array: the first margin (rows) specifies the region, the second margin (columns) specifies the groups of interest, and the third margin (matrix slices) specifies the time period;

- Time periods, regions, and groups must be consistent. If your data contains counts for all regions in a specified set of groups for 1979 and 1981, for example, it must also include counts for all regions and all groups for 1980 as well, even if those counts have zero events;

- Groups of many types are allowed as long as your sociodemographic groups are combined in the appropriate margin. For example, your groups may include just age groups, a mixture of age-sex groups, or even a mix of age-race-sex groups;

- Finally, `Y` and `n` must have dimension names associated with them. This makes for easy identification of counties, groups, and time periods, and is necessary should you want to age-standardize data using RSTr’s additional functionality.

## Example: CDC WONDER dataset

To walk through the data setup from a `data.frame` to the final `array` `list`, we will use data generated by CDC WONDER’s Underlying Cause of Death Compressed Mortality, ICD-9 database, found at https://wonder.cdc.gov/cmf-icd9.html:

    head(maexample)
    #>   Notes Year Year.Code                County County.Code    Sex Sex.Code Deaths
    #> 1       1979      1979 Barnstable County, MA       25001 Female        F     15
    #> 2       1979      1979 Barnstable County, MA       25001   Male        M     57
    #> 3       1979      1979  Berkshire County, MA       25003 Female        F     11
    #> 4       1979      1979  Berkshire County, MA       25003   Male        M     63
    #> 5       1979      1979    Bristol County, MA       25005 Female        F     52
    #> 6       1979      1979    Bristol County, MA       25005   Male        M    191
    #>   Population        Crude.Rate
    #> 1      25239 59.4 (Unreliable)
    #> 2      21261             268.1
    #> 3      24884 44.2 (Unreliable)
    #> 4      22465             280.4
    #> 5      80171              64.9
    #> 6      71943             265.5

Our example dataset contains acute myocardial infarction (ICD-9: 410) mortality and population data in all counties of Massachusetts for men and women aged 35-64 from 1979 to 1981. This dataset also includes some notes in the bottom rows describing the dataset. `maexample` contains several variables:

- `Notes`: Provides general information about the dataset, starting at row 85;

- `Year` and `Year.Code` specify the year;

- `County` and `County.Code` specify the county name and associated FIPS code;

- `Sex` and `Sex.Code` specify the sex group;

- `Deaths` contains our mortality counts of interest;

- `Population` contains our population counts of interest;

- `Crude.Rate` shows the rates per 100,000 in each year-county-sex group. For our purposes, this column can be ignored.

The first thing we want to do with our dataset is remove the notes from the bottom rows - while they are useful for getting acquainted with the dataset, they will ultimately mess up our population arrays. Since `Year` does not have information in rows with notes, we can use that to filter our data:

    ma_mort <- maexample[which(!is.na(maexample$Year)), ]

The above code searches for values in `maexample$Year` that aren’t `NA` and creates a new dataset containing only those rows. Before we start generating our arrays, let’s take stock of how our data is listed out:

    head(ma_mort)
    #>   Notes Year Year.Code                County County.Code    Sex Sex.Code Deaths
    #> 1       1979      1979 Barnstable County, MA       25001 Female        F     15
    #> 2       1979      1979 Barnstable County, MA       25001   Male        M     57
    #> 3       1979      1979  Berkshire County, MA       25003 Female        F     11
    #> 4       1979      1979  Berkshire County, MA       25003   Male        M     63
    #> 5       1979      1979    Bristol County, MA       25005 Female        F     52
    #> 6       1979      1979    Bristol County, MA       25005   Male        M    191
    #>   Population        Crude.Rate
    #> 1      25239 59.4 (Unreliable)
    #> 2      21261             268.1
    #> 3      24884 44.2 (Unreliable)
    #> 4      22465             280.4
    #> 5      80171              64.9
    #> 6      71943             265.5

RSTr offers a `long_to_list_matrix()` function which can transform this dataset into mortality and population arrays with properly oriented margins:

    ma_data <- long_to_list_matrix(ma_mort, Deaths, Population, County.Code, Sex.Code, Year.Code)

If you want to manually set up the data, you can create `Y` and `n` arrays using the `xtabs()` function and consolidate them into a `list` to be used with the model:

    Y <- xtabs(Deaths ~ County.Code + Sex.Code + Year.Code, data = ma_mort)
    n <- xtabs(Population ~ County.Code + Sex.Code + Year.Code, data = ma_mort)
    ma_data <- list(Y = Y, n = n)

Note that you must specify the names of each array element as above, as creating a list with just the objects will not name each element, and the names `Y` and `n` are necessary for RSTr to know how to use the data.

If you have multiple types of groups, such as race and sex, it can take a little finessing to set up your group data, such as creating a combined race-sex group variable, but data setup will follow the same principles as above.

## Data setup for other models

The above dataset is prepared specifically for an MSTCAR model. But what if we want to prepare data for an MCAR or even a CAR model? We can filter the original dataset and follow a similar procedure to prepare our data for the MCAR model:

    ma_mort_mcar <- ma_mort[ma_mort$Year == 1979, ] # filter dataset to only show 1979 data
    ma_data_mcar <- long_to_list_matrix(ma_mort_mcar, Deaths, Population, County.Code, Sex.Code)

Note that `xtabs()` works by aggregating data along the specified variables in the expression argument. In the case of the MCAR model, we filter down to the year we want because otherwise, it would give us the mortality and population counts for all years in our dataset instead of just for 1979.

For the CAR model, setup is similar:

    ma_mort_car <- ma_mort[ma_mort$Year == 1979 & ma_mort$Sex == "Male", ] # filter dataset to only show 1979 data for men
    ma_data_car <- long_to_list_matrix(ma_mort_car, Deaths, Population, County.Code)

## Closing Thoughts

In this vignette, we used data generated from CDC WONDER to construct our event and population counts, remove unnecessary rows using `filter()`, and construct our list using `long_to_list_matrix()`. Setting up the data for RSTr can seem daunting at first, but with a few quick tricks in R, it can be easy to have your data organized for analysis.