poputils

In poputils: Demographic Analysis and Data Manipulation

knitr::opts_chunk$set(
  collapse = TRUE,
  comment = "#>"
)

Aims

poputils contains tools for carrying out common tasks when working with demographic data. Some distinctive features:

• poputils tries to into tidyverse workflows. For instance, poputils functions use data frames for inputs and outputs, use tidyselect methods to specify variables, and follow tidyverse conventions for variable names.
• poputils allows for uncertainty through the use of rvecs. An rvec is an object holding multiple draws from a distribution that behaves similarly to an ordinary R vector.
• Allow users to work directly with age and time labels, based on common set of methods.

Some functions in poputils are designed for data analysts working on demographic datasets. Others are designed for programmers creating functions to be used at data analysts.

Tools for data analysts

Labels

Age

Producers of demographic data follow a wide variety of styles for labeling age groups. poputils contains tools for parsing and manipulating age group labels.

Age label functions in poputils require that age labels belong to one of three types:

• "single". Single years of age, possibly including an open age group, eg "0","81","17","100+"`.
• "five". Five-year age groups, possibly including an open age group, eg "0-4", "80-84", "15-19", "100+".
• "lt". Life table age groups. Like "five", but with the "0-4" age group split into "0" and "1-4".

Age labels created by poputils functions such as age_labels() follow a standard set of rules. Many age labels created using other rules can, however, be parsed by poputils functions,

library(poputils)
library(dplyr, warn.conflicts = FALSE)
tibble(original = c("5 to 9", "5_9", "05-09"),
       reformated = reformat_age(original))

Functions age_lower(), age_upper(), and age_mid() extract information about lower limits, upper limits, and centers of age groups. This can be useful for ordering data

df <- data.frame(age = c("5-9", "0-4", "15-19", "10-14"),
                 population = c(3, 7, 2, 4))
df
df |>
  arrange(age_lower(age))

and plotting

library(ggplot2)
ggplot(df, aes(x = age_mid(age), y = population)) +
  geom_point()

among other things.

Functions combine_age() and set_age_open() can be used to collapse age groups,

tibble(age = age_labels("lt", max = 30),
       age_5 = combine_age(age, to = "five"),
       age_25plus = set_age_open(age, lower = 20))

The aim is that users should be able to with age group labels throughout the analysis.

Sex/gender

Function reformat_sex() converts sex/gender categories to "Female", "Male", and any additional categories specified through the except argument,

reformat_sex(c("M", "F", "Diverse", "Fem"), except = "Diverse")

Life tables and life expectancy

A life table a way of summarizing mortality conditions. It consists of quantities calculated from age-specific mortality rates. The most widely-used life table quantity is life expectancy at birth.

Basic functionality

Life tables can be calculated from age-specific mortality rates using function lifetab().

nzmort |>
  filter(year == 2022,
         gender == "Female") |>
  lifetab(mx = mx)  

lifetab() and lifeexp() both have a by argument. Separate results are calculated for each combination of the by variables,

nzmort |>
  lifeexp(mx = mx,
          by = c(gender, year))  

The same effect can be obtained using dplyr::group_by(),

nzmort |>
  group_by(gender, year) |>
  lifeexp(mx = mx)

The input data for life tables and life expectancies can be probabilities of dying (qx), rather than mortality rates (mx)

west_lifetab |>
  group_by(level, sex) |>
  lifeexp(qx = qx)

By default, lifeexp() calculates life expectancy at age zero. It can, however, be used to calculate life expectancy at other ages.

nzmort |>
  lifeexp(mx = mx,
          at = 65,
          by = c(gender, year))  

Calculation methods

Alternative methods for calculating life tables differ mainly in their assumptions variation within age groups [@preston2001demography; @keyfitz2005applied]. It turns out that, for the purposes of constructing life tables, all the relevant information about the way that mortality varies by age within each age group can be captured by a single number: the average length of time lived in an interval by people who die in that interval [@preston2001demography, p.43]. This number is denoted $na_x$, where $x$ is exact age at the start of the internal, and $n$ is the length of the interval. The quantity $_5a{20}$, for instance, refers to the average number of years lived after their 20th birthday by people who die between their 20th and 25th birthdays. When $n=1$, the $n$ subscript is typically omitted.

Functions lifetab() and lifeexp() have four arguments for specifying calculation methods:

• infant, which specifies how $a_0$ is calculated,
• child, which specifies how $_4a_1$ is calculated,
• closed, which specifies how $_na_x$ for all other closed intervals are calculated, and
• open, which specifies how the final interval, $_{\infty}a_x$ is calculated.

Different choices of method are available for each argument. In some cases, different formulas are used for females and males. The formulas can also differ depending on whether the input data is of mortality rates or probabilities of dying.

| argument | sex | method | input | formula | | :------- | :------- | :------------- |:-----:|:-----------------------------------------------------------:| | infant | \<any> | "constant" | mx | $$a_0 = \frac{1 - (m_0 + 1) e^{-m_0}}{m_0 (1 - e^{-m_0})}$$ | | infant | \<any> | "constant" | qx | $$a_0 = \frac{(1 - \log(1 - q_0) (1 - q_0)) - 1}{\log(1 - q_0) q_0}$$ | | infant | \<any> | "linear" | mx | $$a_0 = 0.5$$ | | infant | \<any> | "linear" | qx | $$a_0 = 0.5$$ | | infant | Female | "CD" | mx | $$a_0 = \begin{cases} 0.053 + 2.8 m_0 & 0 \le m_0 < 0.107 \ 0.35 & m_0 \ge 0.107 \end{cases}$$ | | infant | Female | "CD" | qx | $$a_0 = \begin{cases} 0.05 + 3 q_0 & 0 \le m_0 < 0.1 \ 0.35 & q_0 \ge 0.1 \end{cases}$$ | | infant | Male | "CD" | mx | $$a_0 = \begin{cases} 0.045 + 2.684 m_0 & 0 \le m_0 < 0.107 \ b0.33 & m_0 \ge 0.107 \end{cases}$$ | | infant | Male | "CD" | qx | $$a_0 = \begin{cases} 0.0425 + 2.875 q_0 & 0 \le q_0 < 0.1 \ 0.33 & q_0 \ge 0.1 \end{cases}$$ | | infant | Female | "AK" | mx | $$a_0 = \begin{cases} 0.14903 - 2.05527 m_0 & 0 \le m_0 < 0.01724 \ 0.04667 + 3.88089 m_0 & 0.01724 \le m_0 < 0.06891 \ 0.31411 & m_0 \ge 0.06891 \end{cases}$$ | | infant | Female | "AK" | qx | $$a_0 = \begin{cases} 0.149 - 2.0867 q_0 & 0 \le q_0 < 0.017 \ 0.0438 + 4.1075 q_0 & 0.017 \le q_0 < 0.0658 \ 0.3141 & q_0 \ge 0.0658 \end{cases}$$ | | infant | Male | "AK" | mx | $$a_0 = \begin{cases} 0.14929 - 1.99545 m_0 & 0 \le m_0 < 0.023 \ 0.02832 + 3.26021 m_0 & 0.023 \le m_0 < 0.08307 \ 0.29915 & m_0 \ge 0.08307 \end{cases}$$ | | infant | Male | "AK" | qx | $$a_0 = \begin{cases} 0.1493 - 2.0367 q_0 & 0 \le q_0 < 0.0226 \ 0.0244 + 3.4994 q_0 & 0.0226 \le q_0 < 0.0785 \ 0.2991 & q_0 \ge 0.0785 \end{cases}$$ | | child | \<any> | "constant" | mx | $$4a_1 = \frac{1 - (4 \times {_4}m_1 + 1) e^{-4 \times {_4}m_1}}{_4m_1 (1 - e^{-4 \times {_4}m_1})}$$ | | child | \<any> | "constant" | qx | $$_4a_1 = \frac{4((1 - \log(1-{_4}q_1)) (1 - {_4}m_1) - 1)}{\log(1 - {_4q_1}) {_4}q_1}$$ | | child | \<any> | "linear" | mx | $$_4a_1 = 2$$ | | child | \<any> | "linear" | qx | $$_4a_1 = 2$$ | | child | Female | "CD" | mx | $$_4a_1 = \begin{cases} 1.522 - 1.518 m_0 & 0 \le m_0 < 0.107 \ 1.361 & m_0 \ge 0.107 \end{cases}$$ | | child | Female | "CD" | qx | $$_4a_1 = \begin{cases} 1.542 - 1.625 q_0 & 0 \le q_0 < 0.1 \ 1.361 & q_0 \ge 0.1 \end{cases}$$ | | child | Male | "CD" | mx | $$_4a_1 = \begin{cases} 1.651 - 2.816 m_0 & 0 \le m_0 < 0.107 \ 1.352 & m_0 \ge 0.107 \end{cases}$$ | | child | Male | "CD" | qx | $$_4a_1 = \begin{cases} 1.653 - 3.013 q_0 & 0 \le q_0 < 0.1 \ 1.352 & q_0 \ge 0.1 \end{cases}$$ | | closed | \<any> | "constant" | mx | $$_na_x = \frac{1 - (n \times {_n}m_x + 1) e^{-n \times {_n}m_x}}{_nm_x (1 - e^{-n \times {_n}m_x})}$$ | | closed | \<any> | "constant" | qx | $$_na_x = \frac{n((1 - \log(1 - {_n}q_x))(1 - {_nq_x}) - 1)}{\log(1 - {_nq_x}) {_n}q_x}$$ | | closed | \<any> | "linear" | mx | $$_na_x = 0.5 n$$ | | closed | \<any> | "linear" | qx | $$_na_x = 0.5 n$$ | | open | \<any> | "constant" | mx | $${\infty}a_{\omega} = \frac{1}{{\infty}m{\omega}}$$ | | open | \<any> | "constant" | qx | $${\infty}a{\omega} = \frac{1}{{n}m{\omega-n}}$$ |

In the table above, the values for "CD" are from @coale1983regional, p20, and @preston2001demography, p48; the values for "AK" are from @andreev2015average, p376, and @wilmoth2021methods, p37; and the values for "constant" are expected values for an exponential distribution that has been right-truncated at $n$.

When the inputs data are $_nq_x$, the value of $_na_x$ for the last age group is based in mortality rates in the second-to-last age group. This is an expedient to deal with the fact that $_nq_x$ is always 1 in the last age group, and therefore provides no information about mortality conditions in that age group.

Once the $_na_x$ have been determined, the life table is fully specified, and the required calculations can be carried out with no further input from the user.

The probability of dying within each interval is

$$nq_x = \frac{n \times {_n}m_x}{1 + (n - {_n}a_x) \times {_nm_x}},$$ with ${\infty}q_{\omega} = 1$. Quantity $l_x$ is the number of people surviving to exact age $x$. In lifetab(), by default, $l_0 = 100,000$. Remaining values are calculated using

$$l_{x+n} = (1 - {_nq_x}) \times l_x.$$ Quantity $_nd_x$ is the number of people who die between exact ages $x$ and $x+n$,

$$nd_x = l_x - l{x+n}.$$

Quantity $_nL_x$ is the number of person-years lived between exact ages $x$ and $x+n$. It consists of person-years lived by people who survive the interval, plus person-years lived by people who die within the interval,

$$nL_x = l{x+n} \times n + {nd_x} \times {_na_x}.$$ Finally, $e_x$, the number of years of life remaining to a person aged exactly $x$, is $$e_x = {_nL_x} + {_nL{x+n}} + \cdots + {{\infty}L{\omega}}$$.

Although the results for lifetab() and lifeexp() do vary with difference choices for infant, child, or closed, the differences are often small,

lin <- nzmort |>
  lifeexp(mx = mx,
          by = c(gender, year),
          infant = "linear",
          suffix = "lin")
ak <- nzmort |>
  lifeexp(mx = mx,
          sex = gender,
          by = year,
          infant = "AK", 
          suffix = "ak")
inner_join(lin, ak, by = c("year", "gender")) |>
  mutate(diff = ex.lin - ex.ak)

Uncertainty

The examples of life tables and life expectancy so far have all been based on a deterministic input, mx column of data frame nzmort,

nzmort

The data frame nzmort_rvec instead uses a rvec to represent mortality rates,

library(rvec)
nzmort_rvec

The mx rvec holds 1000 draws from the posterior distribution from a Bayesian model of mortality. The posterior distribution for infant mortality for females in 2021, for instance, has a posterior median of 0.0032, and a 95% credible interval of (0.0028, 0.0037).

If the input to lifetab() or lifeexp() is an rvec, then the output will be too. Uncertainty about mortality rates is propagated through to quantities derived from these rates.

library(rvec)
nzmort_rvec |>
  filter(year == 2022,
         gender == "Female") |>
  lifetab(mx = mx) |>
  select(age, qx, lx)

Tools for developers

poputils provides some functions that developers creating packages to be used by demographers may find useful.

Labels

check_age() and age_group_type() can be useful in functions that involve age group labels. check_age() performs some basic validity checks, while age_group_type() assesses whether a set of labels belongs to type "single", "five", or "lt".

It is often possible to guess the nature of a demographic variable, or of categories within a demographic variable, based on names and labels. Functions find_var_age(), find_var_sexgender(), find_var_time(), find_label_female(), and find_label_male() help with these sorts of inferences.

Data manipulation

Function groups_colnums() is helpful when implementing tidyselect methods when the data are held in a grouped data frame.

matrix_to_list_of_cols() and matrix_to_list_of_rows() convert from matrices to lists of vectors.

to_matrix() converts a data frame to a matrix. The data frame potentially has more than two classification variables, and the rows and/or columns of the matrix can be formed from combinations of these variables.

Future developments

Definite

• Stable populations. Given mortality and fertility profiles, generate the associated stable population.
• Time labels Functions for dealing with time labels analogous to the existing ones dealing with age labels. The functions need to allow for one-month and one-quarter periods, and for 'exact times', ie dates.
• Multiple decrement life tables Extend lifetab() and lifeexp() to allow for multiple decrements.
• Projection accounting Functions to turn projected demographic rates, and an initial population, into a projected demographic account. Needs flexibility over dimensions included, and needs deterministic and probabilistic versions.
• TFR Function to calculation total fertility rates from age-specific fertility rates
• Age, period, cohort labels Functions to allocate events to age groups, periods, or cohorts, based on data on dates of event and dates of birth.

Possible

• Aggregation function Using dplyr::count(), dplyr::summarise(), or stats::aggregate() to aggregate counts or rates in a data frame is awkward. Given that this is such a common operation, it might be worthwhile to do a replacement.

References

poputils documentation built on Sept. 14, 2024, 9:07 a.m.