Population variance and ability to suppress computation of standard errors

[tzoltak]

Hi!

• I added two functions: survey_var and survey_sd allowing computation of population variance and standard deviation (with svyvar underneath). I also added some basic tests of this functions to test_survey_statistics.r.
• I patched all the survey_ functions, so it is possible to suppress computation of (any kind of) standard errors (resolving Calculating contingency tables without showing SE #45 ). And I also added drop=FALSE to one row in summarise.grouped_svy so it is able to carry on with such results.
• I made survey_median don't add "_q50" suffix to names of all the variables it generates.
• I made some assertion checks and error messages among survey_ functions a little more consistent.

Hope it will be somehow helpful.

[gergness]

Wow, awesome, thank you so much! I'll take a look in the next week or so!

[codecov-io]

Codecov Report

Merging #48 into master will increase coverage by 1.72%.
The diff coverage is 90.9%.

@@            Coverage Diff             @@
##           master      #48      +/-   ##
==========================================
+ Coverage   79.44%   81.17%   +1.72%     
==========================================
  Files          17       17              
  Lines         905      956      +51     
==========================================
+ Hits          719      776      +57     
+ Misses        186      180       -6

Impacted Files	Coverage Δ
R/summarise.r	88.57% <100%> (ø)	⬆️
R/survey_statistics_helpers.R	83.59% <100%> (+1.97%)	⬆️
R/survey_statistics.r	90.37% <90%> (+3.91%)	⬆️

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[tzoltak]

I hope to implement joins (apart of full join and right join) in the future - they're reasonable if only there is no one-to-many relations between survey object data and data that is to be joined. So this is something that has to be checked before doing actual join and if such relations are found, it will throw an error. With inner, semi and anti joins subsetting of the survey design information must be also implemented but it won't be hard to do with all the functions that are already in the package.

[gergness]

Well, not quite one week, sorry about that!

This is great, but a few minor comments. Do you have time to fix them? I really appreciate it.

[tzoltak]

I can fix this issues tomorrow evening.

[tzoltak]

I didn't manage yesterday - I started to rewrite tests regarding survey_quantile() and survey_median a little (I checked how to get SE from objects returned by svy_quantile) and also I want to add tests to cover calls to functions in survey_statistics.r that result in errors thrown on assertion stage (missing x in case of non-grouped objects and factor/character x). However I'll be working on this today and perhaps tomorrow (if some other things don't let me spend enough time on this today).

Regarding CI for survey_var I thought about and changed my mind: if srvyr is a kind of front-end for survey, perhaps we shouldn't try to be wiser than survey is. If it is possible to obtain CI for variance in survey (in fact it is) and this CI is estimated using t (or normal with df=Inf) distribution - let it be. We may write a warning in description within help page of survey_var that such CI can be a very poor one (especially when analyzing subgroups) but nothing more.
What do you think about this?

[gergness]

No worries, thanks for the update!

Yeah that makes a lot of sense to me, I’ve generally tried to defer the statistical reasoning to the survey package, as it makes support easier. A warning in the documentation seems like a reasonable compromise to me.

[gergness]

Ugh, sorry that took me so long, it's been a month of sickness in my house.

Thank you so so much for your work!

[tzoltak]

Great! :)
Perhaps you should only tidy up version number, because in my pull request it was a rather provisional one.

[gergness]

Yep, will do a full CRAN release soon