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I have just carried out an analysis of my data using logistic regression however I am also required to have a descriptive Statistics part in my report. I honestly don't see the point in this and I was hoping that someone might be able to explain why it is necessary.

For example if I plot a histogram of one of my independent continuous variables and it shows normality or it shows skewness how will this add any value to the report?

My data consists of a dependent variable true or false of getting a job and the independent variable is grades in mid-term, grades in final exams, and male or female.

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  • $\begingroup$ If you can't see any value in plotting a histogram of your IVs then maybe you shouldn't do that, but is there any data which you've collected that you do think is of some value to the work you're presenting in the report? $\endgroup$ – Ian_Fin Dec 1 '16 at 9:40
  • $\begingroup$ Hi Ian, I have added some more detail regarding my problem. I am fairly new to statistics and I was just wondering is there a general approach that we take before we carry out logistic regression. $\endgroup$ – user3223190 Dec 1 '16 at 10:01
  • $\begingroup$ I suggest also looking at and possibly including various plots of the data. For example, you might plot final grade vs mid-term grade color-coded by gender and symbol-coded by "got job" and "failed to get job". $\endgroup$ – Emil M Friedman Dec 7 '16 at 19:30
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In my field, the descriptive part of the report is extremely important because it sets the context for the generalisability of the results. For example, a researcher wishes to identify the predictors of traumatic brain injury following motorcycle accidents in a sample from a hospital. Her dependent variable is binary and she had a series of independent variables. Multivariable logistic regression allowed her to produce the following findings:

  • no helmet use adjusted OR = 4.5 (95% CI 3.6, 5.5) compared to helmet use.
  • all other variables were not included in the final model.

To be clear, there were no issues with the modelling. We focus on the value that the descriptive statistics can add.

Without the descriptive statistics, a reader cannot put these findings in perspective. Why? Let me show you the descriptive statistics:

age, years, mean (SD)                  54 (2)
males, freq (%)                       490 (98)
blood alcohol level, %, mean (SD)    0.10 (0.01)
...

You can see from the above that her sample consisted of older, intoxicated males. With this information the reader is able say what, if any, these results can say about injuries in young males or injuries in non-intoxicated riders or in female riders.

Please don't ignore descriptive statistics.

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    $\begingroup$ Nice example. Is it real or made-up? $\endgroup$ – amoeba says Reinstate Monica Dec 1 '16 at 14:15
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    $\begingroup$ Thanks, @amoeba. The numbers and stats are real. However, I changed the topic into traumatic brain injury to protect the innocent. $\endgroup$ – user140401 Dec 1 '16 at 21:44
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    $\begingroup$ So, drunk men riding motorcycles without helmets... Who would have thought you could wind up with a traumatic brain injury? $\endgroup$ – gung - Reinstate Monica♦ Dec 1 '16 at 22:07
  • $\begingroup$ I enjoying a glass of nice Australian red at the time and Bob's your uncle... $\endgroup$ – user140401 Dec 1 '16 at 22:30
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The point of providing descriptive statistics is to characterise your sample so that people in other centres or countries can assess whether your results generalise to their situation. So in your case tabulating the sex, grades and so on would be a beneficial addition to the logistic regression. It is not to enable people to check your assumptions although they may try to do that too.

============== Edit to give links to some guidelines used in health

In the field with which I am familiar, health, there are specific guidelines for reporting. These have been collected together in the EQUATOR network which should be consulted for up to date details.

As an example we may take clinical trials where the relevant guideline is CONSORT. In the document outlining the guideline available here and elsewhere we read in Table 1 recommendation 15 "A table showing baseline demographic and clinical characteristics for each group".

There are similar recommendations for other study types.

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  • $\begingroup$ Thank you mdewey, so when we do the various descriptive plot and if we notice normality or skewness why only merely comment on it. And so basically the descriptive statistics only real use to inform the reader of what data you are working with. Really sorry if this may seem elementary $\endgroup$ – user3223190 Dec 1 '16 at 10:11
  • $\begingroup$ That is the way it works in the health field which is the one with which I am most familiar. $\endgroup$ – mdewey Dec 1 '16 at 12:16
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    $\begingroup$ +1. At first I misread "in other centres or countries" as "in other centuries". $\endgroup$ – amoeba says Reinstate Monica Dec 1 '16 at 14:14
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Another thing is to show how well behaved your variables are. If, for example, one of your variables is the salary, and you have interviewed exactly one billionaire, when you input his salary into the logistic regression is going to dominate over everything else, so you will likely learn to ignore the salary, regardless of how much actual information it may hold.

Some methods are more sensitive than others to skewness and extreme values, and logistic regression is rather on the sensitive side. Of course, the final proof is in the pudding, and you can compare the results obtained with the raw data, or with each feature transformed towards normality.

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A descriptive part helps to understand the reader your dataset. In applied econ it is usually highly recommended as it may show the first potential flaws in your analysis.

You may use data from different sources to blow up your descriptives.

1 table should be enough. The one you attached is not very intuitive.

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