I know, I know. Fogginess is part of what we look for in a Golden Age detective novel, if, by “Fogginess”, we mean the ability to cast a swirling haze of mystery over a labyrinthine plot so that we can be taken by surprise when the denouement looms shockingly out of the mist and upsets our every preconception of what has been going on up to that point.

But that’s not the type of “Fogginess” to which I refer.

Instead, I am concerned with the received wisdom that Agatha Christie wrote, for want of a better expression, “pulp fiction” but others, notably Dorothy L.Sayers, wrote, according to some at least, “literature”. I want to test whether that is true, and, if so, to what extent.

Measuring quality is surely an oxymoron. But that is what I am setting out to do. Quality of writing is, you might argue, a matter of style, of how the content is presented to the reader, and, of course, some ineffable something about the actual content itself. One can imagine Oscar Wilde or P. G. Wodehouse concocting aphorisms which positively ooze style but which on closer examination are found to be quite deliberately empty.

Yet there is a measure which might serve my purpose: the Gunning Fog Index. This elegant device neatly sidesteps questions of quality and considers matters purely from the perspective of the reading age it requires of the reader to enable them to make head nor tail of what is written.

My hypothesis is that a work of “literature” is more demanding to read than is a work of “pulp fiction”.

Put another way: a work of pulp fiction will be easier to read than a work of literature. The former might be read by a person with a reading age of 12 whereas the latter might require a person with a reading age of 18 or more.

For those who are interested, I include at the end a note on how the Gunning Fog Index is calculated but it is sufficient for our purposes to observe that writing which uses long sentences and long words is more demanding than writing which uses short sentences and short words. It is not for no reason that our earliest childhood books are filled with sentences like, “The cat sat on the mat.”

The rather brilliant Robert Gunning devised the Index in the early 1950s (so it’s not strictly a Golden Age creation) and it estimates how many years of schooling a given text demands of its readers to make sense of it. Thus a text with a Gunning Fog Index of 8 demands some eight years of schooling for its readers to make sense of it – i.e. it can generally be understood by a high school teenager. This is regarded as the benchmark for a piece to be “universally accessible”. A piece with a Gunning Fog Index of 12 or above, on the other hand, assumes a level of reading equivalent to university education.

On which basis, one might expect that Agatha Christie would have a lower Gunning Fox Index score for her writing than more supposedly literary contemporaries such as Dorothy L. Sayers or Anthony Berkeley.

The difficulty, of course, is that writers will tend to adapt their style, to a greater or lesser extent, to fit their supposed market. Think Roald Dahl. His style for his children’s book Charlie and the Chocolate Factory would be very different from that he employed in Kiss, Kiss, his collection of adult short stories.

Which is where the Detection Club comes into its own. During the 1930s, members of the Detective Club wrote a number of collaborative novels. Therefore, anything included in any one of these novels is, perforce, aimed at the same intended target audience. So a head to head comparison of the various sections of the five books written collectively by the different authors gives a direct and valid comparison of the complexity of their writing given each is writing for the same audience with the same purpose in mind.

The first collaboration by members of the Detection Club was Behind The Screen, published in 1930. This was written by E. C. Bentley, Anthony Berkeley, Agatha Christie, Ronald Knox, Dorothy L. Sayers and Hugh Walpole.

The chart below shows the Fog Index of each of the authors measured from a sample page selected at random from each of their contributions.

It is notable that Agatha Christie and Ronald Knox use a markedly simpler style than do Anthony Berkeley, Dorothy L. Sayers and Hugh Walpole. The contributions by Christie and Knox might be read and understood by an 11 year old (assuming 5-6 years of schooling starting at age 5). Note however, that even the most complex style of Anthony Berkeley, demands a reading age of less than 14.

From which we conclude that Behind The Screen was intended for a universal audience and we see evidence to support the theory that Agatha Christie’s style was less demanding (and therefore arguably, less self-consciously literary) than that of her contemporaries Berkeley, Sayers and Walpole.

But is this pattern repeated in the next collaboration, The Scoop, published in 1931?

Inevitably, of course, we are faced with a different collection of writers in this second story: E. C. Bentley, Anthony Berkeley, Agatha Christie and Dorothy L. Sayers remain but Knox and Walpole are replaced by Freeman Wills Crofts and Clemence Dane.

Here we see that there has been a distinct upward shift in the demands placed with all contributors aiming at a reading age of 12 and above.  Bentley has seen a marked shift upward to a Fog Index of 9.6, implying a reading age of over 14.  More surprisingly, for our theory that Sayers’ writing is more demanding of its readers than Christie’s we find that Sayers has a Fog Index of 6.0 (down from 8.0 in Behind The Screen) whereas Christie has a Fog Index of 6.9 (up from 5.6 in Behind The Screen).  The evidence of this second book, therefore, contradicts the theory that Sayers is a more demanding, and hence by implication, more literary writer than Christie.

Which brings us to the third, and arguably most famous collaborative effort: The Floating Admiral, also published in 1931. Once again we see Berkeley, Christie and Sayers amongst the usual suspects, penning sections of the novel. This time they are joined by a host of others: G. K. Chesterton, G. D. H. And M. Cole, Freeman Wills Crofts (again), Clemence Dane (once again), Edgar Jepson, Milward Kennedy, Ronald Knox (another return), John Rhode, Henry Wade and Victor L. Whitechurch.

Now here things, as they say, start to get really interesting. Firstly we see a far greater inconsistency in style (in terms of the reading age at which each writer pitches his or her chapter). We have Clemence Dane, for example, “upping his game” (or should that be “her game” given this is the pseudonym of playwright Winifred Ashton) and writing a chapter with a Fog Index of 11.8 (demanding a reading age of about 17) while G. D. H. and M. Cole have a Fog Index of a mere 4.8 (making it readable by the typical 10 year old).

It is perhaps unsurprising that G. K. Chesterton’s prologue is demanding on its readers but we also see Dorothy L. Sayers rise to a more demanding Fog Index of 11.0 (reading age 16 or over) after the easing off for The Scoop. This leapfrogs Christie whose chapter once again has a Fog Index of 6.9. Perhaps we see here evidence of Christie having perfected a style which is pitched at precisely the level which is readily accessible to and matches her audience’s expectations.

A noteworthy feature though is Berkeley’s contribution which this time has a Fog Index of a mere 6.5 (reading age of less than 12). It appears that he has been making his style less demanding over the course of these three books.

Sadly for us in our efforts at making an ongoing comparison, this is the last collaboration in which Christie participated (don’t be fooled by her name featuring prominently on the covers, Harper Collins, wise to her bank-ability, have included in each volume essays by her which are unrelated to the main titles and not necessarily even written  contemporaneously with them) but as we move on to Ask A Policeman, published in 1933, we still see both Berkeley and Sayers involved. They are joined this time by: Milward Kennedy (again), Gladys Mitchell, John Rhode (again) and Helen Simpson.

Things are more complicated here as the authors involved were writing pastiches using each others’ detectives and so their personal styles may be overlaid with an exaggerated impersonation of their peers’ own styles.

The most remarkable feature of this collaboration is the contribution by Gladys Mitchell (borrowing Helen Simpson’s detective Sir John Saumarez -actually co-created by Simpson and Clemence Dane) which has a Fog Index of 15.2 (implying a reading age of a third year under-graduate student). This may, in fact, reflect the Clemence Dane influence on the style appropriate to that character rather than Simpson’s own, given Dane’s Fog Index of 11.8 in The Floating Admiral). So far out of line with the rest of her collaborators was this chapter that I actually selected a second page at random to double-check the Index score and, in fact, recorded an even higher Index the second time.

It is notable also that Berkeley has returned to a Fog Index of 8.7 which is more consistent with his contributions to Behind The Screen and The Scoop than his simplified style in The Floating Admiral. Mitchell’s contribution aside, his is the most demanding chapter. Sayers has returned to a less demanding style with a Fog Index of 7.6, making her the least consistent (or is that most erratic) of the regular contributors in terms of the fluctuating demands she places on her readers.

And so we come to the final fictional collaboration from the Golden Age Detection Club members, Six Against The Yard, published in 1936.  This features in addition to Berkeley and Sayers – the only authors to appear in all five titles: Margery Allingham (making her debut as a collaborator), Freeman Wills Crofts (making a welcome return), Ronald Knox (likewise) and Russell Thorndike.

I should perhaps mention that I am avoiding contaminating this analysis of the works of fiction with the potentially confusing element that might be introduced should I also bring into consideration the non-fiction true crime essay collection The Anatomy of Murder.

Here Sayers chapter is markedly more demanding than that of any of her collaborators with a Fog Index of 12.9 (requiring a reading age of 18) which is definitely not within the bounds regarded as “universally accessible”.

This is in marked contrast to the other contributors whose chapters range from a Fog Index of 5.4 (Allingham) to 8.5 (Knox) which would make them all accessible to the average reader. Indeed, Berkeley’s chapter has a Fog Index of 6.1, his simplest yet.

Indeed, if each book is considered as a whole, the overall trend has been one of increasingly demanding reading prior to this last book.  However, this upward trend is in part attributable to the high outliers in each of the preceding books (Sayers and Clemence Dane in the 12 author The Floating Admiral and Mitchell in Ask A Policeman).  Indeed, Sayers contribution to Six Against The Yard inflates its overall Fog Index which would otherwise be marginally the lowest of all five books. Overall though, all of the books fall within the reading capabilities of the typical teenager and so might be regarded as “universally accessible” – albeit with difficult chapters!

In all nineteen authors contributed to the five collaborative books published by The Detection Club in the 1930s. The following chart captures the Fog Index for all of their contributions. It is perhaps worth highlighting some key findings of the analysis.

There are certain authors (Chesterton, Dane, Mitchell and Sayers) whose contributions are markedly more “Foggy”. This finding is not inconsistent with the hypothesis that Fogginess is a reasonable proxy for measuring the literary quality of the writing, based on the premise that a more demanding read is likely to be a more satisfying literary experience (I would not venture to put it any more strongly than that).

It also provides evidence to support the assertion that Sayers (and Chesterton) were more literary writers (or at least more demanding of their readers) than was Christie. Indeed, Christie might be said to have found almost the “golden mean” with a consistent Fog Index in a narrow band between 5.6 and 6.9 making her “universally accessible” to potential readers. Sayers on the other hand is less consistent, sometimes writing simply but often, and particularly later when she was becoming more self-consciously literary and contemplating moving away from the prosaic world of Golden Age Detective Fiction, her work was to become significantly more demanding.

Berkeley is perhaps most interesting in that his Fog Index varies quite widely (his lowest Fog Index is 6.1 in Six Against The Yard which follows on immediately from his highest 8.7 in Ask A Policeman giving a variability  almost exactly twice that of Christie). On closer examination this may be an indication of him deliberately adopting different approaches for each piece. His chapter in Six Against The Yard, for example, is written in the tone of American pulp fiction of the time – a hard-boiled/noir voice with simplified delivery in short, sharp sentences and punchy vocabulary which naturally tends to lower the Fog Index.

For those who wish to understand more about the calculations used to derive the Gunning Fog Index, the formula takes into consideration the length of sentences (longer sentences raise the index) and the use of longer words (taken to be those with more than three syllables ignoring any names or other proper nouns).

Fog Index = 0.4 x ((Number of words in sample / Number of sentences in sample ) plus ((Number of words with more than three syllables in sample / Number of words in sample) x 100) )

For example: a sample page of 300 words, in 20 sentences, with 10 words of three or more syllables would have a Fog Index calculated as follows:

Fog Index = 0.4 x ((300/20) + ((10/300)*100))

                   = 0.4 x (15+3.333)

                   = 7.333

The 0.4 used in the calculation is the factor that Gunning decided was appropriate to derive a number that was meaningful in terms of years of education undergone (and hence reading age).

It is an arbitrary measure but, as can be seen from the above analysis of the Detection Club books, it is one that can produce meaningful results.

I should also point out that when carrying out the analysis, I found that several of the authors had a penchant for using semi-colons in their writing where now we would use full-stops. Thus they might have a huge, long sentence with several clauses, punctuated by semi-colons, with each clause capable of standing on its own as a grammatically acceptable sentence. Where I encountered this, I treated these clauses as if they were indeed sentences separated by full-stops for the purposes of calculating the Index. This ensured an approach consistent with current methods of punctuation, which have more or less eradicated the semi-colon from use in the way these Golden Age authors sometimes chose to use it. This approach is, I believe, justified, since readers in the Golden Age would have been habituated to this method of punctuation and would not have struggled with the resulting immense sentences in the way that a modern reader might.

Mark