Sickness Experience in England, 1870–1949

Abstract

Using data from the Hampshire Friendly Society, a sickness insurance institution in southern England, we examine morbidity trends in England between 1870 and 1949. Morbidity prevalence increased between 1870 and around 1890, mainly because of a rise in the average duration of sickness episodes, but after 1890 average durations fell markedly even though the incidence of sickness rose. During the first two decades of the twentieth century, sickness prevalence increased gradually, but this rise was entirely due to the greatly increased duration of claims made by men aged 65 years and over. After the early 1920s, both the incidence and the average duration of sickness claims declined. These trends seem to be measuring ‘objective morbidity’: they vary closely with year-on-year changes in the mortality of men of working age, but do not show any clear relationship with real wages or unemployment. Our conclusions are different from those of earlier research using English sickness insurance data. We believe that one reason for this was a methodological problem with the analysis performed by nineteenth-century actuaries.

Appendix: Analysis of the Apparent Increase in the Duration of Sickness Among the Independent Order of Oddfellows Between 1866–1870 and 1893–1897

Where does the idea that the increase in morbidity in the second half of the nineteenth century arose because of the increasing duration of episodes of sickness come from? In this Appendix, we focus on Watson’s report, since this is the weightiest piece of evidence.

Watson’s analysis (Watson 1903, pp. 38–9 and 143–59) was based on person-years of sickness. He classified the person-years according to duration since the episode of sickness began using the duration categories 0–6 months, 6–12 months, 12–24 months and over 24 months. He then compared the actual amount of sickness recorded in each of the duration categories with the amount which would have been expected on the basis of Henry Ratcliffe’s investigation of the Oddfellows’ sickness experience in 1866–1870 (Table 4.4). There are two key observations from this table.

• 1. The increase in morbidity between 1866–1870 and 1893–1897 is very largely a consequence of the increase in the amount of sickness experience recorded at durations over 24 months.

• 2. This increase occurs in all age categories.

Table 4.4 Watson’s results for standardised morbidity in 1893–1897 compared with 1866–1870

We need to explain both these observations.

4.1.1 Sickness Episodes in Progress at the Start of the Investigation

The increase in morbidity at longer durations between 1866–1870 and 1893–1897 was characteristic of all age groups: indeed, it was actually stronger among the younger members than among those aged over 65 years. This matters, because it means that whatever was causing it was affecting all age groups. Explanations such as a replacement of acute conditions by chronic degenerative conditions (Riley 1989, p. 172) are unlikely, as if they were the cause, we should expect the increase in morbidity at longer durations to be concentrated among older members. Riley (1989, p. 192) acknowledges that there was an increase in sickness at all ages and describes this as ‘unsettling’, presumably because it suggests that something other than the conventional epidemiological transition is at work. However, he does not suggest what this might be. Perhaps the same need to posit a cause which would affect all age groups stumped Watson?

It is possible to use Watson’s data to obtain some idea as to the proportion of the apparent increase in the duration of sickness between Ratcliffe’s investigation of 1866–1870 and Watson’s investigation of 1893–1897 which might have been due to the different methods employed by the two men.

Watson provides overall data concerning the amount of sickness observed in his investigation. This was, to the nearest person-year, 52,718 at durations 0–3 months, 12,436 at durations 3–6 months, 11,923 at durations 6–12 months, 12,660 at durations 12–24 months and 45,310 at durations over 24 months, making a total of 135,048 person-years (Watson 1903, p. 141). Consider spells of sickness of durations 0–3, 3–6, 6–12, 12–24 months and 24 months and over. Let the number of spells which last for 24 months or more be l₂₄, and the numbers lasting at least 12, 6 and 3 months be l₁₂, l₆ and l₃, respectively. Let the total number of spells be l₀. Let the person-years of experience in each of Watson’s duration categories be p_0-3, p_3-6, p_6-12, p_12-24 and p₂₄₊, respectively, and let the mean duration of the spells in each duration category be m_0-3, m_3-6, m_6-12, m_12-24 and m₂₄₊ years.

Using standard life table methods, we can show that the following relationships hold:

$$ {p}_{24+}=\left({m}_{24+}-2\right){l}_{24}, $$

$$ {p}_{12-24}={l}_{24}+\left({m}_{12-24}-1\right)\left({l}_{12}-{l}_{24}\right), $$

$$ {p}_{6-12}=0.5{l}_{12}+\left({m}_{6-12}-0.5\right)\left({l}_6-{l}_{12}\right), $$

$$ {p}_{3-6}=0.25{l}_6+\left({m}_{3-6}-0.25\right)\left({l}_3-{l}_6\right) $$

$$ {p}_{0-3}=0.25{l}_3+{m}_{0-3}\left({l}_0-{l}_3\right). $$

Thus, substituting the total number of person-years in each duration category calculated from Watson’s data, we have

$$ 45,310=\left({m}_{24+}-2\right){l}_{24}, $$

$$ 12,660={l}_{24}+\left({m}_{12-24}-1\right)\left({l}_{12}-{l}_{24}\right), $$

$$ 11,923=0.5{l}_{12}+\left({m}_{6-12}-0.5\right)\left({l}_6-{l}_{12}\right), $$

$$ 12,436=0.25{l}_6+\left({m}_{3-6}-0.25\right)\left({l}_3-{l}_6\right) $$

$$ 52,718=0.25{l}_3+{m}_{0-3}\left({l}_0-{l}_3\right). $$

This set of five equations with ten unknowns has many solutions, but there are restrictions on the values of some of the unknowns. We know that there are restrictions on the mean durations of spells in each category. Let us assume that m_0-3 = 0.125 m_3-6 = 0.375 m_6-12 = 0.75 and that m_12-24 =1.5 (i.e. that spells under 3 months long are, on average, 1.5 months long; those between 3 and 6 months long are, on average, 4.5 months long; that spells lasting between 6 and 12 months are, on average, 9 months long; and that spells lasting between 12 and 24 months are, on average, 18 months long). Then the five equations become

$$ 45,310=\left({m}_{24+}-2\right){l}_{24}, $$

(4.A1)

$$ 12,660=0.5\left({l}_{12}+{l}_{24}\right), $$

(4.A2)

$$ 11,923=0.25\left({l}_6+{l}_{12}\right), $$

(4.A3)

$$ 12,436=0.125\left({l}_3+{l}_6\right) $$

(4.A4)

$$ 52,718=0.125\left({l}_0+{l}_3\right). $$

(4.A5)

Since l₀ ≥ l₃ ≥ l₆ ≥ l₁₂ ≥ l₂₄ > 0, then eq. (4.A2) implies that l₂₄ ≤ 12, 660. Substituting this into eq. (4.A1) produces

${m}_{24+}\ge 2+\frac{45,310}{12,660}=5.58$, or that the average duration of spells longer than 24 months’ long is at least 5.58 years.

For simplicity, suppose it is 6 years. With m₂₄₊ = 6, we can solve eqs. (4.A1)–(4.A5) to give

$$ {\displaystyle \begin{array}{l}{l}_{24}=11,328,\\ {}{l}_{12}=13,992,\\ {}{l}_6=33,700,\\ {}{l}_3=65,788,\\ {}{l}_0=355,956.\end{array}} $$

With other values of m₂₄₊ we obtain different solutions (Table 4.5).

Table 4.5 Numbers of spells with durations greater than 0, 3, 6, 12 and 24 months according to mean length of spells over 24 months’ long

We now need to consider the impact of the difference between Watson’s and Ratcliffe’s treatment of the spells ongoing at the start of the period of investigation. A Lexis chart showing the sickness for a set of spells of more than 2 years’ duration illustrates the situation (Figure 4.7). Calendar time is on the horizontal axis, and duration of spell is on the vertical axis. Suppose these spells last m + 2 years and imagine that claims for these sickness spells are made at a rate which is constant over time. Then the person-years of sickness at durations over 2 years during the period of investigation are represented by the area of the rectangle ABDC. This is the person-years calculation used by Ratcliffe in his 1866–1870 investigation. However, the spells under way at the start of the investigation, which are represented by the vertical line AB, will have durations at the start ranging from just above 0 to just under m years distributed uniformly between 0 and m (because of the constant rate of claims). The person-years of sickness before the start of the investigation which they encompass is represented by the area of the triangle ABE. It is this additional sickness which Watson’s approach brings in.

Fig. 4.7

Lexis chart to illustrate difference between Watson and Ratcliffe’s treatment of spells under way at the start of the period of investigation

Note. This chart illustrates the case of m = 6 years

The ratio between Watson’s sickness prevalence and Ratcliffe’s sickness prevalence is equal to $\frac{0.5{m}^2+5m}{5m}=\frac{0.5m+5}{5}=\frac{m}{10}+1$. So, if the average length of spells of over 2 years duration is 6 years (the minimum that Watson’s own figures allow), then, relative to Ratcliffe, he has inflated the sickness in the 24 months and over duration segment by 1.4 times. If the average length is 10 years (by no means impossible given Watson’s data), the inflation factor is 1.8 times., and if the average length is 14 years, it will be 2.2 times. Note also that this inflation factor is the same for all age groups provided m is the same for all age groups.

There will also be some inflation in the shorter duration segments, but since m is much smaller in these, the extent of the inflation will be much less: indeed, it cannot be more than 5% in the 12–24-month category and 2.5% in the 0–6- and 6–12-month categories.

4.1.2 Watson’s 12-Month ‘Off’ Period

Watson also adopted a 12-month ‘off’ period when compiling his tables (Watson 1903, p. 15). This suggests that he treated a new sickness within 12 months of the previous one as a continuation of the previous one. According to Riley (1997, pp. 172–3), this was different from the treatment by Ratcliffe in earlier investigations. Riley points out, correctly, that this means that comparisons of the incidence of claims between Ratcliffe and Watson are therefore not possible (Watson will record a lower incidence than Ratcliffe). He fails to mention, however, that altering the definition of the ‘off’ period will also have an impact on the duration of claims, and confound the comparison of durations between the two surveys. Watson described this 12-month ‘off’ period as ‘moderately long’ (1903, p. 15). By comparison with shorter ‘off’ periods, it will tend to inflate the number of claims of long duration.

It therefore seems that the different treatment of spells in progress at the start of the investigation by Ratcliffe and Watson is likely to account for a substantial proportion of the apparent increase in morbidity at longer durations. Since Watson’s data show a rise of some 2.4–2.6 times (Table 4.4), then the changed methods account for a minimum of 30% (using the minimum possible duration of sickness episodes over 2 years long which Watson’s own data allow) and could account for close to 100% of the increase, especially if the rather extended ‘off’ period used by Watson is also factored into the calculations. Moreover, since the impact of this change in method is not necessarily age specific, the notable and ‘unsettling’ fact that the apparent increase was roughly the same for all age groups suggests that the changed methods might be the main reason.

4.1.3 Watson’s Treatment of Sickness Claims Spanning More Than One Calendar Year

According to Riley, Watson treated a claim spanning more than one calendar year as several separate episodes, the second and subsequent episodes starting on each 1 January. This will artificially inflate the number of episodes and, when comparing the incidence of claims between Ratcliffe’s and Watson’s surveys, will act in the opposite direction to Watson’s 12-month ‘off’ period.

It will, however, tend to change the distribution of claims by duration, as longer claims are more likely to cross the end of the calendar year and hence to be counted multiple times. Its effect is to increase the proportion of longer claims and, again, to make it look as if the mean duration of claims is rising faster than it actually is. Its effect, though, is likely to be fairly small. Assuming an exponential distribution of claim durations such that the mean claim duration is x years, then the impact on the longest duration claims involves multiplying the number of such claims by a factor which is less than or equal to (1 + x). So if x is, say, 0.2 years, it will involve inflating the number of long claims by no more than 20%.

4.1.4 Conclusion

Table 4.4 reports standardised morbidity ratios of between 238 and 264 in 1893–1897 for claims of over 24 months duration compared with 1866–1870. It seems possible, and may be more likely than not, that the majority of this increase is accounted for by the different methods used by Watson and Ratcliffe in their computations. There are three specific differences, and all will tend to mean that Watson inflates the proportion of claims of longer duration compared with Ratcliffe. It is possible, therefore, that the increase in the average duration of claims reported by these actuaries is entirely artefactual.¹⁷