The average size of all families was 4.7 individuals.

If we consider only those family groups having over 1,000 individuals as being sufficiently large to be representative, we may conclude that families of from three to seven individuals show no progressive increase in influenza incidence with increase in size of the family. But all the available evidence indicates that other things being equal, the age incidence is a very important factor. Its influence will be felt in the subject under consideration, and it will modify the results. Thus, families of one or two are almost invariably adults; families of three are very frequently made up of two adults and a child or infant, while families of from five to seven will be more likely to have a high proportion of young adults—the age period more seriously affected.

The next question arising is whether those families, large or small, which are living in crowded circumstances, are more likely to develop the disease. Arbitrary standards must be chosen as indices of crowding. We have chosen two in order that they may check each other. The first is based upon the number of individuals sleeping in a bedroom. Families are classified as follows: Maximum sleeping in a single bedroom, 1; maximum sleeping in a single bedroom, 2; maximum per bedroom, 3, 4, etc.

The second standard of crowding is based upon the ratio of the number of individuals in the family and the number of rooms occupied. One person living in one room is not crowded; two in two rooms, three in three rooms, four in four rooms, eight in eight rooms, twelve in twelve rooms, are not crowded. Two people living in one room four in two rooms, six in three rooms, twelve in six rooms, are decidedly more crowded. On the contrary, one individual in two rooms, two in four, three in six, four in eight, five in ten, etc. have an unusual amount of room.

The ratios P⁄R are then throughout, ¹⁄₁, ²⁄₁, ½. These are used as dividing lines. All families with ratios higher than ²⁄₁ are classed as very crowded. Families with ratios above ¹⁄₁ up to and including ²⁄₁ are classed as crowded. Families with ratios above ½ up to and including ¹⁄₁ are classed as roomy, and those with ratio of ½ or lower are classified as very roomy.

Classifying all families in all six districts according to these last four degrees of crowding, we find, as is shown by Table V, that there is a progressive increase in the proportion of families with one or more cases of the disease, with increase in the extent of crowding.

According to the standard first described we find as is shown in Table VI that families with three, four and five individuals sleeping in a single room show a progressive increase of incidence over those families with but one or two per bedroom. This again is shown best in the total for all families, but is borne out in a study of each district. These statistics are however of little value for the study of the effect of overcrowding, because crowded families are usually large families. With an influenza incidence of 20 per cent. we would theoretically expect every family of five or larger to have one or more cases. This would amount to 100 per cent. infected families and such a state would not only influence, but dominate the statistics regarding overcrowding.

TABLE V.
Effect of crowding on development of influenza in families.
(A higher proportion of crowded households than roomy are invaded).
(Standard used: ratio of number individuals to number rooms).
Living conditions. No. of such families. Proportion of these families visited by influenza.
In 1918–19. In 1920. In both epidemics (Recurrent). Total families invaded.
No. Per cent. No. Per cent. No. Per cent. No. Per cent.
District I.
V. Cr. 53 30 56.61 15 28.31 12 22.64 31 58.49
Cr. 195 107 54.87 59 30.26 43 22.05 123 63.08
R. 79 36 45.57 24 30.38 18 22.78 42 53.16
V. R. 16 7 43.75 1 6.6 0 0.0 8 50.00
District II.
V. Cr. 4 1 25.00 1 25.00 1 25.00 1 25.00
Cr. 137 70 51.09 31 22.63 2 8.76 89 64.96
R. 208 70 33.65 39 18.75 7 8.17 92 44.23
V. R. 103 20 19.42 7 6.80 2 1.94 25 24.27
District III.
V. Cr. 13 9 69.23 2 15.38 1 7.69 10 76.92
Cr. 213 99 46.48 65 30.52 40 18.78 124 58.22
R. 143 62 43.36 35 24.48 15 10.49 82 57.34
V. R. 21 8 27.59 2 6.89 2 6.89 8 38.09
District IV.
V. Cr. 0 0 0 0 0
Cr. 27 18 66.67 8 29.63 5 18.52 21 77.77
R. 137 72 52.55 50 36.49 21 15.33 101 73.72
V. R. 95 38 40.00 27 28.42 12 12.63 53 55.79
District V.
V. Cr. 6 2 33.33 4 66.67 2 33.33 4 66.67
Cr. 110 67 60.91 37 33.64 25 22.73 79 71.82
R. 209 104 49.76 70 33.49 38 18.18 146 69.86
V. R. 14 3 21.42 3 21.42 0 6 42.84
District VI.
V. Cr. 0 0 0 0 0
Cr. 2 1 50.00 0 0.0 0 0.0 1 50.00
R. 92 57 61.96 23 25.00 14 15.22 66 71.74
V. R. 189 65 34.39 46 24.34 19 10.05 92 48.68
Living conditions.No. of families.No. 1918.Per cent. 1918.No. 1920.Per cent. 1920.No. both.Per cent. both.Total.Per cent.
Very crowded804353.752531.251822.505062.50
Crowded69337253.6820129.0012618.1844764.50
Roomy86539445.5524428.2112514.4551359.31
Very Roomy44314332.288719.64368.1319443.79
AllTotal1918Per cent.1920Per cent.BothPer cent.TotalPer cent.
208195245.7555726.7730514.66120457.86
TABLE VI.
Effect of crowding.
(Standard used: maximum number sleeping in one bed room.)
Maximum No. sleeping per room. No. of such families. Proportion of these families with cases of influenza.
In 1918–19. In 1920. In both epidemics. Total families invaded.
No. Per cent. No. Per cent. No. Per cent. No. Per cent.
District I.
1 16 6 37.50 4 25.00 3 18.75 7 93.75
2 93 52 55.91 31 33.33 20 21.51 63 67.74
3 145 65 44.83 47 32.41 27 18.62 85 58.62
4 79 43 54.43 25 31.65 17 21.52 51 64.56
5 24 11 45.83 11 45.83 6 25.00 16 66.67
6 10 3 30.00 3 30.00 1 10.00 5 50.00
District II.
1 90 15 16.67 7 7.77 2 2.22 20 22.22
2 211 68 32.23 36 17.06 14 6.64 90 42.65
3 115 59 51.30 23 20.00 10 8.69 72 66.61
4 33 20 60.60 11 33.33 6 18.18 25 75.76
5 3 1 33.33 2 66.67 1 33.33 2 66.67
6 0 0 0 0 0
District III.
1 26 10 38.46 3 11.54 2 7.69 11 42.31
2 179 73 40.78 47 26.26 23 12.85 97 54.19
3 145 72 49.66 37 25.52 23 15.86 86 59.31
4 39 20 51.28 15 38.46 8 20.51 27 69.23
5 8 5 62.50 2 25.00 1 12.50 6 75.00
6 0 0 0 0 0
District IV.
1 53 15 28.30 15 28.30 6 11.32 24 45.28
2 165 80 48.48 56 33.94 22 13.33 114 69.09
3 42 29 69.05 15 35.71 10 23.81 34 80.95
4 5 4 80.00 0 0.0 0 0.0 4 80.00
5 0 0 0 0.0 0 0
6 0 0 0 0 0
District V.
1 23 8 34.77 6 26.08 1 4.35 13 56.52
2 156 70 44.37 48 30.77 24 15.38 94 60.26
3 130 81 62.31 44 33.84 27 20.77 98 75.38
4 27 18 66.66 14 51.85 12 44.44 20 74.07
5 6 3 50.00 4 66.67 3 50.00 4 66.67
6 1 0 0.00 0 0.00 0 0.00 0 0.00
District VI.
1 120 42 35.00 24 20.00 10 8.33 56 46.67
2 146 77 52.74 34 23.29 22 15.07 89 60.96
3 10 5 50.00 5 50.00 1 10.00 6 60.00
4 0 0 0 0 0
5 0 0 0 0 0
6 0 0 0 0 0
Total
1 328 96 29.27 59 17.99 24 7.32 131 39.94
2 450 420 44.21 252 26.53 125 13.16 547 57.57
3 587 311 52.98 171 29.13 98 16.69 381 64.91
4 183 105 57.38 65 35.52 43 23.50 127 69.39
5 41 20 48.78 19 46.34 11 26.83 28 68.29
6 11 3 27.27 3 27.27 1 9.09 5 45.45