MR. SPAHLINGER'S SUCCESS
[To the Editor of Tim SPECTATOR.] Loat has criticised your report of the Spahlinger cattle vaccine tests, but she has omitted to mention which of the groups had treatments which were not expected to produce any effect. These were (British Medical Journal) Groups IV and V. Condensed, therefore, the results may be set out in the table :
Not Seriously seriously tuberculous tuberculous Total Inoculated with vaccine 6 13 19 Inoculated with control media or not inoculated .. 8 3 11 Total 14 18 30 The two remaining animals (making the thirty-two of Miss Loat's letter) were used for a preliminary virulence test.
Miss Loat makes the statement that " the numbers are far too small for a statistical test of any significance." This represents a very commonly accepted view, amongst those not acquainted with recent developments in statistics. Actually there are not in existence exact statistical tests which are applicable to many problems involving small numbers of observations, including problems of the above type.
Briefly it can be asserted that if in fact the active vaccine produced no effect whatever, the above set of results, or a set indicating greater association of immunity with innocula- tion, would have occurred by chance only 1 in 28 times. An almost identical value, 1 in 26 times, would have been obtained had the uninoculated Group VI been compared with Group III alone (the " new " vaccine group). The results, therefore, though not completely conclusive, may be taken as indicating some degree of immunisation,• though the num- bers are much too small to assess this degree with any accuracy.
Surely, however, the main point of the results is that the immunity conferred is by no means complete, since tuberculous animals appear in all three groups inoculated with active
vaccine.—Yours faithfully, F. YATES. Rothamsted Experimental Station.
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