EDITORIAL
How to improve your treatment results without really trying Acra Obsrer Gynecol Scand 1992; 71: 575-576
Setting the stage Dear reader, statistics is a wonderful tool. You can tabulate collected figures in rows and columns, add them up into sums and convert them into percentages to permit comparisons between groups of different size. This is elementary. In this letter I shall stick to the simple rules and will not allude to tests of significance, yet demonstrate how, with slight manipulation of figures, you can improve your treatment results to nobody’s benefit but your own. This, you say, is trickery and please keep me out of that sort of unethical activity. Well, I apologize in advance. I really do not suspect you of wanting to cheat. Therefore I shall twist the exercise into a comparison of two groups of patients, each consisting of exactly one hundred women, in which the statistics will be unwittingly distorted, so that everybody’s conscience remains clear. Now,suppose that the two groups of patients are exactly similar with respect to every conceivable trait, so similar that they are indeed one hundred pairs of cloned individuals, all women. Their common feature is cancer of the uterine cervix. For this they have been referred for treatment, the first group of one hundred to one distinguished oncology center, the other (their cloned sisters) to another equally famous institution, anonymized as Hospitals A and B, respectively. To make the imaginary play realistic, we shall assume that all stages of the disease are represented, from localised invasive lesions to extensive tumors with distant metastases. Let us further assume that the oncologists at the two institutions have differing views on treatment, those in Hospital A favoring radical surgery as the primary approach, while those in Hospital B ar more inclined toward irradiation. The choice of treatment will, however, be of no consequence, as the gross results in terms of life and
death at the end of five years from the start of treatment shall be equal in the two groups, as our third precondition. The art of staging
Treatment results are, as often as not, presented by stage of the disease and not as total survival of the whole cohort of patients treated for the condition. It is unfair to refer to poor treatment results for one diagnostic category when the distribution of cases by stage is clearly unfavorable. Grouping tumors into clinical stages at the time of primary treatment better indicates the likelihood of cure within each stage. Survival rates by stage should give a reasonable basis for comparison of results between institutions and between different treatment regimens. It is important that staging is done before treatment and that no patient is reallocated to another stage when surgery reveals that a tumor has a wider extension than originally estimated, because such re-evaluation is not possible if radiation were the primary choice of treatment. Reallocation will therefore invalidate later comparison. So where does the trickery come in? Right here, in the process of staging. Anatomical demarcations of FIGO’s stages 1 , 2 and 3 for carcinoma of the cervix are the vaginal fornices, the parametria and the pelvic wall, and for stage 4 the bladder or rectum. Clearly, here is room for different interpretations of visual and tactile sensations. It is also conceivable that those who prefer radical surgery for stage 1 disease will define a different delimitation than those who prescribe radiation, without any of them consciously cheating. In our comedy of errors, it is unnecessary to take sides. It suffices to record the facts. In Hospital A, 20 of the patients were allocted to stage 1,30 to stage 2, 25 to stage 3 and 25 to stage 4 (Fig. l), while the @ Acta Obstet Gynecol Scand 71 (1992)
576
Editorial
Hospital A
Hospital B
No. of patients Allocated 5- year surylvopf to stage
No.of patients
5 -year su viva1
mL
Allocakd 5 - ar tostpse s u r L s (0 1
5-vear ylrtal
20
18
90%
I 25
22
8 8 yo
II 30
20
67 %
TI 30
18
60 %
Ill 25
11
G bva
m25
10
40 %
H 25
2
n?20
1
5%
Total 100
51
100
51
51 %
1
8%
51 %
figures in Hospital B were 25,30,25 and 20, respectively. Treatment was given according to set rules in each hospital. We skip the intervening years and move directly to: Act V , Scene V
At the end of five years, Hospital A proudly reports survival rates of 90%,67%,44% and 8% in stages 1, 2. 3 and 4, respectively. Hospital B fares slightly worse, with corresponding figures of 88%, 60%, 40% and 5%. But wait: the total number of survivors is the same in the two hospitals! Fifty-one pa-
0 Acta Obster Gynecol Scand 71 (1992)
Fig. I . Five-year survival in two identical groups of patients with carcinoma of ihe uterine cervix. which differ only in one respect: allocation to clinical stages before treatment. This results in slightly poorer survival rates within each stage for Hospital B, giving an illusory effect of substandard treatment.
tients are alive and hopefully free of disease, in each group, thus fulfilling our third precondition that treatment results should be equal. How, then, is it possible for Hospital A to have better results in each of the four stages than Hospital B? The answer is simply that when staging limits are changed consistently in one direction, then stage-specific survival rates will also shift consistently in one direction. This bewildering fact is borne out by the presentation in Fig. 1. Moral: don’t take statistical figures at face value. Try to find out how they were derived. Otherwise you will occasionally be fooled. Per Bergsjfl
How to improve your treatment results without really trying Acra Obsrer Gynecol Scand 1992; 71: 575-576
Setting the stage Dear reader, statistics is a wonderful tool. You can tabulate collected figures in rows and columns, add them up into sums and convert them into percentages to permit comparisons between groups of different size. This is elementary. In this letter I shall stick to the simple rules and will not allude to tests of significance, yet demonstrate how, with slight manipulation of figures, you can improve your treatment results to nobody’s benefit but your own. This, you say, is trickery and please keep me out of that sort of unethical activity. Well, I apologize in advance. I really do not suspect you of wanting to cheat. Therefore I shall twist the exercise into a comparison of two groups of patients, each consisting of exactly one hundred women, in which the statistics will be unwittingly distorted, so that everybody’s conscience remains clear. Now,suppose that the two groups of patients are exactly similar with respect to every conceivable trait, so similar that they are indeed one hundred pairs of cloned individuals, all women. Their common feature is cancer of the uterine cervix. For this they have been referred for treatment, the first group of one hundred to one distinguished oncology center, the other (their cloned sisters) to another equally famous institution, anonymized as Hospitals A and B, respectively. To make the imaginary play realistic, we shall assume that all stages of the disease are represented, from localised invasive lesions to extensive tumors with distant metastases. Let us further assume that the oncologists at the two institutions have differing views on treatment, those in Hospital A favoring radical surgery as the primary approach, while those in Hospital B ar more inclined toward irradiation. The choice of treatment will, however, be of no consequence, as the gross results in terms of life and
death at the end of five years from the start of treatment shall be equal in the two groups, as our third precondition. The art of staging
Treatment results are, as often as not, presented by stage of the disease and not as total survival of the whole cohort of patients treated for the condition. It is unfair to refer to poor treatment results for one diagnostic category when the distribution of cases by stage is clearly unfavorable. Grouping tumors into clinical stages at the time of primary treatment better indicates the likelihood of cure within each stage. Survival rates by stage should give a reasonable basis for comparison of results between institutions and between different treatment regimens. It is important that staging is done before treatment and that no patient is reallocated to another stage when surgery reveals that a tumor has a wider extension than originally estimated, because such re-evaluation is not possible if radiation were the primary choice of treatment. Reallocation will therefore invalidate later comparison. So where does the trickery come in? Right here, in the process of staging. Anatomical demarcations of FIGO’s stages 1 , 2 and 3 for carcinoma of the cervix are the vaginal fornices, the parametria and the pelvic wall, and for stage 4 the bladder or rectum. Clearly, here is room for different interpretations of visual and tactile sensations. It is also conceivable that those who prefer radical surgery for stage 1 disease will define a different delimitation than those who prescribe radiation, without any of them consciously cheating. In our comedy of errors, it is unnecessary to take sides. It suffices to record the facts. In Hospital A, 20 of the patients were allocted to stage 1,30 to stage 2, 25 to stage 3 and 25 to stage 4 (Fig. l), while the @ Acta Obstet Gynecol Scand 71 (1992)
576
Editorial
Hospital A
Hospital B
No. of patients Allocated 5- year surylvopf to stage
No.of patients
5 -year su viva1
mL
Allocakd 5 - ar tostpse s u r L s (0 1
5-vear ylrtal
20
18
90%
I 25
22
8 8 yo
II 30
20
67 %
TI 30
18
60 %
Ill 25
11
G bva
m25
10
40 %
H 25
2
n?20
1
5%
Total 100
51
100
51
51 %
1
8%
51 %
figures in Hospital B were 25,30,25 and 20, respectively. Treatment was given according to set rules in each hospital. We skip the intervening years and move directly to: Act V , Scene V
At the end of five years, Hospital A proudly reports survival rates of 90%,67%,44% and 8% in stages 1, 2. 3 and 4, respectively. Hospital B fares slightly worse, with corresponding figures of 88%, 60%, 40% and 5%. But wait: the total number of survivors is the same in the two hospitals! Fifty-one pa-
0 Acta Obster Gynecol Scand 71 (1992)
Fig. I . Five-year survival in two identical groups of patients with carcinoma of ihe uterine cervix. which differ only in one respect: allocation to clinical stages before treatment. This results in slightly poorer survival rates within each stage for Hospital B, giving an illusory effect of substandard treatment.
tients are alive and hopefully free of disease, in each group, thus fulfilling our third precondition that treatment results should be equal. How, then, is it possible for Hospital A to have better results in each of the four stages than Hospital B? The answer is simply that when staging limits are changed consistently in one direction, then stage-specific survival rates will also shift consistently in one direction. This bewildering fact is borne out by the presentation in Fig. 1. Moral: don’t take statistical figures at face value. Try to find out how they were derived. Otherwise you will occasionally be fooled. Per Bergsjfl
