Appendix 1 - The Sample

(1) Method

The sample was designed to represent primarily children under the age of sixteen in England and Wales, and secondarily to represent the mothers of such children.

Appropriate proportions of children were selected in each of five regions, and within each region in large and small towns and in rural districts.

The five regions were as follows:

North , comprising Civil Defence Regions, Nos. 1, 2 and 10.

Midlands & Wales , comprising Civil Defence Regions Nos. 3, 8 and 9.

South & East , comprising Civil Defence Regions Nos, 4, 6, 7 and 12.

London , being Civil Defence Region No. 5.

The names and addresses of children in selected areas were drawn at regular intervals from the National Registration Cards for persons aged under sixteen, and the mothers of these children were visited and interviewed, (The cards are filed in order of the code number on the national identity card.)

If after making repeated calls the interviewer was unable to find the mother at home a name was taken from a substitute list, drawn up in the same manner, and the mother of that child was interviewed instead. 24% of interviews were made with the mothers of children whose names were taken from substitute lists.

Information relating to children was obtained about the particular child selected from the register, and the mothers of the children were regarded as a sample of mothers.

The two populations about which information was wanted, children and mothers, do not of course exactly correspond, many mothers having more than one child. However bias in favour of mothers with large families which might be introduced into the sample of mothers as a result of using this method of sampling was not considered to be of sufficient importance to invalidate the method. No list or register of mothers was available and the procedure adopted seemed to be the only practical one.

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(2) Analyses

Some analyses of the sample are given below. Some of these are not strictly relevant to the purpose of the inquiry but have been included as they may be of interest.

Region	No.	%
North	867	33
Midlands & Wales	672	26
South & East	661	26
London	384	15
TOTAL	2584	100
Type of Area	No.	%
Large towns *	1081	42
Small towns	979	38
Rural areas	524	20
TOTAL	2584	100

* Population over 80,000

Age and Sex of Children

Age	Boys			Girls			Total
	No.	%		No.	%		No.	%
Under 1 year	134	10	42	92	7	43	226	9	43
1 year	104	8		106	8		210	8
2 years	109	8		132	10		241	9
3 years	102	8		120	10		222	9
4 years	100	8		105	8		205	8
5 years	105	8	31	107	8	28	212	8	29
6 - 7 years	166	13		150	12		216	12
8 - 9 years	126	10		102	8		228	9
10 - 11 years	106	8	27	111	9	29	217	8	28
12 - 13 years	112	8		112	9		224	9
14 - 15 years	151	11		132	11		283	9
TOTAL	1315	100		1269	100		2584	100

The proportions of children aged from 0 to 5 years are probably rather higher than they should be. A possible reason for this was noted in the introduction.

Age of Mother	No.	%
Under 25 years	182	17
25 to 29 years	499	19
30 to 34 years	659	25
35 to 39 years	608	24
40 to 44 years	404	16
45 years and over	229	9
Unclassified	3	-
Total	2584	100
Number of children aged under 16 per mother
	No.	%
One	920	26
Two	820	32
Three	475	18
Four	187	7
Five or more	180	7
No information	2	-
TOTAL	2584	100
Education of Mother	No.	%
Elementary only	2107	82
Some higher education	465	18
No information	12	-
Total	2584	100

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Economic Group

Economic group was classified according to the wage rate or salary of the chief wage earner in the family or according to income received from other sources if there was no wage earner.

Group		No.	%
Lower	Up to £3 per week	549	21
Lower	Over £3 to £4 per week	568	22
Middle	Over £4 to £5. 10s. per week	1043	41
Higher	Over £5. 10s. £10 per week	315	12
Higher	Over £10 per week	84	3
	No information	25	1
TOTAL		2584	100

Economic Group by Education

Education of Mother	Economic Group
	Higher		Middle		Lower
	No.	%	No.	%	No.	%
Elementary only	157	40	929	88	1002	89
Some higher education	241	60	109	11	109	10
No information	1		5	1	6	7
TOTAL	399	100	1043	100	1117	100

Information about husband (the fathers of children aged under 16)
	No.	%
Husband living at home	1740	68
Husband away from home	676	26
Husband dead, divorced or separated	163	6
No information	5	-
TOTAL	2584	100

Whether Mother was Working
	No.	%
Working full-time	187	7
Working part-time	214	8
Not working	2174	84
No information	9	1
TOTAL	2584	100

Since mothers who are out at work are more difficult to contact than others, some working mothers may have been missed and substitutes interviewed instead of them.

Do you use a Welfare Clinic?
	No.	%
Yes, regularly	411	16
Yes, occasionally	355	14
Need to use one	882	34
No (never have)	935	36
No information	1	-
TOTAL	2584	100

Have you ever been present at a School Medical Examination?
	No.	%
Yes	1252	48
No	1332	52
TOAL	2584	100

(3) Areas in which interviews were made

North	Midlands & Wales	South & East	London
Gateshead C.B.	Nottingham C.B.	Cromer U.D.	Stepney Met. B.
Whickham U.D.	Market Harborough U.D.	Hitchin U.D.	Bermondsey Met. B.
Stanley U.D.	Worksop M.B.	Newmarket U.D.	Kensington Met. B.
Stockton R.D.	Market Harborough R.D.	Erpingham R.D.	Staines U.D.
Sheffield C.B.	Worksop R.D.	Hitchin R.D.	Surbiton M.B.
Wakefield C.B.	Bingham R.D.	Newmarket R.D.	Wood Green M.B.
Skipton U.D.	Birmingham C.B.	Alton U.D.	Battersea Met. B.
Skipton R.D.	Hereford M.B.	Aylesbury M.B.
Liverpool C.B.	Sutton Coldfield M.B.	Alton R.D.
Salford C.B.	Tamworth M.B.	Aylesbury R.D.
Warrington, C.B.	Hereford R.D.	Bristol C.B.
Darwen M.B.	Swansea C.B.	Crediton U.D.
Bury and Tottington U.D.	Abertillery U.D.	Crediton R.D.
	Neath R.D.	Eastbourne C.B.
Sandbach U.D.	Pontypool R.D.	Ashford U.D.
Warrington R.D.		Hailsham R.D.
Congleton R.D.

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DIPHTHERIA IMMUNISATION

SAMPLING INSTRUCTIONS (Given to Investigators)

We are interviewing mothers of children aged under 16 and the sample will be selected from the National Registration Cards. The Registration Officers have been informed that you are coming and that you will need to have access to the register.

Registration cards for children under 16 are filed in separate boxes from the cards for adults, and you will select a sample of children from these cards and go and interview the mothers of these children.

The method of selecting the sample is similar to that used in the Health Index inquiry of which some of you have had experience.

URBAN AREAS

The Main Sample

When you have made sure which boxes contain the cards for children under 16:-

(1) Measure all blocks of cards in these boxes and record the result in inches. When a tray is not completely full, bring sufficient pressure to bear to make the cards into a solid block before measuring.
(2) Divide the number of inches by the number in your quota, e. g. if the cards measure 210 inches and your quota is 50, divide 210 by 50 210 x 50 = 4 (and 10 over, which can be ignored).
(3) Beginning at the front of the first box, in the example above you would measure four inches along the cards, extract the card nearest to the spot reached, and record the name (including Christian names) and address of the child recorded on that card. Go on extracting cards at four inch intervals until you reach the end of the register. The mothers of the children so selected, form your sample of informants.

Substitutes

As you may not succeed in finding the informants on your main list at home, it will be necessary to make a list of substitutes. This should be one third the size of the main sample, and should be selected by the same method.

To do this multiply your original sampling measurement by three, e.g. in the example above 4 x 3 = 12.

You then need to take cards twelve inches apart, but in order to avoid the cards you have already selected for the main sample, begin an inch from the beginning of the first box. (If the distance between the cards for the main sample is less than an inch, begin nearer the front.)

Use of Substitutes

Substitutes should only be used when informants selected for the main sample cannot be found. If the original informant is out, you should call back at least once before taking a substitute. The substitute taken can be the one on the list living nearest to the original informant.

(In rural areas it may not be practicable to call back, and you may take a substitute after calling on the original informant only once if this is necessary).

Mixed Cards

In some National Registration Offices, Urban and Rural Cards are mixed. When this happens find out first of all how many cards there are for the Urban District, and how many for the Rural District. They may be 15,000 cards in the Urban District and 10,000 in the Rural District. This means that whatever number of cards you take out, 3 Cards out of 5 will be Urban cards, so that if you have an Urban quote of 100, you will find only 60. As you know that 3 cards out of 5 will be Urban, however, you can obtain the quota you want by treating it as 3/5 of the total number of cards you have to select from the register. 100 is 3/5 of 166. You, therefore, obtain your required quote of 100 Urban interviews by taking 166 cards from the register.

RURAL DISTRICTS

As rural districts generally cover a wide area we want to reduce travelling by selecting informants in particular parishes only.

If you have a quota in a rural district you should do as follows.

(1) Multiply your quota by 4, e.g. if you have 40 interviews in a rural district 40 x 4 = 160.
(2) Select this number (160 in the example) of cards, using the same method as for urban areas. Write down the name and postal address of the child on the cards selected, and send this list to Mr. Thomas, who will select a sample and substitute list of the appropriate size for you.
(3) If the Urban and Rural cards are mixed, proceed as described above in urban areas, e.g. if out of a total of 15,000 cards, 10,000 are rural, then two out of five cards will be rural. If your quota, multiplied by four, is 160, you will know that 160 is two fifths of the total number of cards you will have to select. 160 is two fifths of 400. You then divide the total number of inches of cards by 400, and extract cards at intervals of so many inches, writing down only the names on the rural cards selected.
(4) If you have quotas for both the urban and. rural district and the cards, are mixed, first select your rural sample (x 4) as described, and then select the urban sample. It will be simpler to select them separately than to try and do them both at once.

THOSE WITH QUOTAS IN RURAL DISTRICTS SHOULD SELECT THE SAMPLE IN THE RURAL DISTRICTS FIRST, SEND IT TO MR. THOMAS, AND THEN WORK ON THEIR URBAN QUOTAS TILL THE SAMPLE TO BE INTERVIEWED IS RETURNED TO THEM.

GENERAL NOTES

(1) Please be sure to record the Christian names of the children selected as some questions are to be asked with reference to these particular children.
(2) When selecting cards the pink “Permanent Debit” cards should be ignored. They are to do with the replacement of identity cards and are duplicated elsewhere.
(3) If there is a separate file of persons aged under 16 who have entered the district since the last re-registration, this should be included in your measurements.
(4) You should make quite sure which of the addresses on a card is most recent. Their arrangement is sometimes confusing owing to alteration in the layout of the card.

Interviewers working in Sheffield, Liverpool, and Birmingham, will be given special instructions about sampling by postal districts by Mr. Thomas.