Sampling for Detailed NDIP Inspections

Emma O’KeefeStR in Dental Public Health

Presented at NDIP Coordinators’ Study Day 26th July, 2010

(Updated 2014 in relation to sampling at CPP (Community Planning Partnership Level))

Aims & Objectives

• To give a working example of how to carry out sampling at Board Level and CHP or CPP level

Why?

• Consistent• Comparisons• Opportunity to share experiences

Why sample?

• Resources• Necessary• Random and representative• Sufficient size

Sampling protocol

• State maintained schools• Minimum sample of 250 per area• Select additional 15-20%• All children in class• Refresh sample each year

Sampling- Step 1 Board Area Worked example• Lists from Local Education Dept.• Exclusions• 141 schools• 3732 pupils• 216 classes

Example

School + Class

CHP or CPP

Number in Year

Number in Class

A1 X 19 19

A2i Z 51 24

A2ii Z 51 27

A3 Y 31 31

Sampling- Step 2Divide according to school year size• Divide into:• Small (1-15)• Medium (16-49)• Large (50+)

Summary school information No. pupils in school year Total

Small(1-15)

Medium(16-49)

Large(50+)

Year Populatio

n

319 2396 1017 3732

No. of schools

40 84 17 141

Calculate no. of pupils and schools to inspect

Year Size

No. of schools

No. of children

% of Board year

population

Sample required

Small 40 319 8.5 26

Medium 84 2396 64.2 193

Large 17 1017 27.3 82

Total 141 3732 100 301

Sampling Step 3Random numbers 3.1

• Generate random numbers (>0 to <1)

• Select column to input random no.

• Use Σ function (more functions)• Select RAND • Press OK

Sampling Step 3Random numbers 3.2

• Will give random no. in top cell • Select that cell• Click on little box bottom right• Click and drag down column• Populate random no. in all cells

Sampling Step 3Random numbers 3.3

• To set random number values– Highlight random numbers– Copy column– Paste Special– Select Values option– Random numbers will be held

Sampling Step 3Random numbers 3.4

• Each school class assigned random number

• Sort by random no. column

Calculate no. of pupils to inspect

No. pupils in school year Total

Small(1-15)

Medium(16-49)

Large(50+)

Year Population 319 2396 1017 3732Proportion of year population (%)

8.5 64.2 27.3 100

No. of children required to sample

26 193 82 301

Calculate no. of pupils and schools to inspect

Year Size

No. of school

s

No. of children

% of Board year

population

Sample required

No. selected schools (pupils)

Small 40 319 8.5 26 6 (28)

Medium

84 2396 64.2 193 10 (199)

Large 17 1017 27.3 82 4 (88)

Total 141 3732 100 301 20 (315)

Sampling at CHP/CPP Level

• Why?– Local comparisons– Local planning

• How?– Minimum of 250 per CHP/CPP

area– Weighting (carried out by ISD)

Sampling protocol

• State maintained schools• Minimum sample of 250 per

CHP/CPP• Select additional 15-20%• All children in class• Refresh sample each year

Sampling- CHP/CPP worked example

• Lists from Local Education Dept.• Exclusions• 3 CHP/CPP areas• 141 schools• 3732 pupils• 216 classes

CHP/CPP Level

• Sort into separate CHPs/CPPs• Sort by school year size• Allocate random numbers• Sort by random numbers• Select classes to inspect

CHP/CPP pupils in school year

CHP /CPP School Year Size Total

Small Medium Large

X 37 561 468 1066

Y 139 1024 419 1582

Z 143 811 130 1084

Total 319 2396 1017 3732

No. pupils to inspect per class size per CHP/CPP to get sample 300

CHP/CPP School year size Total

Small Medium Large

X 10 158 132 300

Y 26 194 80 300

Z 40 224 36 300

Completed sampling for CHPs/CPPs

No. selected schools (pupils)

Year Size X Y Z

Small 3 (11) 2 (27) 9 (44)

Medium 10 (180) 11 (208) 12 (245)

Large 7 (151) 3 (84) 2 (51)

Total 20 (342) 16 (319) 23 (340)

Weighting

• Results need to be weighted for average for NHS Board area

CHP/CPP Sample size

School Yr % inspected

X 300 1066 28

Y 300 1582 19

Z 300 1084 28

Total for NHS Board

900 3732 24

Reference

• Pine CM, Pitts NB, Nugent ZJ. BASCD Guidance on Sampling for Surveys of Child Dental Health. Community Dental Health 1997; 14 (Supplement 1):10-17.Found www.bascd.org in policy section under guidance dated Friday 23rd January 2004.

Useful websites

• www.scottishdental.org• www.dundee.ac.uk/dhsru• www.bascd.org• www.glac.ac.uk/departments/

dentalschool

Appendix 1- CHP/CPPs