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Attachment 13 - Sampling Information
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Attachment 7
Sampling Information
Attachment 7 - Sampling Information
A. Sampling Information Tables
Table 1: Sampling domains and target yearly examination sample sizes for NHANES 2007-2010
Race/ethnicity-sex-age-income sampling domain
Target number of examined SPs
Black, non-Hispanic
M&F
0-11 mos.
50
Black, non-Hispanic
M&F
1-2 yrs.
85
Black, non-Hispanic
M&F
3-5 yrs.
85
Black, non-Hispanic
M
6-11 yrs.
85
Black, non-Hispanic
M
12-19 yrs.
92
Black, non-Hispanic
M
20-39 yrs.
105
Black, non-Hispanic
M
40-49 yrs.
53
Black, non-Hispanic
M
50-59 yrs.
53
Black, non-Hispanic
M
60+ yrs.
105
Black, non-Hispanic
F
6-11 yrs.
85
Black, non-Hispanic
F
12-19 yrs.
85
Black, non-Hispanic
F
20-39 yrs.
105
Black, non-Hispanic
F
40-49 yrs.
53
Black, non-Hispanic
F
50-59 yrs.
53
Black, non-Hispanic
F
60+ yrs.
105
Black, non-Hispanic —Overall
1,197
Hispanic
M&F
0-11 mos.
90
Hispanic
M&F
1-2 yrs.
100
Hispanic
M&F
3-5 yrs.
100
Hispanic
M
6-11 yrs.
100
Hispanic
M
12-19 yrs.
102
Hispanic
M
20-39 yrs.
140
Hispanic
M
40-49 yrs.
70
Hispanic
M
50-59 yrs.
70
Hispanic
M
60+ yrs.
123
Hispanic
F
6-11 yrs.
100
Hispanic
F
12-19 yrs.
102
Hispanic
F
20-39 yrs.
140
Hispanic
F
40-49 yrs.
70
Hispanic
F
50-59 yrs.
70
Hispanic
F
60+ yrs.
147
Hispanic--Overall
1,565
Low Income White/Other
M&F
0-11 mos.
43
Low Income White/Other
M&F
1-2 yrs.
54
Low Income White/Other
M&F
3-5 yrs.
54
Low Income White/Other
M
6-11 yrs.
27
Low Income White/Other
M
12-19 yrs.
27
Low Income White/Other
M
20-29 yrs.
31
Low Income White/Other
M
30-39 yrs.
31
Low Income White/Other
M
40-49 yrs.
31
Low Income White/Other
M
50-59 yrs.
31
Low Income White/Other
M
60-69 yrs.
31
Low Income White/Other
M
70-79 yrs.
31
Low Income White/Other
M
80+ yrs.
20
Low Income White/Other
F
6-11 yrs.
27
Low Income White/Other
F
12-19 yrs.
27
Low Income White/Other
F
20-29 yrs.
31
Low Income White/Other
F
30-39 yrs.
31
Low Income White/Other
F
40-49 yrs.
31
Low Income White/Other
F
50-59 yrs.
31
Low Income White/Other
F
60-69 yrs.
31
Low Income White/Other
F
70-79 yrs.
31
Low Income White/Other
F
80+ yrs.
31
Non-Low Income White/Other
M&F
0-11 mos.
70
Non-Low Income White/Other
M&F
1-2 yrs.
70
Non-Low Income White/Other
M&F
3-5 yrs.
70
Non-Low Income White/Other
M
6-11 yrs.
70
Non-Low Income White/Other
M
12-19 yrs.
71
Non-Low Income White/Other
M
20-29 yrs.
79
Non-Low Income White/Other
M
30-39 yrs.
81
Non-Low Income White/Other
M
40-49 yrs.
82
Non-Low Income White/Other
M
50-59 yrs.
79
Non-Low Income White/Other
M
60-69 yrs.
80
Non-Low Income White/Other
M
70-79 yrs.
79
Non-Low Income White/Other
M
80+ yrs.
70
Non-Low Income White/Other
F
6-11 yrs.
70
Non-Low Income White/Other
F
12-19 yrs.
68
Non-Low Income White/Other
F
20-29 yrs.
75
Non-Low Income White/Other
F
30-39 yrs.
79
Non-Low Income White/Other
F
40-49 yrs.
79
Non-Low Income White/Other
F
50-59 yrs.
75
Non-Low Income White/Other
F
60-69 yrs.
72
Non-Low Income White/Other
F
70-79 yrs.
67
Non-Low Income White/Other
F
80+ yrs.
68
White/Other--Overall
2,238
Overall Total
5,000
Table 2. Expected NHANES 1-year, 2-year, 3-year, and 4-year sample sizes by sampling domain with 15 PSUs per year
Race/ethnicity-sex-age-income sampling domain
1 year
2 year
3 year
4 year
Black, non-Hispanic
M&F
0-11 mos.*
50
100
150
200
Black, non-Hispanic
M&F
1-2 yrs.
85
170
255
340
Black, non-Hispanic
M&F
3-5 yrs.
85
170
255
340
Black, non-Hispanic
M
6-11 yrs.
85
170
255
340
Black, non-Hispanic
M
12-19 yrs.
92
184
276
368
Black, non-Hispanic
M
20-39 yrs.
105
210
315
420
Black, non-Hispanic
M
40-49 yrs.
53
105
158
210
Black, non-Hispanic
M
50-59 yrs.
53
105
158
210
Black, non-Hispanic
M
60+ yrs.
105
210
315
420
Black, non-Hispanic
F
6-11 yrs.
85
170
255
340
Black, non-Hispanic
F
12-19 yrs.
85
170
255
340
Black, non-Hispanic
F
20-39 yrs.
105
210
315
420
Black, non-Hispanic
F
40-49 yrs.
53
105
158
210
Black, non-Hispanic
F
50-59 yrs.
53
105
158
210
Black, non-Hispanic
F
60+ yrs.
105
210
315
420
Black, non-Hispanic--Overall
1,197
2,394
3,591
4,788
Hispanic
M&F
0-11 mos.*
104
208
312
416
Hispanic
M&F
1-2 yrs.
100
200
300
400
Hispanic
M&F
3-5 yrs.
100
200
300
400
Hispanic
M
6-11 yrs.
100
200
300
400
Hispanic
M
12-19 yrs.
102
204
306
408
Hispanic
M
20-39 yrs.
140
280
420
560
Hispanic
M
40-49 yrs.
70
140
210
280
Hispanic
M
50-59 yrs.
70
140
210
280
Hispanic
M
60+ yrs.
150
300
450
600
Hispanic
F
6-11 yrs.
100
200
300
400
Hispanic
F
12-19 yrs.
102
204
306
408
Hispanic
F
20-39 yrs.
140
280
420
560
Hispanic
F
40-49 yrs.
70
140
210
280
Hispanic
F
50-59 yrs.
70
140
210
280
Hispanic
F
60+ yrs.
147
294
441
588
Hispanic--Overall
1,565
3,130
4,695
6,260
Low Income White/Other
M&F
0-11 mos.*
45
90
135
180
Low Income White/Other
M&F
1-2 yrs.
54
108
162
216
Low Income White/Other
M&F
3-5 yrs.
54
108
162
216
Low Income White/Other
M
6-11 yrs.
27
54
81
108
Low Income White/Other
M
12-19 yrs.
27
54
81
108
Low Income White/Other
M
20-29 yrs.
31
62
93
124
Low Income White/Other
M
30-39 yrs.
31
62
93
124
Low Income White/Other
M
40-49 yrs.
31
62
93
124
Low Income White/Other
M
50-59 yrs.
31
62
93
124
Low Income White/Other
M
60-69 yrs.
31
62
93
124
Low Income White/Other
M
70-79 yrs.
31
62
93
124
Low Income White/Other
M
80+ yrs.
20
40
60
80
Low Income White/Other
F
6-11 yrs.
27
54
81
108
Low Income White/Other
F
12-19 yrs.
27
54
81
108
Low Income White/Other
F
20-29 yrs.
31
62
93
124
Low Income White/Other
F
30-39 yrs.
31
62
93
124
Low Income White/Other
F
40-49 yrs.
31
62
93
124
Low Income White/Other
F
50-59 yrs.
31
62
93
124
Low Income White/Other
F
60-69 yrs.
31
62
93
124
Low Income White/Other
F
70-79 yrs.
31
62
93
124
Low Income White/Other
F
80+ yrs.
31
62
93
124
Non-Low Income White/Other
M&F
0-11 mos.*
70
140
210
280
Non-Low Income White/Other
M&F
1-2 yrs.
70
140
210
280
Non-Low Income White/Other
M&F
3-5 yrs.
70
140
210
280
Non-Low Income White/Other
M
6-11 yrs.
70
140
210
280
Non-Low Income White/Other
M
12-19 yrs.
71
142
213
284
Non-Low Income White/Other
M
20-29 yrs.
79
158
237
316
Non-Low Income White/Other
M
30-39 yrs.
81
162
243
324
Non-Low Income White/Other
M
40-49 yrs.
82
164
246
328
Non-Low Income White/Other
M
50-59 yrs.
79
158
237
316
Non-Low Income White/Other
M
60-69 yrs.
80
160
240
320
Non-Low Income White/Other
M
70-79 yrs.
79
158
237
316
Non-Low Income White/Other
M
80+ yrs.
70
140
210
280
Non-Low Income White/Other
F
6-11 yrs.
70
140
210
280
Non-Low Income White/Other
F
12-19 yrs.
68
136
204
272
Non-Low Income White/Other
F
20-29 yrs.
75
150
225
300
Non-Low Income White/Other
F
30-39 yrs.
79
158
237
316
Non-Low Income White/Other
F
40-49 yrs.
79
158
237
316
Non-Low Income White/Other
F
50-59 yrs.
75
150
225
300
Non-Low Income White/Other
F
60-69 yrs.
72
144
216
288
Non-Low Income White/Other
F
70-79 yrs.
67
134
201
268
Non-Low Income White/Other
F
80+ yrs.
68
136
204
272
White/Other--Overall
2,238
4,476
6,714
8,952
Overall Total
5,000
10,000
15,000
20,000
*There are no explicit targets for infants (age <1 yr.). The numbers given here are the expected yield, given the estimated amount of screening.
Table 3. Expected NHANES sample size and response rates after four years (2007-2010) by sampling domains
Race/ethnicity-sex-age- income sampling domain
Projected population in year 2008
Total sample
Expected interview response rate (%)
Expected number of interviewed SPs
Expected exam response rate (%)
Expected number of examined SPs
Black, non-Hispanic
M&F
0-11 mos.
719,185
218
94%
205
92%
200
Black, non-Hispanic
M&F
1-2 yrs.
1,396,763
384
92%
352
88%
340
Black, non-Hispanic
M&F
3-5 yrs.
1,993,139
407
87%
356
84%
340
Black, non-Hispanic
M
6-11 yrs.
1,861,369
397
89%
352
86%
340
Black, non-Hispanic
M
12-15 yrs.
2,639,626
422
89%
375
87%
368
Black, non-Hispanic
M
16-19 yrs.
4,836,058
548
81%
445
77%
420
Black, non-Hispanic
M
20-39 yrs.
2,388,683
292
75%
219
72%
210
Black, non-Hispanic
M
40-59 yrs.
1,993,381
292
75%
219
72%
210
Black, non-Hispanic
M
60+ yrs.
1,833,520
684
67%
456
61%
420
Black, non-Hispanic
F
6-11 yrs.
1,812,239
402
88%
354
85%
340
Black, non-Hispanic
F
12-19 yrs.
2,650,667
388
90%
349
88%
340
Black, non-Hispanic
F
20-39 yrs.
5,771,249
533
81%
433
79%
420
Black, non-Hispanic
F
40-49 yrs.
2,914,677
283
77%
219
74%
210
Black, non-Hispanic
F
50-59 yrs.
2,434,324
283
77%
219
74%
210
Black, non-Hispanic
F
60+ yrs.
2,721,468
687
67%
459
61%
420
Black, non-Hispanic—Overall
37,966,348
6,220
81%
5,010
77%
4,788
Hispanic
M&F
0-11 mos.
956,023
456
95%
432
91%
416
Hispanic
M&F
1-2 yrs.
1,876,390
469
89%
419
85%
400
Hispanic
M&F
3-5 yrs.
2,719,343
461
92%
423
87%
400
Hispanic
M
6-11 yrs.
2,517,646
477
86%
410
84%
400
Hispanic
M
12-19 yrs.
3,239,835
466
90%
418
87%
408
Hispanic
M
20-39 yrs.
7,669,437
689
85%
587
81%
560
Hispanic
M
40-49 yrs.
2,959,450
359
81%
291
78%
280
Hispanic
M
50-59 yrs.
1,831,538
359
81%
291
78%
280
Hispanic
M
60+ yrs.
1,625,133
816
78%
633
74%
600
Hispanic
F
6-11 yrs.
2,422,751
467
87%
406
86%
400
Hispanic
F
12-15 yrs.
3,096,683
457
91%
416
89%
408
Hispanic
F
16-19 yrs.
7,083,806
690
84%
583
81%
560
Hispanic
F
20-39 yrs.
2,862,243
346
83%
286
81%
280
Hispanic
F
40-59 yrs.
1,921,269
346
83%
286
81%
280
Hispanic
F
60+ yrs.
2,083,573
814
75%
612
72%
588
Hispanic--Overall
44,865,120
7,671
85%
6,492
82%
6,260
Race/ethnicity-sex-age- income sampling domain
Projected population in year 2008
Total sample
Expected interview response rate (%)
Expected number of interviewed SPs
Expected exam response rate (%)
Expected number of examined SPs
Low-Income White/Other
M&F
0-11 mos.
456,475
196
93%
182
92%
180
Low-Income White/Other
M&F
1-2 yrs.
853,105
230
96%
220
94%
216
Low-Income White/Other
M&F
3-5 yrs.
1,247,951
235
94%
222
92%
216
Low-Income White/Other
M
6-11 yrs.
1,105,432
126
93%
117
86%
108
Low-Income White/Other
M
12-19 yrs.
1,559,851
125
87%
109
86%
108
Low-Income White/Other
M
20-29 yrs.
1,916,727
149
86%
129
83%
124
Low-Income White/Other
M
30-39 yrs.
1,253,152
171
75%
128
73%
124
Low-Income White/Other
M
40-49 yrs.
1,389,294
147
87%
128
84%
124
Low-Income White/Other
M
50-59 yrs.
1,245,643
161
80%
128
77%
124
Low-Income White/Other
M
60-69 yrs.
1,017,338
155
83%
128
80%
124
Low-Income White/Other
M
70-79 yrs.
642,642
180
74%
133
69%
124
Low-Income White/Other
M
80+ yrs.
436,802
131
75%
99
61%
80
Low-Income White/Other
F
6-11 yrs.
1,100,696
122
92%
112
89%
108
Low-Income White/Other
F
12-19 yrs.
1,537,174
119
91%
109
91%
108
Low-Income White/Other
F
20-29 yrs.
2,749,535
153
84%
128
81%
124
Low-Income White/Other
F
30-39 yrs.
1,705,231
144
88%
127
86%
124
Low-Income White/Other
F
40-49 yrs.
1,526,726
145
87%
127
86%
124
Low-Income White/Other
F
50-59 yrs.
1,485,365
152
88%
134
82%
124
Low-Income White/Other
F
60-69 yrs.
1,525,604
172
80%
138
72%
124
Low-Income White/Other
F
70-79 yrs.
1,339,664
180
71%
129
69%
124
Low-Income White/Other
F
80+ yrs.
1,466,528
227
76%
173
55%
124
Race/ethnicity-sex-age- income sampling domain
Projected population in year 2008
Total sample
Expected interview response rate (%)
Expected number of interviewed SPs
Expected exam response rate (%)
Expected number of examined SPs
Non-Low-Income White/Other
M&F
0-11 mos.
2,130,918
327
89%
292
86%
280
Non-Low-Income White/Other
M&F
1-2 yrs.
4,305,315
354
82%
289
79%
280
Non-Low-Income White/Other
M&F
3-5 yrs.
6,464,103
366
85%
310
76%
280
Non-Low-Income White/Other
M
6-11 yrs.
6,686,619
396
76%
302
71%
280
Non-Low-Income White/Other
M
12-19 yrs.
9,656,681
364
82%
299
78%
284
Non-Low-Income White/Other
M
20-29 yrs.
11,868,349
440
76%
333
72%
316
Non-Low-Income White/Other
M
30-39 yrs.
12,116,185
506
68%
345
64%
324
Non-Low-Income White/Other
M
40-49 yrs.
14,702,605
482
70%
336
68%
328
Non-Low-Income White/Other
M
50-59 yrs.
14,261,362
508
65%
329
62%
316
Non-Low-Income White/Other
M
60-69 yrs.
9,403,249
499
69%
345
64%
320
Non-Low-Income White/Other
M
70-79 yrs.
5,198,607
460
73%
337
69%
316
Non-Low-Income White/Other
M
80+ yrs.
2,813,405
462
69%
321
61%
280
Non-Low-Income White/Other
F
6-11 yrs.
6,314,206
360
82%
294
78%
280
Non-Low-Income White/Other
F
12-19 yrs.
9,186,595
342
81%
278
80%
272
Non-Low-Income White/Other
F
20-29 yrs.
11,181,398
406
78%
315
74%
300
Non-Low-Income White/Other
F
30-39 yrs.
11,997,292
453
73%
332
70%
316
Non-Low-Income White/Other
F
40-49 yrs.
14,954,947
461
72%
332
69%
316
Non-Low-Income White/Other
F
50-59 yrs.
14,638,075
441
71%
315
68%
300
Non-Low-Income White/Other
F
60-69 yrs.
9,840,533
449
68%
303
64%
288
Non-Low-Income White/Other
F
70-79 yrs.
5,931,088
490
61%
298
55%
268
Non-Low-Income White/Other
F
80+ yrs.
4,094,525
501
67%
337
54%
272
White/Other--Overall
215,306,993
12,487
76%
9,542
72%
8,952
TOTAL
298,138,462
26,378
80%
21,044
76%
20,000
Table 4. Expected distribution of NHANES sample for one year of data collection by sampling domains with 15 PSUs
Sex and Age
Total Examined Sample
Black, non-Hispanic
Hispanic
White/Other
Males and Females
Less than 1 year
269
50
104
115
1-2 years
309
85
100
124
3-5 years
309
85
100
124
Males
6-11 years
282
85
100
97
12-15 years
292
92
102
98
16-19 years
467
105
140
222
20-39 years
236
53
70
113
40-59 years
233
53
70
110
60-69 years
111
70-79 years
566
105
150
110
80+ years
90
Females
6-11 years
282
85
100
97
12-15 years
282
85
102
95
16-19 years
461
105
140
216
20-39 years
233
53
70
110
40-59 years
229
53
70
106
60-69 years
103
70-79 years
552
105
147
98
80+ years
99
Overall Total
5,000
1,197
1,565
2,238
Table 5: Minimum sample size* required in an analytic cell to estimate p with a CV of 30 percent by various design effects**
Proportions
p or (1-p)
Design effect
1
1.25
1.5
1.75
2
2.5
3
0.01
1,100
1,375
1,650
1,925
2,200
2,750
3,300
0.02
544
681
817
953
1,089
1,361
1,633
0.05
211
264
317
369
422
528
633
0.10
100
125
150
175
200
250
300
0.15
63
79
94
110
126
157
189
0.20
44
56
67
78
89
111
133
0.25
33
42
50
58
67
83
100
0.30
30
38
45
53
60
75
90
0.40
30
38
45
53
60
75
90
0.50
30
38
45
53
60
75
90
*Sample size n= deff* (1‑p)/( p* CV**2) for p<=0.25; n= 30 * deff for p>0.25
**deff=1 for SRS
Table 6: Minimum sample size* required in an analytic cell to estimate difference in p with a CV of 30 percent by various design effects**
Estimated proportions
Design Effect
p1
p2
1
1.25
1.5
1.75
2
2.5
3
0.05
0.10
611
764
917
1,069
1,222
1,528
1,833
0.05
0.15
194
243
292
340
389
486
583
0.05
0.20
102
128
154
179
205
256
307
0.10
0.15
967
1,208
1,450
1,692
1,933
2,417
2,900
0.10
0.20
278
347
417
486
556
694
833
0.10
0.25
137
171
206
240
274
343
411
0.15
0.20
1,278
1,597
1,917
2,236
2,556
3,194
3,833
0.15
0.25
350
438
525
613
700
875
1,050
0.15
0.30
167
208
250
292
333
417
500
0.20
0.25
1,544
1,931
2,317
2,703
3,089
3,861
4,633
0.20
0.30
411
514
617
719
822
1,028
1,233
0.20
0.35
191
239
287
335
383
478
574
0.25
0.30
1,767
2,208
2,650
3,092
3,533
4,417
5,300
0.25
0.35
461
576
692
807
922
1,153
1,383
0.25
0.40
211
264
317
369
422
528
633
0.30
0.35
1,944
2,431
2,917
3,403
3,889
4,861
5,833
0.30
0.40
500
625
750
875
1,000
1,250
1,500
0.30
0.45
226
282
339
395
452
565
678
0.40
0.45
2,167
2,708
3,250
3,792
4,333
5,417
6,500
0.40
0.50
544
681
817
953
1,089
1,361
1,633
0.40
0.55
241
301
361
421
481
602
722
0.50
0.55
2,211
2,764
3,317
3,869
4,422
5,528
6,633
0.50
0.60
544
681
817
953
1,089
1,361
1,633
0.50
0.65
236
295
354
413
472
590
707
*n=deff*(p1*q1 +p2*q2)/((CV*(p1‑p2))**2); q=1-p;
**deff=1 for SRS
Table 7a. NHANES examined sample (n=10,000) after two years. Estimated CVs for a 10-percent statistic, assuming a design effect of 1.5
NOTES:
Sex and Age
Total Examined Sample
Black, non-Hispanic
Hispanic
White/Other
Males and Females
Less than 1 year
0.158
0.367
0.255
0.242
1-2 years
0.148
0.282
0.260
0.233
3-5 years
0.148
0.282
0.260
0.233
Males
6-11 years
0.155
0.282
0.260
0.264
12-19 years
0.152
0.271
0.257
0.262
20-39 years
0.120
0.254
0.220
0.174
40-49 years
0.169
0.359
0.311
0.244
50-59 years
0.170
0.359
0.311
0.248
60-69 years
0.247
70-79 years
0.109
0.254
0.212
0.248
80+ years
0.274
Females
6-11 years
0.155
0.282
0.260
0.264
12-19 years
0.155
0.282
0.257
0.267
20-39 years
0.121
0.254
0.220
0.177
40-49 years
0.170
0.359
0.311
0.248
50-59 years
0.172
0.359
0.311
0.252
60-69 years
0.256
70-79 years
0.111
0.254
0.214
0.262
80+ years
0.261
Overall Total
0.037
0.075
0.066
0.055
Table 8a. NHANES examined sample (n=10,000) after two years. Estimated CVs for a 5-percent statistic, assuming a design effect of 1.5
NOTES:
Sex and Age
Total Examined Sample
Black, non-Hispanic
Hispanic
White/Other
Males and Females
Less than 1 year
0.230
0.534
0.370
0.352
1-2 years
0.215
0.409
0.377
0.339
3-5 years
0.215
0.409
0.377
0.339
Males
6-11 years
0.225
0.409
0.377
0.383
12-19 years
0.221
0.394
0.374
0.381
20-39 years
0.175
0.368
0.319
0.253
40-49 years
0.246
0.521
0.451
0.355
50-59 years
0.248
0.521
0.451
0.360
60-69 years
0.358
70-79 years
0.159
0.368
0.308
0.360
80+ years
0.398
Females
6-11 years
0.225
0.409
0.377
0.383
12-19 years
0.225
0.409
0.374
0.387
20-39 years
0.176
0.368
0.319
0.257
40-49 years
0.248
0.521
0.451
0.360
50-59 years
0.250
0.521
0.451
0.367
60-69 years
0.372
70-79 years
0.161
0.368
0.311
0.381
80+ years
0.379
Overall Total
0.053
0.109
0.095
0.080
Table 7b. NHANES examined sample (n=20,000) after four years. Estimated CVs for a 10-percent statistic, assuming a design effect of 1.5
NOTES:
Sex and Age
Total Examined Sample
Black, non-Hispanic
Hispanic
White/Other
Males and Females
Less than 1 year
0.112
0.260
0.180
0.171
1-2 years
0.105
0.199
0.184
0.165
3-5 years
0.105
0.199
0.184
0.165
Males
6-11 years
0.109
0.199
0.184
0.187
12-19 years
0.108
0.192
0.182
0.186
20-39 years
0.085
0.179
0.155
0.123
40-49 years
0.120
0.254
0.220
0.173
50-59 years
0.120
0.254
0.220
0.175
60-69 years
0.174
70-79 years
0.077
0.179
0.150
0.175
80+ years
0.194
Females
6-11 years
0.109
0.199
0.184
0.187
12-19 years
0.109
0.199
0.182
0.188
20-39 years
0.086
0.179
0.155
0.125
40-49 years
0.120
0.254
0.220
0.175
50-59 years
0.122
0.254
0.220
0.178
60-69 years
0.181
70-79 years
0.078
0.179
0.152
0.186
80+ years
0.185
Overall Total
0.026
0.053
0.046
0.039
Table 8b. NHANES examined sample (n=20,000) after four years. Estimated CVs for a 5-percent statistic, assuming a design effect of 1.5
NOTES:
Sex and Age
Total Examined Sample
Black, non-Hispanic
Hispanic
White/Other
Males and Females
Less than 1 year
0.163
0.377
0.262
0.249
1-2 years
0.152
0.290
0.267
0.240
3-5 years
0.152
0.290
0.267
0.240
Males
6-11 years
0.159
0.290
0.267
0.271
12-19 years
0.156
0.278
0.264
0.270
20-39 years
0.124
0.260
0.226
0.179
40-49 years
0.174
0.368
0.319
0.251
50-59 years
0.175
0.368
0.319
0.255
60-69 years
0.253
70-79 years
0.112
0.260
0.218
0.255
80+ years
0.281
Females
6-11 years
0.159
0.290
0.267
0.271
12-19 years
0.159
0.290
0.264
0.274
20-39 years
0.124
0.260
0.226
0.182
40-49 years
0.175
0.368
0.319
0.255
50-59 years
0.177
0.368
0.319
0.259
60-69 years
0.263
70-79 years
0.114
0.260
0.220
0.270
80+ years
0.268
Overall Total
0.038
0.077
0.067
0.056
B. NHANES Analytic and Reporting Guidelines (available online at http://www.cdc.gov/nchs/about/major/nhanes/nhanes2003-2004/analytical_guidelines.htm)
Last Update: December, 2005
Last Correction: September, 2006
Introduction
This document presents analytic and reporting guidelines that should be used for NHANES data analyses and publications. It represents the latest information from the National Center for Health Statistics on recommended approaches for analysis of all NHANES data, but with a particular focus on data collected in the continuous NHANES (since 1999). Previous versions of NHANES analytic guidelines (the NHANES III Analytic Guidelines http://www.cdc.gov/nchs/about/major/nhanes/nhanes3/nh3gui.pdf and the NHANES 1999-2000 Addendum to the NHANES III Analytic Guidelines http://www.cdc.gov/nchs/data/nhanes/guidelines1.pdf) can still be used. These analytic guidelines will be modified and updated on a periodic basis as new information is acquired and as new statistical techniques for analysis of complex sample surveys are introduced. Users should regularly visit the NHANES website to see if a new version of these latest analytic guidelines has been released.
Summary recommendations
Following is the current list of analytic and reporting guidelines for NHANES public release data. Additional guidelines may be included on future updates as well as more detailed information and examples for some of the existing guidelines.
1. The first and over-riding analytic guideline is that the data user, prior to any analysis of the data, should read all relevant documentation for the survey and for the specific data items to be used in an analysis.
Many analytic problems and misinterpretation of the data can be avoided by reading the documentation, examining the data collection protocols and data collection instruments, and conducting preliminary descriptive evaluation of the data. The documentation will indicate how the data were collected, how the data are coded and the amount of missing data. The documentation will also indicate if a data item was collected on all or a sub-sample of sample persons, if it was collected on a limited age-range, or if exclusion criteria were applied for a specific examination component. Specific information on laboratory tests and quality control for these tests are available. For trend analysis, the current documentation can be compared with documentation from past NHANES surveys to determine if a specific data item is comparable with a similar data item collected in previous surveys.
Data collected in NHANES comes from interviews, examinations, and laboratory tests based on blood and urine samples. There may also be measures taken in the home, such as dust or tap water collection. The source of a data item (interview, MEC, sera) is important for both assessment of quality of information and for determining the appropriate sampling weight to be used for producing statistical estimates.
As with any data set, NHANES data are subject to sampling and non-sampling
errors (including measurement error). Interview (questionnaire) data are based on self-reports and are therefore subject to non-sampling errors such as recall problems, misunderstanding of the question, and a variety of other factors. Examination data and laboratory data are subject to measurement variation and possible examiner effects. The NHANES program maintains high standards to insure non-sampling and measurement errors are minimized. Prior to data collection, extensive protocols are developed and reviewed by the public health and scientific community. Prior to and during data collection, NHANES field staff participate in comprehensive training and annual refresher training for Interviewers and MEC staff. As data are processed, extensive quality control procedures are applied. Despite the rigorous quality control standards, estimates produced from any data set are subject to sampling and non-sampling variation and interpretation of analysis must proceed accordingly.
Data content and data collection protocols may change over time; this is another reason to read the documentation in order to understand any issues in comparability of data over time. Changes in methods may occur at any time and the user should not assume they have
2. NHANES has changed from a periodic survey to a continuous survey and the release of public use data files (and their format) has changed as well.
In the past, NHANES surveys were conducted on a periodic basis and the data were released as single, multiyear data sets. For example, NHANES III covered the 6 calendar years 1988-1994 and is generally analyzed as one, 6-year survey. In addition, previous NHANES public use data files tended to be large and few in number. Since 1999, NHANES has been planned and conducted as a continuous annual survey. For a variety of reasons, including disclosure issues, the continuous NHANES survey data is released on public use data files in two-year increments (e.g. NHANES 1999-2000, NHANES 2001-2002, NHANES 2003-2004, etc.). Since the inception of the continuous NHANES, public use data files are released on an ongoing basis as many smaller component-specific data files. For a two-year analysis, sample size is smaller and the number of geographic units in the sample is more limited than, for example NHANES III. Sample size and statistical power consideration should be used to determine if a two-year sample is sufficient for a particular analysis or if 4 (or even 6) years of the survey need to be combined to produce statistically reliable analysis. This is addressed more fully later in this document.
3. Be aware of the complex survey design and sample weighting methodology..
NHANES is a complex sample survey. The overall sample design and weighting methodology has been similar over the history of the survey. The sample design and weighting methodology for NHANES 1999-2004 is very similar to past NHANES data releases. Primary Sampling Units (PSUs) are generally single counties, although small counties are sometimes combined to meet a minimum population size. In the years 1999-2001, NHANES was based on a design linked to the National Health Interview Survey (NHIS). The NHANES PSUs were a subset of the PSUs previously selected for the NHIS. An independent set of PSU’s was selected for 2002-2006; the sampling frame for this design was all counties in the United States.
The additional stages of selection in the probability design for NHANES 1999-2004 remain very similar to past NHANES designs. Clusters of households are selected and each person in a selected household is screened for demographic characteristics. One or more persons per household may be selected for the sample. For NHANES 1999-2000, there were 12,160 persons selected for the sample, 9,965 of those were interviewed (81.9 percent) and 9,282 (76.3 percent) were examined in the MEC. For NHANES 2001-2002, there were 13,156 persons selected for the sample, 11,039 of those were interviewed (83.9 percent), and 10,477 (79.6 percent) were examined in the MEC. For NHANES 2003-2004, there were 12,761 persons selected for the sample, 10,122 of those were interviewed (79.3 percent) and 9,643 (75.6 percent) were examined in the MEC.
As with any complex probability sample, the sample design information should be explicitly used when producing statistical estimates or undertaking statistical analysis of the NHANES data. In particular, sample weights and the first stage of the cluster design need to be considered. The sampling weights provided must be used to produce unbiased national estimates. The sample weights for NHANES 2003-2004 reflect the unequal probabilities of selection, non-response adjustments and adjustments to independent population controls. The proper sample weight must be used. If only data from the Interviewed sample is used, then the appropriate SAS variable is WTINT2YR. If data from the MEC examination is used, then the appropriate SAS variable is WTMEC2YR.
Because NHANES is a complex probability sample, analytic approaches based on data from simple random sample are usually inappropriate. Ignoring the complex design can lead to biased estimates and overstated significance levels. Sample weights and the stratification and clustering of the design must be incorporated into an analysis to get proper estimates and standard errors of estimates.
Data are sometimes collected on sub-samples of the full design for any NHANES survey. These data are available but public release of these files may lag behind the main data release for any two-year period due to extra time needed for processing and quality assurance review. In addition, each subsample involves another stage of selection and separate sample weights that account for that stage of selection and additional non-response. For analysis of subsample data, appropriate subsample weights must be used and they are included on any data file where relevant.
4. Be aware of, and utilize, proper variance estimation procedures.
The procedure for variance estimation (sampling errors) is the same for 2003-2004 as for 2001-2002. This method creates Masked Variance Units (MVUs) which can be used as if they were stratified PSU’s to estimate sampling errors (similar to past NHANES). The MVUs on the NHANES demographic data files are not the “true” design PSUs. They are a collection of secondary sampling units that are aggregated into groups called Masked Variance Units for the purpose of variance estimation. The MVUs produce variance estimates that closely approximate the variances that would have been estimated using the “true” design structure. These MVUs have been created for each two-year cycle of NHANES and can be used for any combination of two-year data cycles without recoding by the user.
For NHANES 2001-2002 and 2003-2004, the two-year weights and MVUs are included in the Demographics data file. The NHANES1999-2000 Demographic file was updated to include MVU’s and four-year sample weights. Only the NHANES 1999-2002 data have special four year sample weights (as described in the NHANES Analytic Guidelines section on how and when to combine years of data). At this time, the preferred approach for calculating sampling errors is to use the MVUs and to ignore the JK-1 technique that served as an interim approach for variance estimation when the NHANES 1999-2000 data were released.
The stratum variable is SDMVSTRA and the PSU variable is SDMVPSU. Software specific for survey data, such as SUDAAN, or software that has specific survey procedures, such as STATA and SAS, can be used to estimate sampling errors by the Taylor series (linearization) method. Typically, the data set should first be sorted by SDMVSTRA and SDMVPSU. For NHANES 1999-2000, SDMVSTRA is numbered 1-13; for NHANES 2001-2002, SDMVSTRA is numbered 14-28; and for NHANES 2003-2004 SDMVSTRA is numbered 29-43. Therefore, these files can be combined without any recoding of this variable. This procedure will also hold for combining NHANES 2001-2002 and 2003-2004 data files, as well as future two-year NHANES files. There are no replicate weights provided for NHANES 2003-2004. Replication techniques can still be used to estimate sampling errors if the software, such as WESVAR, computes its own set of replicate weights based on the nested MVU/PSU within stratum design.
Variance estimates for NHANES I, NHANES II, HHANES, and NHANES III utilized the true design PSUs. Pseudo strata and pseudo PSU variables were included on each public use data file for those surveys and the same software can be used to estimate sampling errors for each of those surveys.
5. Combining two or more 2-year cycles of the continuous NHANES is encouraged and strongly recommended in order to produce estimates with greater statistical reliability for demographic sub-domains and rare events,.
For two-year cycles, the sample size may be too small to produce statistically reliable estimates for very detailed demographic sub-domains (e.g. sex-age-race/ethnicity groups) or for relatively rare events. The sample design for NHANES makes it possible to combine two or more “cycles” to increase the sample size and analytic options. Each two-year cycle and any combination of those two years cycles is a nationally representative sample.
When combining cycles of data, it is extremely important that (1) the user verify that data items collected in all combined years were comparable in wording and methods and (2) use a proper sampling weight. Beginning in 2003, the survey content for each two year period is held as constant as possible to be consistent with the data release cycle. In the first four years of the continuous survey, this was not always the case, and some special data release and data access procedures had to be developed and used for selected survey content collected in “other than two-year” intervals (http://www.cdc.gov/nchs/data/nhanes/nhanes_release_policy.pdf) .
6. The decision on how many years of NHANES data are required for a particular analysis can be summarized by the concept of minimum sample size required.
The minimum sample size is determined by the statistic to be estimated (e.g. mean, total, proportion…), the reliability criteria (e.g. 20 or 30 percent relative standard error), the Design Effect for the statistics (DEFF defined as the variance inflation factor), and the degrees of freedom for the standard error estimate. For example, consider the minimum sample size to estimate a10 percent prevalence with relative standard error 30 percent or less, a survey DEFF of 1.5, and greater than 16 degrees of freedom for the standard error. The required minimum sample size is 150. Now consider the following simplified example (not real data).
Table1. Sample Size by Data Cycle and Sub-domain
1999-2000
2001-2002
2003-2004
Combined 4 years
Combined 6 years
Total
210
210
210
420
630
Males
110
110
110
220
330
age < 40
60
60
60
120
180
age > 40
50
50
50
100
150
Females
100
100
100
200
300
In this example, one could estimate the proportion for the total population in each of the 2-year data cycles but none of the sub-domains meets the minimum sample size requirement. Combining the data from two cycles to produce a 4 year dataset (in this case, a 1999-2002 or a 2001-2004 dataset) allows the proportion to be reliably estimated for both males and females. For a more detailed domain however such as Males less than 40 years of age, 6 years of data are required.
Earlier NHANES surveys were conducted for four or more years and, thus, have larger samples than the two-year cycles of the continuous NHANES. However, in each of the NHANES conducted prior to 1999, many sub-domains did not meet minimum sample size requirements and in those cases, the above concerns were (and still are) relevant.
7. When combining two or more two-year cycles of continuous NHANES data, the user should use the following procedure for calculating the appropriate combined sample weights.
When two or more 2-year cycles of the continuous NHANES are combined, the user must calculate new sample weights before analyzing the data. NCHS does not calculate sample and release all possible combinations of multiple two-year cycles of the continuous survey because it would be impractical to produce them and include them on all public release files.
The sample weights for NHANES 1999-2000 were based on population estimates developed by the Bureau of the Census before the Year 2000 Decennial Census counts became available. The two-year sample weights for NHANES 2001-2002 were based on population estimates that incorporate the year 2000 Census counts. The two population estimates were not strictly comparable. Therefore, appropriate four-year sample weights (comparable to Census 2000 counts) were calculated and added to the demographic data files for both 1999-2000 and 2001-2002. The four-year sample weights have the same variable name in each file. For example, the four-year examination sample weight in both files is WTMEC4YR. Thus, users of the earlier release of the NHANES 1999-2000 demographic file must use the updated demographic file to appropriately analyze the combined four-year data 1999-2002. Because NHANES 2003-2004 uses the same year 2000 Census counts as were used for NHANES 2001-2002, there is no need to create special four-year weights for 2001-2004.
For a four year estimate for 2001-2004, one can create a new variable for a four year weight by assigning ½ of the 2 year weight for 2001-2002 if the person was sampled in 2001-2002 or assigning ½ of the 2 year weight for 2003-2004 if the person was sampled in 2003-2004. This is possible because the 2 year weights for 2003-2004 are comparable to the 2001-2002 weights (in terms of a population basis). For an estimate for the 6-years 1999-2004, a 6-year weight variable can be created by assigning 2/3 of the 4 year weight for 1999-2002 if the person was sampled in 1999-2002 or assigning 1/3 of the 2 year weight for 2003-2004 if the person was sampled in 2003-04. This is possible because the 2003-2004 weights are also comparable (on a population basis) to the combined four-year weights specifically created for 1999-2002.
Summary comments and future additions to the NHANES Analytic Guidelines.
This document summarizes the most recent analytic and reporting guidelines that should be used for most NHANES analyses and publications. It is important for users to understand the entire document and to become familiar with statistical issues in the analysis of complex survey data.
These suggested guidelines provide a framework to users for producing estimates that conform to the analytic design of the survey. Because statistical methods for analyzing complex survey data are continually evolving, these recommendations may differ slightly from those used by analysts for previous NHANES surveys.
It is important to remember that the statistical guidelines in this document are not absolute. When conducting analyses, the analyst needs to use his/her subject matter knowledge (including methodological issues), as well as information about the survey design. The more one deviates from the original analytic categories and original analytic objectives defined in the planning documents, the more important it is to evaluate the results carefully and to interpret the findings cautiously.
Future versions of this NHANES Analytic and Reporting Guidelines will include additional topics, such as sample sizes and response rates for each NHANES survey, hypothesis testing, multivariate analysis, and a discussion of the concept of statistical versus practical significance.
These are guidelines not standards. Depending upon the subject matter and statistical efficiency, specific analyses may depart from these guidelines. The burden of proof for statistical efficiency and for appropriate data interpretation is on the data analyst.
One final reminder for NHANES data users is that the NHANES data files, documentation, and Analytic Guidelines may be edited and/or updated to reflect new information and corrected or edited data. NHANES data users are encouraged to check the NHANES website periodically (available at: http://www.cdc.gov/nchs/about/major/nhanes/NHANES99_00.htm) to determine if new or revised data files and analytic guidelines have been released by NCHS for the data of interest. Data users are encouraged to subscribe to the NHANES listerv (available at: http://www.cdc.gov/nchs/about/major/nhanes/nhaneslist.htm) to receive information updates.