2005 Census Survey of MaricopaHousehold Survey

Sample Design Overview

Sample Size Assumptions

Sample Design Overview

1. Calculate sample size2. Select a sample of blocks in each jurisdiction

- assign blocks to each jurisdiction- virtually all blocks in sample in small

jurisdictions- larger jurisdictions: all large blocks

in sample & a subsample of small blocks

3. Create list of HU addresses in sample blocks- lister given current address list- add HU addresses not on current list- delete HU addresses on current list that are no longer in block- initial listing in May-July 2005- supplemental list updating in Aug. 2005

4. Select a sample of HU addresses from listing

Sample Size Assumptions

1. Desired accuracy

- 95% confidence interval= +/- 2%

- one standard error = 1%

- see handout for an illustration of the 95% confidence interval expected for your jurisdiction

2. Vacancy rate- the higher the vacancy rate the larger the sample size needs to be- 2000 census vacancy rates used- if 2005 rate smaller, smaller sample needed- if 2005 rate higher, larger sample needed- let Heidi know if you expect the 2005 vacancy rate will be different than the2000 vacancy rate shown in table 3 of the minutes of the 9/21/2004 POPTAC meeting

-the effect of this change in vacancy rates should not have a substantial impact on the sample size -for example, if a jurisdiction needed a sample size of about 3000 using a 10% vacancy rate from 2000 and the 2005 vacancy rate is expected to be 5% then the sample size could be lowered to 2850. Likewise, a 10 % vacancy rate raised to 20% in 2005 would require the sample size to be increased to 3375.

3. Variability in household size-the more the variation in household size the larger the sample size needs to be- 2000 census variability used- if 2005 less variable, smaller sample size - if 2005 more variable, larger sample size- let Heidi know if you expect the 2005 persons per household will be different than the 2000 persons per household shown in Table 3 of the minutes of the 9/21/2004 POPTAC meeting

- the effect of this change in persons per HH will be most substantial in jurisdictions with:

- a large relative increase since 2000 - the size of the new HHs expected to be a lot different than the current HH size

- for example a jurisdiction with - an average HH size of 3.0- an expected 50% growth in HHs- new HHs mostly senior HHs with 1 or 2 This jurisdiction would probably require a significant increase in sample size due to the increase in HH size variability.

4. Proportion of total HUs in sample - the higher the % in sample the smaller the sample size needs to be- for example, consider a jurisdiction of 100,000 HUs that requires a sample size of 4750 to achieve the 2% accuracy. - if that jurisdiction was only 5,000 HUs, it would require a sample size of only 2500 - if it was 10,000 HUs, sample size = 3300 - if it was 50,000 HUs, sample size = 4500

5. Household survey response rate- 100% response rate assumed

- 95 % confidence interval error will increase by about the nonresponse rate

- 5% nonresponse rate means 95% CI error = +/- 2.05% rather than 2.0%

- 10% nonresponse rate means 95% CI error = +/- 2.1% rather than 2.0%