2005 Census Survey of Maricopa Household Survey Sample Design Overview Sample Size Assumptions

Sample Design Overview 1. Calculate sample size 2. 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 supplemental list updating in Aug 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 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 the 2000 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 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 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 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 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 if it was 10,000 HUs, sample size = 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%