Assignment 3 - Sampling Exercise

1. Calculate the actual median household income for Northridge using all the census tracts provided herein (see below for list). You would accomplish this by determining the proportion of households that each census tract bears to the total households. This proportion is then placed in an additional column labeled "WT"and multiplied by the median household income in that census tract. These results would be placed in the column marked "WT x HH$". Adding this column gives the ACTUAL weighted median household income for Northridge.

2. Now number the census tracts and choose four at random using a table of random numbers (i.e. numbers from 01 to 19 in the table), highlighting the choices. Determine the proportion that the households in those four tracts bear to the total of the four census tracts. Place those weights in separate column. Multiple those weights times their respective median household income. Add these numbers to get the SIMPLE RANDOM SAMPLE ESTIMATE of the weighted median household income. Compare this result to the population income found in #1 above. What is the difference (error)?

3. Divide Northridge into four income "strata" starting at $20-39,999 and incrementing at $20,000 intervals with the last interval $80,000 and above. Sort the Census tracts by income, low to high. Place each census tract into one of the four income intervals, by drawing a line at the appropriate "breaks" corresponding to the income intervals. From each strata, choose one at random (i.e. number each strata 01-?? and use a table of random numbers to choose one from each segment). Determine what proportion its housing units represents of the total number of housing units for the four sample census tract chosen one from each strata. Calculate the weighted median for the four census tracts in the same manner as in #2 above. Add the resulting weighted incomes to get the STRATIFIED RANDOM SAMPLE ESTIMATE of household income for Northridge. How does this compare to the actual income in #1. .

WHICH IS MORE ACCURATE??