|October 29th, 2016|
One issue, though, is it could be that the cheapest apartments are listed only on Craigslist  and not on the other services that Padmapper pulls from. To get a rough check this, I took ten random listings from the Boston Craigslist page, and tried to figure out which Padmapper listing it went with.
2br at 300 2nd Ave Needham for $3697. In Padmapper. My map doesn't go this far out.
2br on Crawford St in Watertown for $1700. Not in Padmapper. My map predicts $2065.
1br near Broadway at Oxford St in Arlington for $1495. Not in Padmapper. My map predicts $1775.
2br on Harvey St in Cambridge for $2900. In Padmapper. My map predicts $2800.
Studio at 1110 Comm Ave in Allston for $1575. In Padmapper. My map predicts $1590.
3br on Tremont St in Cambridge for $3000. Not in Padmapper. My map predicts $2995.
3br on Bromfield Rd in Somerville for $3000. In Padmapper. My map predicts $3155.
3br in Cambridge for $6000. Not in Padmapper. This listing is kind of nuts, since it gives no pictures or address information beyond just "Cambridge". Even for Harvard Sq my map only predicts $3650.
2br on Somerville Ave in Somerville for $1700: Not in Padmapper. My map predicts $2605.
2br on 400 Foxborough Blvd in Foxboro for $2215. In Padmapper. My map doesn't go this far out.
Fixing this is pretty tricky. I could do a larger sample to try to get a better sense of what the error is, and then adust my map down by the combination of how much lower the non-Padmapper apartments are and what fraction aren't in padmapper. In this case, ignoring the dubious listing, 4 of 9 weren't on padmapper, with an average error of 23%, that would mean adjusting all my estimates down by 10%. On the other hand, as people's listing behavior changes this could get obsolete pretty quickly, and it's a pain to calculate the first time let alone on an ongoing basis. Ideas?
 Or, worse for my map, listed only with signs in windows or something else not available online.