Brigitte Roth Tran

Who they are

This page records the public professional record only. Nothing adverse is recorded and no motive is attributed.

She is described in the letter as a senior economist in the Economic Research Department of the Federal Reserve Bank of San Francisco. Her wider career was not verified for this page, so none is asserted here. The record used is one letter, read in full.

Key papers

Roth Tran, B. (2022), 'The Impact of Weather on Retail Sales', FRBSF Economic Letter 2022-23, Federal Reserve Bank of San Francisco, 22 August 2022. Read in full.

Her wider publication record was not surveyed for this page.

Key ideas

The data are daily store-level sales from more than 100 United States stores of a national apparel and sporting goods brand, April 2010 to December 2013, matched to weather station data. Stores are classed as indoor or outdoor according to whether shoppers can move between stores without exposure to the weather. Weather is summarised as an index scaled so that higher values mean more favourable weather for sales.

The findings are four. Online sales did not offset bad-weather store losses, and on good-weather days online sales rose. Only a small share of the store response was offset by shoppers moving between indoor and outdoor centres. Good-weather gains were offset by lower sales in the following weeks and were no longer statistically significant by four weeks, while bad-weather losses persisted: a moderately bad day cost a net quarter of a day's sales and a very bad day an average of about 40 per cent, excluding days when stores closed. Stores with more experience of a kind of weather responded less to it.

That asymmetry is the working example of demand displacement on this site, and it is the basis for the planning rule offered, with its limit, in What a Weather Forecast Does for Sales.

The letter makes no formal forecasts and does not discuss seasonal adjustment. It covers one brand's stores, and its online estimates apply to local sales, not aggregate sales. Its author concludes that adaptation could make the impact of more severe weather smaller than current responses suggest, but that weather arriving in areas with little experience could make current average responses understate the disruption.

How to read the result

The letter earns its place in the article by being specific. It uses daily sales at more than 100 stores of one national apparel and sporting goods brand, April 2010 to December 2013, matched to weather station data, and it builds an index in which higher values mean more favourable weather for sales. Stores are classed as indoor or outdoor by whether shoppers can move between shops without exposure to the weather, which lets the letter test whether shoppers simply went elsewhere.

The two-sided result is the useful part. On the good side, gains were offset by lower sales in the following weeks and were no longer statistically significant by four weeks. On the bad side, losses persisted: a moderately bad day cost a net quarter of a day's sales, and a very bad day about 40 per cent on average, with closure days excluded. A planner who reads only the second half will overstate the case for cutting orders, and one who reads only the first will overstate the case for ordering more after a fine weekend.

The adaptation finding deserves attention too. Stores in places with more experience of a kind of weather lost less to it: for precipitation over two inches, the average sales decline was about 80 per cent smaller where experience was above the median. The author concludes that adaptation could make future impacts smaller than current responses suggest, while weather arriving in places with little experience could make them larger. A model fitted in one climate should not be moved to another unexamined.

What the record does not show

The letter makes no formal forecasts and does not discuss seasonal adjustment. It covers one brand, and its online estimates apply to local sales, not to aggregate sales, so it cannot say what happens to an online retailer's total. The result that online sales rose on good-weather days sits beside Sebastian Steinker's opposite sign for a European fashion retailer, and the record cannot settle why. Her position at the Federal Reserve Bank of San Francisco is taken from the letter's byline.

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