The latest estimates from IHP’s SLOTS MRP model (revised 01/2024) show the SJB (+1) and NPP/JVP (-3) both having 34% support of Sri Lankan adults in April. Support for NPP/JVP and SJB has shown a modest increasing trend since July 2023.  Voters' support for UNP, SLPP, SLFP, ITAK, SLMC and “Others” parties remain relatively unchanged. The April estimates are provisional and are associated with a margin of error of 1–4% for the four leading parties. 

Compared to IHP’s April release, IHP estimates of NPP/JVP and SJB support in Mar. 2024 were revised +2 and -5 points respectively. 

Dr. Rannan-Eliya, the SLOTS polling director, commented: “The SLOTS polling in April suffered from a lower response rate owing to the New Year holidays, and we think this may have skewed the sample in favour of SJB supporters. The early May interviews partly compensated for this, and it’s possible that our June interviews may result in further revisions to our model estimates.”

Dr. Rannan-Eliya also commented: “We’ve been asked about some other recent internet polls that showed much higher levels of support for the NPP/JVP. We think these over-estimate NPP/JVP support. SLOTS routinely collects data from all respondents on whether they have internet access, and whether they are willing to participate in an internet survey. These data show that NPP/JVP supporters are far more likely to have internet access and even more likely to be willing to respond to internet surveys, and this difference remains even after controlling for past voting behaviour. Our data indicates internet polls may overestimate NPP/JVP support by about 10%, and for this kind of reason we have previously decided that the time is not right to do internet polling.”

These SLOTS estimates are for all adults and not for likely voters. They are based on the 01/ 2024 revision of the IHP SLOTS Multilevel Regression and Poststratification (MRP) model. IHP is working on improving its likely voter model and will resume release of voting intent in likely voters in a future update. But it should be noted that differences in voting intent shares between all adults and likely voters have typically been 1–2% for most estimates in the past two years.

This April 2024 update is based on 17,134 interviews conducted with adults across Sri Lanka since Oct. 2021, including 444 interviews carried out in Apr. 2024. IHP’s SLOTS MRP methodology first estimates the relationship between a wide variety of characteristics about respondents and their opinions – in this case, ‘If there was a General Election today, which party would you vote for?’– in a multilevel statistical model. It then uses a large data file that is calibrated to the national population to predict voting intent in each month since Oct. 2021, according to what the multilevel model says about their probability of voting for various parties (‘post-stratification’) at each point in time. The multilevel model was estimated 100 times to reflect underlying uncertainties in the model and to obtain margins of error.

About IHP

IHP is an independent, non-partisan research centre based in Colombo, Sri Lanka. The SLOTS lead investigator is Dr Ravi Rannan-Eliya of IHP, who has trained in public opinion polling at Harvard University and has conducted numerous surveys over three decades. 

Methodology details

SLOTS combines interviews from a national sample of adults (ages 18 and over) reached by random digit dialling of mobile numbers, and others coming from a national panel of respondents who were previously recruited through random selection and face-to-face interviews. IHP estimates voting intent using an adaptation of Multilevel Regression and Post-Stratification (MRP), with multiple imputations to account for uncertainties in its modelling, exploiting data from all SLOTS interviews to estimate voting in a particular month. 

The April 2024 MRP estimates are based on 17,134 interviews conducted from 1 October 2021–19 May 2024, including 444 interviews conducted in April 2024. The margin of error is assessed as 0.7–1.8% for the UNP, SLPP, SLFP, SLMC, CWC, ITAK and the “other” parties, and 3.7–4.0% for NPP/JVP and SJB. A total of 100 bootstraps were used to estimate margins of error.

MRP is a method that is increasingly used by polling firms in other countries to leverage small samples, most notably by YouGov which used it to forecast results of the UK Brexit Referendum and recent UK general elections. All estimates are adjusted to ensure the sample matches the national population with respect to age, sex, ethnicity, socioeconomic status, education, geographical location, and voting in the 2019 Presidential and 2020 General Elections.

Funding

The SLOTS survey has previously been funded by the Neelan Tiruchelvam Trust, the UK National Institute for Health and Care Research (NIHR), The Asia Foundation in Sri Lanka, and others. Current fieldwork is financed by the IHP Public Interest Research Fund and others. The sponsors play no role in the study design, analysis, or interpretation of findings. Furthermore, the survey findings do not necessarily reflect the views or positions of past and present funders. Interested parties can contact IHP for more detailed data and results.